DESIGN OF A CRYOGENIC RANQUE-HILSCH VORTEX TUBE

FOR HYDROGEN COOLING

By

ELIJAH D. SHOEMAKE

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

WASHINGTON STATE UNIVERSITY School of Mechanical and Materials Engineering

MAY 2018

© Copyright by ELIJAH D. SHOEMAKE, 2018 All Rights Reserved

© Copyright by ELIJAH D. SHOEMAKE, 2018 All Rights Reserved

ii

To the Faculty of Washington State University: The members of the Committee appointed to examine the thesis of ELIJAH D.

SHOEMAKE find it satisfactory and recommend that it be accepted.

Jacob Leachman, Ph.D., Chair

Konstantin Matveev, Ph.D.

Dustin McLarty, Ph.D.

iii

ACKNOWLEDGMENT

I’d like to start by thanking the Department of Energy and, in particular, the National

Renewable Energy Laboratory (NREL) for providing so much of the funding to allow this

research to happen. Working with everyone at NREL was wonderful and I appreciate the support

and excitement of the entire team there, and in particular Chris Ainscough who worked tirelessly

to support the project. I’d also like to thank the rest of the team at WSU working on all aspects of

this project: Dr. Konstantin Matveev, Dr. Dustin McLarty, Dr. Jake Leachman, Kevin Cavender,

Marshall Crenshaw, and Carl Bunge.

I’d also like to acknowledge the help of the entire Hydrogen Properties for Energy Research

(HYPER) laboratory. This community has built a wonderful place for learning and growth and is

always supportive. You guys look to improve every day and ensure no one is left alone working

on their project. Particular acknowledgement goes to all of those who spent long hours helping

me to wrangle with the various aspects of design, manufacture, and running of this experiment -

Dr. Patrick Adam, Carl Bunge, Kevin Cavender, Nathan Clarke, Joseph Dufresne, Casey Evans,

Jasper Haney, Nathaniel Jones, Tyler Morton, Austin Rapp, Dr. Ian Richardson, Mitchell Scott,

Katlyn Struxness and Geoff Wendt. I’ve probably forgotten to mention a few you, so many have

contributed. Whether through spirited discussion of design concepts or just hanging around on

late nights and weekends to keep me company as I work, your help has been invaluable. To all of

you, I can’t say thanks enough!

I need to also recognize the hard work of Brandt Pedrow and Ron Bliesner. I have built upon

your designs, and without the years of hard work each of you put into building the experimental

facility my job would have been much harder. I can only hope I have contributed my part to

continue development for the next generation. Speaking of the next generation, thanks to the

iv

massive amounts help from Carl Bunge – you were always there to tackle the next problem with

me and never backed down no matter the challenge. You kept me entertained late nights and on

weekends while we worked, and most importantly of all, you were always the voice of

encouragement pushing me to keep going no matter how many things broke or how frustrating

the problem was. Thanks so much, and I hope the next generation of the experiment goes

smoothly under your leadership!

Finally, a thanks to my family and my friends who supported me throughout the process. Thanks,

in particular to Katlyn Struxness who put up with all the time I was working and couldn’t visit or

call, the times spent talking in the lab instead of someplace fun, and of course the times you

came in to give me a hand. You kept me grounded and wouldn’t let me give up and were always

there to support me when I needed it most. I love you all.

v

DESIGN OF A CRYOGENIC RANQUE-HILSCH VORTEX TUBE

FOR HYDROGEN COOLING

Abstract

by Elijah D. Shoemake, M.S. Washington State University

May 2018

Chair: Jacob Leachman

Small, modular, efficient hydrogen liquefiers are needed to expand use of hydrogen as an energy

currency. The Heisenberg Vortex Tube (HVT) is a novel cooling concept based on the Ranque-

Hilsch Vortex Tube (RHVT) with a catalytic liner – the first concept to reverse the exothermic

ortho-parahydrogen conversion to directly aid primary hydrogen cooling. The development of a

vortex tube suitable for cryogenic hydrogen has never been attempted. Furthermore, the creation

of a vorticial reactor for catalyzing hydrogen spin isomers has not been created. This thesis

shows how such a cryogenic hydrogen vortex tube can be made and integrated with a vorticial

reactor to create the HVT. Analysis of the design parameters of the HVT and experiment are

presented. Initial experimental measurements of this new device are presented of hydrogen at

conditions near 77 K, pressure ratio of 1.9, and cold fraction of 0.38.

vi

TABLE OF CONTENTS

Page

ACKNOWLEDGMENT............................................................................................................ iii

ABSTRACT ............................................................................................................................... v

LIST OF TABLES..................................................................................................................... ix

LIST OF FIGURES .................................................................................................................... x

CHAPTER ONE: INTRODUCTION.......................................................................................... 1

Problem Statement: ................................................................................................................. 1

Proposed Solution: .................................................................................................................. 1

History of hydrogen liquefaction: ........................................................................................... 1

Early Vortex Tube History: ..................................................................................................... 4

Applications and Continued Development: ............................................................................. 6

Current State of the Art and the HVT: ..................................................................................... 7

CHAPTER TWO: THEORY ...................................................................................................... 9

Orthohydrogen and parahydrogen: .......................................................................................... 9

Catalyzing the ortho-para reaction: ....................................................................................... 13

Using the para-ortho conversion for cooling: ........................................................................ 14

The Heisenberg Vortex Tube: ............................................................................................... 15

Addition of the HVT to conventional liquefaction cycles: ..................................................... 17

Vortex tube design theory: .................................................................................................... 18

Flow direction in the Vortex tube: ......................................................................................... 18

Parts of the Vortex Tube ....................................................................................................... 19

vii

Inlet Design .......................................................................................................................... 20

Cold Orifice Design .............................................................................................................. 21

Hot End Design .................................................................................................................... 21

Tube Design ......................................................................................................................... 22

Pressure Ratio ....................................................................................................................... 22

Other Considerations ............................................................................................................ 23

CHAPTER THREE: EXPERIMENTAL DESIGN.................................................................... 24

Cryo-catalysis Hydrogen Experimental Facility: ................................................................... 24

Selecting proper temperature measurement devices: ............................................................. 25

Modifying a commercial vortex tube for cryogenic use: ........................................................ 28

Designing a custom cryogenic vortex tube: ........................................................................... 30

Flow Configuration ............................................................................................................... 32

Inlet Quantity ........................................................................................................................ 33

Inlet Shape ............................................................................................................................ 33

Orifice Ratio ......................................................................................................................... 33

Roughness ............................................................................................................................ 34

Divergence ........................................................................................................................... 34

Detwister .............................................................................................................................. 35

Muffler ................................................................................................................................. 35

Conclusions from the House of Quality................................................................................. 36

HVT Design ......................................................................................................................... 36

Cryogenic Seals: ................................................................................................................... 37

Tubes: ................................................................................................................................... 39

viii

Spin Generator Design: ......................................................................................................... 40

Performing a test of the HVT: ............................................................................................... 42

CHAPTER FOUR: RESULTS AND ANALYSIS .................................................................... 46

HVT Results: ........................................................................................................................ 46

Error Analysis and Uncertainty: ............................................................................................ 47

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS ........................................ 49

Conclusions from this research: ............................................................................................ 49

Recommendations for future research: .................................................................................. 50

APPENDIX .............................................................................................................................. 57

CHEF Safety Plan ..................................................................................................................... 58

Revision Information: ........................................................................................................... 58

Scope .................................................................................................................................... 58

Background Information ....................................................................................................... 58

Operating Procedures ............................................................................................................ 61

Management of Change Procedures ...................................................................................... 78

CHEF Design Documentation ................................................................................................... 81

Revision Information: ........................................................................................................... 81

Electrical .............................................................................................................................. 81

Mechanical / Fluid ................................................................................................................ 89

Software, Data Collection, and Control ................................................................................. 95

ix

LIST OF TABLES

Page

Table 1. Relative weight scoring of cryogenic vortex tube engineering parameters. .................. 32

Table 2. Flow configuration design comparison. ....................................................................... 32

Table 3. Inlet nozzle quantity design comparison. ..................................................................... 33

Table 4. Inlet shape design comparison. .................................................................................... 33

Table 5. Orifice Ratio (d/D) design comparison. ....................................................................... 34

Table 6. Roughness design comparison. .................................................................................... 34

Table 7. Divergence design comparison. ................................................................................... 35

Table 8. Detwister design comparison. ...................................................................................... 35

Table 9. Muffler design comparison. ......................................................................................... 35

Table 10. HVT Tests................................................................................................................. 46

Table 11. Errors associated with experimental equipment. ........................................................ 47

x

LIST OF FIGURES

Page

Figure 1. The gas liquefaction cycle first patented by D.W. Hughes in 1950 (32) ........................ 6

Figure 2. Equilibrium composition of hydrogen isomers ........................................................... 11

Figure 3. The Heisenberg Vortex Tube Concept ....................................................................... 15

Figure 4. Modified Linde-Hampson cycle with HVT ................................................................ 17

Figure 5. An example of a counter-flow vortex tube ................................................................. 19

Figure 6. CHEF Process Flow Diagram .................................................................................... 26

Figure 7. Modified Vortec 106-2-H .......................................................................................... 28

Figure 8. Primary house of quality for a cryogenic vortex tube design. ..................................... 31

Figure 9. HVT complete design ................................................................................................ 37

Figure 10a, 10b. The rifled tubes manufactured to increase tube surface area. ........................... 40

Figure 11. Several generations of spin generator. ...................................................................... 41

Figure 12. An example of typical data from a test of the HVT................................................... 45

xi

Dedication

For friends and family,

who are always there for you

when you need them.

1

CHAPTER ONE: INTRODUCTION

Problem Statement:

Ten hydrogen liquefaction facilities produce the majority of hydrogen in North America

(1). The increased mass per delivery of liquid hydrogen is likely to become increasingly

important as automotive hydrogen refueling stations see increased utilization. The cost to

produce and deliver liquid hydrogen varies based on location and the delivery costs can be 3-4

times the production costs. To address these needs, the Department of Energy has specified the

following targets for hydrogen liquefaction: improving liquefaction cycle efficiencies from a

figure of merit (FOM) of 0.35 to >0.5, lowering liquefier capital costs below $2.5 million/tonne

per day, and achieving these metrics in systems as small as 5 tonne per day (2).

Proposed Solution:

To help realize these goals, I have investigated a Heisenberg Vortex Tube (HVT) as a

device to utilize the endothermic para-orthohydrogen conversion to aid in primary refrigeration

of a hydrogen liquefaction cycle. This application, first proposed by Dr. Jacob Leachman, takes

advantage of differing energy in hydrogen’s allotropes to shuttle energy through a working

system and has the potential to lower cost and maintenance of hydrogen liquefaction.

History of hydrogen liquefaction:

When hydrogen was first recognized as an element in the 18th century, common belief

held that it belonged to a group of substances known as “permanent gasses” – these gasses

seemed impossible to liquify despite the conditions the gasses were placed in (3). Indeed, with

(normal) hydrogen having an incredibly low critical temperature of 33.145 K (4), hydrogen does

2

not exist as a liquid at any pressure with the temperatures achievable at the time. Throughout the

19th century, investigation into refrigeration and consistent improvements in methods of

obtaining low temperature allowed liquefaction of all the “permanent gasses” save hydrogen and

helium (5). While all of these gasses were difficult to liquify due to their low boiling points (and

therefore large amounts of energy involved), hydrogen and helium are unusual in the fact that

their Joule-Thompson coefficient of expansion is negative at standard conditions. What this

means in a physical sense is that free expansion, commonly used for cooling in gas liquefaction,

will actually heat hydrogen or helium at atmospheric temperature and pressure. In fact, hydrogen

will only cool through free expansion to one atmosphere of pressure below 200.5 K (4, 6) and

helium below 45.2 K (6, 7).

In 1898, Sir James Dewar would become the first to succeed in liquefying hydrogen by

precooling gaseous hydrogen with liquid nitrogen under 180 atmospheres, then using free

expansion into an insulated, liquid nitrogen cooled vessel (Kamerlingh Onnes succeeded in

liquifying the final gas, helium in 1908) (5). The key to liquefying hydrogen was to ensure it was

precooled below the Joule-Thompson inversion temperature before expanding it for final

liquefaction, and the key to being able to keep the hydrogen was using a precooled, silvered,

vacuum insulated container. This process was formalized into the first hydrogen liquefaction

cycle by implementing a precooled Linde-Hampson cycle. Two independent implementations of

a cycle whereby gas is compressed to a high pressure, run through a heat exchanger with the

resultant cooled gas, and finally through an expansion valve were patented in 1895 by William

Hampson (8) and Carl von Linde (9). By adding an additional liquefaction cycle to precool the

Linde-Hampson invention, hydrogen can be brought well below the inversion temperature and

liquefied.

3

The next innovation in the liquefaction of gasses was the invention of the Claude liquefaction

cycle by Georges Claude in 1902. The Claude process builds upon the Linde-Hampton process

by adding an expander (isentropic in the ideal case) before the Joule-Thompson device at the end

of the cycle (10). Additional heat exchangers and regenerators may also be added to the cycle to

improve performance. The expander in this cycle pulls work from the expanding fluid, reducing

irreversibility associated with free expansion and therefore increasing efficiency of the system.

Technically, the Joule-Thompson valve at the end of the Claude cycle is not necessary, as

liquefaction could be designed to occur in the expansion device. This is usually not seen, as the

high performance turbo-expansion devices used in modern liquefaction cycles do not handle

two-phase flow well (10). Claude’s is still the basis for most hydrogen liquefaction today, with

optimizations in heat exchanger configuration and expansion devices.

The final key development allowing for modern liquefaction cycles was the discovery of the spin

isomers of hydrogen and their conversion. In 1912, Dr. A Eucken reported a hysteresis when

comparing the heat capacity curve of hydrogen. As the hydrogen cooled to the liquefaction point,

heat capacities differed from those obtained as the hydrogen was warming (11). It wasn’t until

the development of quantum mechanics in the next few years that an explanation could be found.

In 1926 Heisenberg used the developments of quantum mechanics to propose two different

isomers of helium - parahelium and orthohelium and in 1927 extended this proposal to hydrogen

with the help of Hund (12). Two years later, Harteck and Bonhoeffer were able to take the first

experimental measurements to verify the existence of hydrogen spin isomers (13).

The discovery and isolation of parahydrogen was not only able to explain Eucken’s initial

measurements of hydrogen heat capacity, but also explained the unexpectedly quick boiloff of

stored liquid hydrogen. Hydrogen sitting as a liquid will convert from higher energy

4

orthohydrogen to lower energy parahydrogen, creating a significant heat load to the stored

hydrogen. The discovery of effective catalysts allowed for this conversion much earlier, as the

hydrogen is being cooled in the liquefaction cycle, meaning long duration storage of liquid

hydrogen could finally be accomplished. Further discussion of orthohydrogen and catalysts is

given in chapter two.

Early Vortex Tube History:

The vortex tube must have originally been invented by G. J. Ranque in France sometime

in the late 1920’s, as the first recorded reference of the invention is a French patent in December

1931, later extended to the United States and finalized March 1934 (14). As Ranque was a

metallurgist at a French steel works it is speculated that he first observed the effect working with

cyclone separators, however had already significantly advanced the designs by the time the

patent was submitted in 1931 (15). In the patent, Ranque describes his device as

“a method for automatically obtaining, from a compressible fluid (gas or vapor) under pressure, a current of hot fluid and a current of cold fluid, that transformation of the intial fluid into two currents of different temperatures taking place without the help of any moveable mechanical organ, merely through the work of the molecules of fluid upon one another.” (14)

Ranque details in the patent what is still the most common vortex tube geometry today – a

counter flow arrangement where an inlet tangent to the tube generates vertical flow, the

outermost flow being let out one side of the tube, while the innermost flow is returned through

the tube to exit the other side. Ranque also suggests a few modifications that could be made to

the geometry in future tests. These modifications include changing inlet geometry and number,

creating a parallel vortex tube, and using turbine like guides to generate a vortex instead of a

tangential vortex generator. Many of these modifications will later be tested in attempts to

5

improve vortex performance. Shortly following submission of the patent, Ranque gave a talk on

his invention at the Société Française de Physique (16), but is dismissed as having made errors in

his use of total and dynamic temperature by Brun (17). Whether due to this dismissal, or to

disappointing results during his continued research we can’t say, but no further information on

vortex tube design or development comes from Ranque.

Perhaps because of this dismissal, the vortex tube is unseen until Dr. R. Hilsch of the University

of Erlangen in Germany reads Ranque’s paper in 1944. Hilsch hopes to further the development

of the vortex tube to enable it’s use as an inexpensive cooling system for underground mines and

shafts. Ultimately unsuccessful in this goal, Hilsh is able to apply the vortex tube as a substitute

ammonia pre-cooler in his lab’s air liquefaction plant, the first known use of the vortex tube in a

gas liquefaction cycle (15).

Following the end of World War II, C.W. Hansell of the U.S. and British Technical Industrial

Intelligence Committee and R.M. Milton of Johns Hopkins University independently visit the

University of Erlangen and see Hilsch’s work on the vortex tube. R. M. Milton brings back a

working model of the vortex tube as well as a thesis by Hilsch, having the thesis translated (15).

Hilsch’s paper on the vortex tube, or Wirbelrohr as he calls it, was published in the German

Zeitschrift für Naturforschung (Journal of Natural Science) in 1946 (18), and Milton completed

his own studies in the same year, including studies with hydrogen – proving the vortex tube was

not a device simply relying on Joule-Thompson expansion to work (19). Milton’s outreach

included a series of articles in engineering publications claiming the vortex tube to be a

“Maxwell’s Demon” that could produce temperature separation (traditionally in violation of the

second law of thermodynamics, although no such claims were made about the vortex tube) by

some unknown careful selection of low and high energy molecules (19, 20). These publications

6

helped to make the vortex tube a popular subject in technical magazines from late 1946 into

1947, as articles appeared in many trade journals and magazines including Fortune (21), Popular

Science (22, 23), Scientific American (24), and many others (25-31). The vortex tube had finally

gained acceptance, however scientists and engineers quickly found that the inefficiency of even

the best optimized vortex tubes couldn’t compete with more complicated refrigeration cycles

already in use (15). The public’s fascination with the vortex tube as a miracle cooler declined,

but research attempting to understand the physics behind the vortex tube has continued.

Applications and Continued Development:

Presumably inspired by Hilsch’s creation of a vortex tube air liquefaction plant as well as

the vortex tube fervor of the late 1940s, Darrel W. Hughes applied for a vortex tube liquefaction

patent for the Phillips Petroleum Company in 1948 (32). The design, shown in Figure 1 below,

uses the vortex tube directly to cool a gas stream that is then liquefied using the Joule-Thompson

effect in an expansion valve. The remaining gas is also expanded to drop the pressure before

being run through several heat exchangers to precool the incoming gas stream. A compressor

recompresses the recycled gas for continued use.

Figure 1. The gas liquefaction cycle first patented by D.W. Hughes in 1950 (32)

7

As I have been unable to find a mention of such a vortex tube gas liquefaction cycle used at

scale, it seems unlikely to have proven economically feasible to operate. While the vortex tube

seems miraculous, many researchers have continued to find it inefficient in comparison to

conventional cooling cycles (33).

The inherent simplicity and robustness of the vortex tube has led to focus in some applications

where reliability, mass, and/or space are highly valued. An early example of this is a NASA

report by J. M. Nash in 1970 examining the vortex tube for application in environmental control

systems on board spacecraft (34).

Current State of the Art and the HVT:

Currently, vortex tubes are mainly used for industrial cooling applications where

compressed air is already available. Examples of these kinds of applications include cooling and

chip removal in industrial machining, cooling of electronics enclosures, and industrial spot

cooling applications. Several companies have developed commercial vortex tube models to meet

the needs of these markets, including Exair (35), ITW Vortec (36), and AiRTX (37). These

vortex tubes range from 2-150 SCFM of 100 psi compressed air, typically with adjustable cold

fractions of 20% - 50% of the flow (35-37). While fine for cooling of small systems, this is far

from the scale needed for industrial liquefaction of gasses. No operating commercial liquefier is

currently known to utilize the vortex tube. In fact, little research has been done on any vortex

tube configuration which could be used in a cryogenic gas liquefaction environment.

Furthermore, few studies have looked at performance of vortex tubes with gases other than air or

nitrogen.

8

The subject of this thesis, the Heisenberg Vortex Tube, was submitted for a patent by J. W.

Leachman in 2016 (38). The novel HVT concept combines the advances of previous vortex tube

design with a catalyst coating that can convert between allotropic forms of hydrogen, creating an

energy shuttle that can increase cooling in the vortex tube. This invention promises to be capable

of improving hydrogen vortex tube performance in areas where the vortex tube is already

beneficial and may provide enough benefit to finally allow a vortex tube liquefaction cycle

competitive with current cycle designs.

The first step to realizing this potential is the creation of a working HVT design, to show the

concept is viable and to get data to aid in design, analysis, and optimization of the new invention.

The HVT is designed for primary cooling following a liquid nitrogen or liquid air precooling

stage, and therefore the HVT design must be cryogenic compatible and tested to operate near

liquid nitrogen temperatures of 77 Kelvin. This is a challenging goal, as vortex tube designs that

will operate in a cryogenic environment are not available. Vortex tube performance optimization

and compatibility with hydrogen has also not been a focus of any previous research. Finally,

hydrogen spin isomer catalyst studies have never been attempted in vorticial tube flow. Thus, the

goal of this thesis is to provide these building blocks upon which further research can be built -

to create a hydrogen vortex tube capable of testing the catalyst coatings on the will of a HVT at

77 Kelvin and below.

9

CHAPTER TWO: THEORY

Orthohydrogen and parahydrogen:

Spin isomers arise due to the nature of quantum mechanics – where all particles are

described as both discrete particle and wave. The wave properties can be described with the

Schrödinger wave equation, defined in equation 1.

!"# + 8&"'ℎ" (* − ,)# = 0 1

In this representation, the wave equation Ψ is defined with respect to mass m, total energy *,

potential energy ϕ, and Planck’s constant h. When discussing a molecule, such as H2, the wave

equation can be broken up based on independent energy modes of the molecule, such that the

total wave function Ψtot, is given in terms of translational energy modes Ψtrans, rotational energy

modes Ψrot, vibrational energy modes Ψvib, electronic ground state Ψelec, and nuclear spin Ψspin, as

shown in equation 2. It should be noted that at higher temperatures, and therefore higher energy

levels, the assumption that these energy modes are independent may no longer be safe. As our

interest is in cryogenic hydrogen, low energy assumptions of independent modes are safe (39).

#232 = #24567#432#89:#;<;=#7>96 2

The assumptions of quantum mechanics have been shown to lead to two possible solutions to

linear combinations of wave equation for multiple particles – a symmetric and an antisymmetric

combination. Only one of these solutions can be valid without violating an important tenant of

quantum mechanics, namely that two identical particles in a system cannot be distinguished. It

has been shown experimentally that the Ψtot for particles with half-integral spin will be anti-

symmetric, and particles with integral spin will have a symmetric Ψtot (39). When combining

terms, as in equation 2, two like terms will result in a symmetric wave equation, whereas an

10

antisymmetric and symmetric wave equation will create an antisymmetric combined wave

equation.

Considering a hydrogen molecule consisting of two protium atoms (a single proton with single

electron), we can make the following assumptions about symmetry: 1. Ψtrans is dependent upon

only the center of mass of the molecule, 2. vibrational state can be assumed to be that of

harmonic oscillator, making Ψvib only dependent upon the distance of separation of the nuclei.

Neither of these recognize differences in the hydrogen atoms, and therefore do not impact

symmetry. Ψelec has been shown to be symmetric with respect to nuclear change, meaning the

resultant symmetry of Ψtot will match that of the combination symmetry of the remaining terms,

Ψrot and Ψspin. Because the protium nucleus is made of a single neutron, we know nuclear spin

quantum number mn = ½, and therefore Ψtot must be antisymmetric (39).

We can now use this information to assemble a partition function for hydrogen. Because Ψtot

must be antisymmetric, ΨrotΨspin must also be antisymmetric. For even rotational energy levels j,

Ψrot will be symmetric and Ψspin must be antisymmetric. For odd j, the opposite is true. From

these conclusions, equations 3 and 4 can be developed for a molecule with half-integer nuclear

spin (39).

@46(3AA) = B6(B6 − 1)

2 ∗ D E(2F + 1) ∗ GHIJK L(LMN)O

L

P,",R,….+

B6(B6 + 1)2 ∗ D E(2F + 1) ∗ GH

IJK L(LMN)O

L

N,U,V,…. 3

B6 = 2 ∗ X6 + 1 4

We now see that the total energy content for this substance is a sum of two components – those

molecules with even rotational energy level and those with odd rotational energy level. The first

11

has been defined parahydrogen and the second orthohydrogen. By applying our knowledge that

mn of hydrogen is ½, and comparing the parahydrogen half of the partition function to the

orthohydrogen half, we can define equation 5 to give the ratio of orthohydrogen to parahydrogen

at any temperature T. In this equation, θr is the characteristic rotational temperature of hydrogen,

85.4K (an accepted value for low temperature applications of hydrogen) (39).

Z342[3Z>545

= 3 ∗ ∑ E(2F + 1) ∗ GH

IJK L(LMN)OL

N,U,V,….

1 ∗ ∑ E(2F + 1) ∗ GHIJK L(LMN)OL

P,",R,….

5

Using this equation, a plot of the equilibrium composition versus temperature is provided in

Figure 2. The plot shows that at low temperatures, a majority of hydrogen molecules fall to the

even rotational ground state of j=0, and the equilibrium composition is almost pure

parahydrogen. As temperature rises, hydrogen molecules begin to exist in higher energy levels

and the composition asymptotically approaches a 3:1 ratio.

Figure 2. Equilibrium composition of hydrogen isomers

0 100 200 3000

0.25

0.5

0.75

1

Temperature [K]

Ort

hohy

drog

en F

ract

ion

12

Because the corresponding rotational energy level for orthohydrogen is always one higher than

that of parahydrogen (ground state parahydrogen corresponds to j=0, whereas the lowest energy

state of orthohydrogen is j=1), parahydrogen has a measurably lower rotational energy than

orthohydrogen. It can therefore be assumed that energy will be released when orthohydrogen

converts to parahydrogen, and energy will be absorbed in the reverse conversion. Indeed, when

orthohydrogen converts to the para form at the normal boiling point, a “latent heat of

conversion” of 703 kJ/kg is released (40). If left as normal hydrogen, this would mean a release

of 527 kJ/kg, greater than the latent heat of vaporization at the normal boiling point (448 kJ/kg)

(4, 6).

It can now be seen how this presents a major problem when attempting hydrogen liquefaction.

As was shown on Figure 2, high temperature hydrogen is roughly 75% orthohydrogen. As the

hydrogen cools, the equilibrium fraction of parahydrogen increases steadily, and is nearly 100%

parahydrogen by the time the normal liquefaction point is reached. Further complicating matters,

a lone hydrogen molecule cannot convert between orthohydrogen and parahydrogen on its own.

Interaction with another catalyst molecule is required to promote a nuclear spin flip in the

hydrogen molecule and allow for conversion between parahydrogen and orthohydrogen (12).

While hydrogen can self-catalyze this reaction, the timescale for this to occur in a gas is much

longer than will be seen by any useful liquefaction process – an early estimate by Hall and

Oppenheimer gives a reaction half-life of 108 seconds, or approximately 3 years (41). Milenko

and Sibileva confirmed this value with measurements in 1996 that predicted a maximum

conversion rate of normal hydrogen to 99.8% parahydrogen in 3.06 years (42).

If the gas interacts with a catalytic material however, conversion between the two states occurs

much faster. The first catalyst materials were discovered in trying to examine the conversion

13

process – hydrogen kept in brass and iron containers were noted to have higher reaction rate than

that given above by Hall and Oppenheimer, and these rates changed in proportion to the surface

area of the container (12). The discovery that the ortho-parahydrogen conversion can be

catalyzed led to a solution to the liquid hydrogen storage problem – if converted in the process of

liquefaction, the latent heat of conversion can be removed as the hydrogen is cooled and the

resulting liquefied hydrogen will be almost completely parahydrogen at the end of the

liquefaction cycle.

Catalyzing the ortho-para reaction:

The necessity of catalyst in an industrial liquid hydrogen cycle led researchers to attempt to

understand the conversion process and create the most cost-effective catalysts possible. To

determine the best catalyst, non-equilibrium hydrogen is typically run through a packed bed

reactor of the catalyst at a defined temperature and the mass of hydrogen converted is compared

to the mass of catalyst required to make the conversion.

One measure of this activity has been defined as β’ in literature, given by equation 6 below (43).

^_ = `abbcdeafaghbf ∗ `ai%k"eclmGnfopgGafqG'rGnafsnG ∗ 70%`abbcdk"eclmGnfGurGnvGwclu ∗ %k"eclmGnfGu

6

This value gives an idea of the mass efficiency of the catalyst, defined by the mass of catalyst

required to convert and mass of hydrogen and the percent of hydrogen flow converted compared

to 70% of the hydrogen possible to convert. Because this 70% is an arbitrary scaling factor,

Pedrow updated this value to β*, given in equation 7 below (44). In both equations, a smaller β’

or β* means a more effective catalyst.

^∗ = `abbcdeafaghbf ∗ `ai%k"eclmGnfopgGafqG'rGnafsnG`abbcdk"eclmGnfGurGnvGwclu ∗ %k"eclmGnfGu

7

14

A common formulation for ortho-para catalysis is Fe2O3, sold under the brand name Ionex™.

The performance of this catalyst has now been surpassed in more recent studies. One of the more

thorough such studies is an examination of several catalysts by Brooks, Wang and Eyman

performed for NASA in 1994 (43). This study looked at many transition metal silicates, as well

as Ruthenium based catalysts supported on silicon substrates. These materials were then

compared to a Nickel Silicate catalyst produced by Air Products with a typical β’ value of 20 sec.

that was commonly used in industry. Nickel Silicates proved to be far better than the other

transition metal silicates, with β’ values as low as 11 sec. depending on sample preparation. The

ruthenium catalyst significantly outperformed the silicates, with minimum β’ as low as 1.81 sec.

in some preparations. Air Products applied for a patent on creating such highly active ruthenium

silicate catalysts as well as ruthenium aluminate catalysts in 1989, the patent was granted in 2017

(45). Pedrow conducted testing using a Fe2O3 catalyst similar to Ionex™, as well as RuO2 based

catalysts and confirmed the prior literature predicting the RuO2 catalysts to produce better results

(β*RuO2 = 988.4 sec vs. β*Fe2O3 = 1615 sec). Interestingly, a support material coated in Fe2O3 and

then re-coated in RuO2 performed even better than the samples coated solely in RuO2 (β* = 915

sec), although no explanation for this was given (44).

Using the para-ortho conversion for cooling:

While the necessity of ortho-para conversion in a liquefaction process has been applied

from the early days of liquid hydrogen production, a newer application is using the reverse

reaction for cooling. While hydrogen gas is warming, the equilibrium hydrogen concentration

shifts to be more orthohydrogen heavy. If a catalyst allows this conversion to happen, the energy

of conversion is stored in the rotational spin state of the newly converted orthohydrogen. This

15

energy must come from somewhere and, absent other sources, will come from the kinetic energy

of the hydrogen gas itself, resulting in temperature drop. Ronald Bliesner demonstrated this in

his 2013 work, showing a cooling power increase of 35% using hydrogen vapor catalyzed by a

packed-bed reactor of Ionex™ when compared to the same reactor packed with non-catalytic

aluminum (46). Brandt Pedrow extended this work with an analysis of catalyst coating on multi-

layer insulation scrim material, showing a 12% increase in cooling power over uncoated scrim

and demonstrating that catalysts can increase cooling in non-packed bed configurations (44).

The Heisenberg Vortex Tube:

The HVT principle works to combine these previous discoveries to create a device that

utilizes para-orthohydrogen catalysis as an energy shuttle to transfer energy from cooler parts of

a liquefaction cycle to warmer parts of the liquefaction cycle where cooling is more efficient, as

shown in Figure 3.

Figure 3. The Heisenberg Vortex Tube Concept

Hydrogen is input to the vortex tube after some precooling has occurred, fully catalyzed into the

inlet A. As the hydrogen flows into the tube, a vortex is generated and temperature separation

begins, with warmer hydrogen on the periphery and cool hydrogen in the center, as shown

through B. The equilibrium concentration of this warmer hydrogen is now shifted higher in

F

A B

C

D E

16

orthohydrogen concentration. Catalyst coating along the wall of the tube at C will allow an

endothermic conversion of hydrogen isomers from the previous equilibrium concentration to the

new, orthohydrogen rich concentration. If the tube is placed in a vacuum, or well insulated at D,

the endothermic reaction cannot pull energy from the environment and must instead pull energy

from the hydrogen itself, causing bulk cooling. At E, the heated hydrogen will leave the HVT

with higher orthohydrogen concentration, while at F, cooled hydrogen will leave the HVT to

continue the liquefaction process. The heated hydrogen can optionally be recycled back to be re-

cooled and converted to release the energy stored as orthohydrogen.

As an example, case, let’s consider this to be a precooled hydrogen stream at 77 K and fully

catalyzed to the equilibrium concentration of 50% orthohydrogen, 50% parahydrogen entering

the tube at A. If the vortex tube is designed such that it can deliver 10 K increase in temperature

on the hot stream and 5 K decrease in temperature on the cold stream, the hydrogen on the

outside of the tube is now 87 K, and the equilibrium concentration approximately 57%

orthohydrogen. A highly effective catalyst allows for conversion of 71% of this potential,

making the outlet concentration of this hydrogen gas 55% orthohydrogen, 45% parahydrogen.

Using this scenario, we can calculate the additional energy sequestered in the hydrogen. In this

case, we have converted an extra 5% of the flow from parahydrogen to orthohydrogen at a

temperature of 87 K. At this temperature, the enthalpy of conversion from parahydrogen to

orthohydrogen is 668.6 kJ/kg (40), meaning the sequestration of 33.43 kJ/kg of hydrogen

converted. If we assume a reasonable vortex tube cold fraction of 30%, this gives us a storage of

23.40 kJ/kg of total hydrogen flow. While the numbers in this example are approximate, the

thought process and calculation are valid for a real-world vortex tube with given performance

and catalyst of given activity.

17

Addition of the HVT to conventional liquefaction cycles:

By using the HVT, energy can be shuttled between a cold state where cooling is

inefficient and difficult to a warmer state where cooling is relatively less expensive. An

imagining of such a modification to the conventional Linde-Hampson cycle is illustrated in

Figure 4. In this example, a HVT has been added after the initial precooling from a co-located

nitrogen liquefaction cycle, but before the final free expansion through a Joule-Thomson valve

for liquefaction.

Figure 4. Modified Linde-Hampson cycle with HVT

Such a modification to a classical liquefaction cycle could also be used with the Claude cycle in

a similar manner if an expansion device is added before and/or after the HVT. Marshall

18

Crenshaw examined many of these cycles in 2017 and reported the theoretical predicted

performance of these modifications and their potential to reduce the cost of hydrogen

liquefaction (47).

Vortex tube design theory:

Several reviews of vortex tube operating principles, theoretical treatments and

experimental results are available. Despite this considerable body of research, an accepted

standard for predicting vortex tube performance is not available and data on optimal design

considerations varies significantly. Fortunately, some guidelines for design can be drawn from

findings where a majority of the experimental results agree. Of particular help were a few vortex

tube review papers that collected the results of decades of work to reach conclusions. Some of

these include the works of Eiamsa-ard and Promvonge (48), Gao (49), and Yilmaz (50). Each of

these studies or reviews attempted to understand the working behavior of vortex tubes and how

vortex tube geometry impacted performance. None of these reviews examined either cryogenic

designs of a vortex tube, performance in the cryogenic regime, or hydrogen as a working fluid. I

have done my best to succinctly summarize this large body of work in the following sections,

however a deeper dive into the literature (particularly the review papers) is recommended for

anyone looking to advance the state of vortex tube research.

Flow direction in the Vortex tube:

Two vortex tube designs are presented in literature, parallel or uniflow and counter flow.

A uniflow vortex tube only has a single inlet and single exit, with two coaxial tubes being

attached at the exit. The inner tube captures the cooler inner flow, while the outer tube captures

the hotter outer flow. The vortex tube designs previously discussed in this work are counter flow

19

tubes, with separate hot and cold exits for the gas flow. Most vortex tubes are counter flow, as

repeated studies have shown higher performance in these devices (48, 49, 51).

Parts of the Vortex Tube

Figure 5. An example of a counter-flow vortex tube

Part of the complexity of optimizing a vortex tube arises from the number of geometric

features in the device that can have large impact on gas flow, and therefore performance. Figure

5 above is an example of a counter-flow vortex tube, similar to what you might buy online for

spot cooling. In this design, gas first enters a plenum (A) which, due to the relatively large

volume, simply acts as a static pressure region to drive flow through all inlets evenly. Single inlet

vortex tube designs may not have a plenum, but rather attach the gas inlet directly to the inlet of

the vortex tube. In this design, the inlets (B) are built into a section known as the spin generator,

which also houses the cold orifice (C). The inlets are designed such that they generate vorticial

flow as close to the front of the cold orifice as possible. The cold orifice does not allow flow

back into the cold end of the tube, forcing it to expand outward toward the hot end of the tube as

it spins. While in the tube (D), the gas separates into the original outer flow region that heats and

a backwards spinning inner flow region formed in the central low-pressure region of the tube. An

angled stopper at the end of the tube (E) is typically used to only allow the hot outer flow gasses

H A

B

C

D E F G

20

to leave the tube, while preventing any of the cool inner flow from leaving. This stopper is also

usually adjustable so that it is possible to change the amount of flow moving out the cold end vs

the hot end of the tube. Some sort of flow rectifier or flow straightener (F) is usually found just

before or just after this stopper to remove rotation from the flow. The hot gas then leaves through

the hot outlet of the device (G). The cold flow travels down the center of the tube (D), through

the cold orifice (C), and out the cold end of the tube (H).

Inlet Design

Inlet design can have an important impact on the vortex generated in the vortex tube. The

general goal of proper inlet design is to reduce losses in the flow system to generate a strong

vorticial flow with the smallest pressure drop. Gao (49) recommends that pressure loss over the

inlet should be small, the Mach number at the exhaust of the inlet should be 1, and the

momentum flow at the exhaust should be large. One of the ways to achieve this is to spread a

number of inlets around the tube. An increase in the number of inlet nozzles generally leads to

greater temperature separation (48). One of the ways to minimize pressure losses in the vortex

tube is to adjust the geometry of the inlet as well. Merkulov suggests that a nozzle with

rectangular cross section and helical inlet passage provides a smooth stream entrance and is easy

to manufacture (52). Gao suggests that slot type inlets perform better than cylindrical/conical

nozzles (49).

Another important consideration is the ratio of inlet area to tube are, as a way of characterizing

the restriction placed on a particular size of vortex tube. Early experimentalists characterized this

with respect to inlet diameter to tube diameter ratio and recommended a value of about 0.33 (48),

but when non-circular inlets are considered the area ratio is easier to define. This recommended

21

diameter ratio then becomes an area ratio of about 0.109. Westley recommends a ratio of 0.2

(15), Linderstorm-Lang a ratio of 0.0625 (53), Aydin and Baki a ratio of 0.11 (54), and

Merkulov recommends a range between 0.085 and 0.1 (52), with the majority of designs being

optimal at 0.092.

Cold Orifice Design

Small cold orifice ratios yield higher back pressure, while large cold orifices allow high

tangential velocities into the cold tube, both of which can lower temperature separation.

Optimum values from Eaimsa-ard and Nimbalkar have been estimated at d/D = 0.5. (48, 55),

while Gao claims 0.4 (49) to be the optimal value. This orifice should be as close to the inlet

nozzle as possible to ensure good temperature separation (48) and prevent backflow into the cold

end of the tube before temperature separation occurs.

Hot End Design

Several design considerations can impact the optimal design of the hot exit of the vortex

tube. Traditional designs have a control valve, detwister or flow straightener, and sometimes an

acoustic muffler integrated in the design. Eaimsa-ard estimates the optimal control valve angle of

50 degrees and states that a detwister at the exit has been shown to improve performance (49).

Metenin has no control valve on his vortex tube design, but instead controls back pressure on a

reservoir at the hot and cold exits of the tube to determine the fraction of the air flowing out each

side of the vortex tube (56). Metenin also studied several flow rectifiers: a short grid across the

exit of the tube, a longer cross shape in the middle of the tube, a short latticework of circular

profile across the tube, a longer circular latticework cut in a concave parabola on the trailing

side, and a longer circular latticework cut in a convex parabola on the leading side. He found the

22

grid type rectifier was the best design to promote high performance in the shortest vortex tube

possible. Eaimsa-ard showed that adding an acoustic muffler increases the performance (49) of a

vortex tube.

Tube Design

The primary consideration for designing the tube section of a vortex tube is the aspect

ratio of the tube. This is usually measured in L/D ratio – the length of the tube in tube diameters.

Many recommend a length to diameter of ratio of at least 20 (15, 48, 57), but some sources have

suggested as high as 65 (49). Most of these papers agree that temperature separation increases

with length, but this increase is less significant the longer the tube gets. Metenin states that this

length depends on both the driving pressure ratio and the effectiveness of the flow rectifier,

citing values varying from 2.5 to 24 depending on conditions (56). Another factor in tube design

is the surface roughness on the interior surface of the tube that can generate frictional losses in

the flow. Surface roughness has been found to decrease performance by up to 20% (49). Eaimsa-

ard also found a small divergence can increase performance at shorter lengths. Optimal geometry

suggests an angle of 2-3 degrees (49), which amounted to increases of 20-25% in performance.

Pressure Ratio

The pressure ratio across the vortex tube is typically measured between the inlet pressure

and the pressure of the outlet flow on the hot side of the vortex tube. Optimal efficiency with air

is found to be at around 2 bar inlet pressure, with higher pressures resulting in higher separation

but lower efficiencies (48, 57).

23

Other Considerations

It has been shown that you can operate a double-circuit vortex tube where gas is injected

in the center of the hot end of the vortex tube and continues through to exit the cold side of the

vortex tube. This has been shown to improve performance (49, 58). Multistage vortex tube

systems have also been shown to improve upon a single stage system (49).

While these general considerations are important to the design of the HVT, some caution must be

taken, as almost all of this experimentation has focused on air at room temperatures. It is unclear

how much of these results will be consistent with hydrogen gas or at cryogenic temperatures. Liu

et. al. (59) did examine helium and neon gasses at cryogenic temperatures and were able to

confirm some of the above assumptions stood for cryogenic operations. Once again, four inlet

nozzles showed greater performance than two inlet nozzles, and increased inlet pressures

resulted in higher temperature separation. Neon proved a better cryogenic refrigerant in this

cycle than did helium, with the best test showing a cold temperature 11.4 K below the inlet

temperature and 6.7 K below the hot exit temperature (2.40 MPa inlet pressure).

24

CHAPTER THREE: EXPERIMENTAL DESIGN

The system design utilized an existing test cryostat originally designed to perform ortho-

parahydrogen catalysis experiments and applied lessons learned from both those previous

experiments and the previous vortex tube experiment. The reuse of the cryostat reduced the cost,

both monetary and time, to conduct the experiment, as work had already been done to create a

system that could produce up to 4.5 liters of liquid parahydrogen.

Cryo-catalysis Hydrogen Experimental Facility:

The Cryo-catalysis Hydrogen Experimental Facility (CHEF) was originally developed in 2012 to

investigate the performance of cryogenic catalysts for Parahydrogen-orthohydrogen conversion.

The experiment liquefies hydrogen and converts to the parahydrogen form before flowing

through a catalyst bed and over a calibrated hot-wire para-ortho composition cell (60). In the fall

of 2014 the experiment was refurbished with primarily welded stainless steel plumbing within

the cryostat and two additional catalyst beds were added with a change to a vertical orientation.

This change allowed characterization of deposited Ruthenium-Iron-Oxides for para-

orthohydrogen conversion (44).

The current configuration of CHEF removes one of the catalyst beds, which is replaced with the

vortex tube. The remaining two catalyst beds are used to pre-set the hydrogen inlet condition for

the vortex tube. The temperature-controlled heaters in each catalyst bed can precisely adjust the

inlet temperature for the vortex tube and the presence or absence of a catalyst in the bed allows

the para-orthohydrogen composition to be set (equilibrium condition in the presence of a packed

bed catalyst, condition of the inflowing hydrogen without catalyst). In all current tests, these

catalyst beds are empty, allowing the parahydrogen from the liquid tank to remain parahydrogen

25

until reaching the vortex tube. The vortex tube following the catalyst beds is instrumented with

thermistors at the inlet and each exit of the vortex tube. Each exit flow from the vortex tube is

then instrumented with sensors required for hot-wire composition measurement and mass flow

measurement before being vented outside the building through the laboratory vent stack. The full

process flow for CHEF is shown on the next page in Figure 6.

Selecting proper temperature measurement devices:

There are a number of cryogenic temperature sensing options available including diodes,

resistance thermometry devices (RTDs), thermocouples, and capacitive sensors. The sensors

chosen for this experiment consist of Platinum RTDs, with a single Cernox® sensor. These

sensors were selected according to their intended operating conditions.

RTDs are temperature sensors that operate by measuring voltage across a material with known

resistance changes due to temperature. Platinum is one material that has been standardized as a

RTD material, with industry standard curves and tolerances (61). Platinum RTDs are positive

temperature coefficient RTDs, and therefore have resistance that increases with temperature. My

selection of platinum RTDs for main instrumentation is primarily due to the standardized nature

of the sensor. Firstly, platinum RTDs are inexpensive compared to other options for cryogenic

temperature measurement as they can be easily fit to standard curves without factory calibration.

Additional functionality integrated in the Lakeshore 336 temperature controller allows for a

SoftCal™ to be performed – a transformation of the industry standard curve to fit specific

calibration points for specific sensors. This pseudo-calibration increases accuracy of a platinum

RTD to ±0.25 K across the entire range from 73 K to 305 K using a single point near liquid

nitrogen temperature (~77 K) and a room-temperature point (~295 K). With the ease of creating

Figu

re 6

. CH

EF P

roce

ss F

low

Dia

gram

26

27

accurate enough, inexpensive pseudo-calibrations in the laboratory, managing the large number

of temperature sensors required for the experiment is much simpler and less expensive. In the

event of a broken wire or broken sensor, a new RTD can be purchased cost-effectively and re-

calibrated in the lab. The ease of Soft-Cal™ software also allows for periodic re-calibration of

temperature sensors whenever they have been moved, given new electrical leads, or re-potted in

a new fitting (due to cracked epoxy bonds, etc.). The downside to a Platinum RTD is that they

lose sensitivity below 70 K, and very rapidly lose sensitivity below 30 K (62). This loss of

sensitivity makes platinum RTDs non-optimal for temperatures below 70 K, and unsuitable for

temperatures below 30 K.

Cernox® sensors are a brand of negative temperature coefficient RTDs produced by LakeShore

Cryotronics. Like Platinum RTDs, Cernox® sensors use resistance to measure temperature but

unlike the Platinum sensors, resistance and temperature have an inverse relationship in a

Cernox® sensor. Cernox® sensors also do not conform to a standardized curve, meaning an

expensive calibration from the factory is required for each sensor used. Replacing a Cernox®

sensor is therefore more costly and more time consuming than a standardized sensor. The benefit

to a Cernox® sensor is its wide operating range (0.10 K to 420 K) and high accuracy (Typical

uncertainty less than ±0.040 K from 1.4 to 300 K) compared to the standardized Platinum sensor

(62, 63). The 30-70 K limit on platinum RTD sensors prevented its use on the condenser tank in

CHEF, so a Cernox® that the laboratory already had factory calibrated was used instead to keep

track of condenser temperature.

In order to obtain the most accurate signal from a resistive device, it is necessary to separate the

resistance of the wires used as electrical leads to the device. This is done using a four-wire

28

measurement system on the Lakeshore Model 336. Each lead wire on the RTD is soldered to two

electrical leads, for a total of four wires per sensor. One wire on each lead will be used in

connection with a constant current source in the Lakeshore Model 336 to provide sensor power.

The remaining wire on each lead is used to measure voltage across the sensor, but not across the

electrical leads. From the voltage and current measurements, an accurate resistance value can be

calculated (64).

Modifying a commercial vortex tube for cryogenic use:

The commercial model vortex tube selected for initial testing is a Vortec 106-2-H vortex tube

designed to provide 100 BTU/hr cooling with 2 scfm of air at 100 psig (65). Several

modifications to this tube were made to make it suitable for cryogenic use, shown in Figure 7

below.

Figure 7. Modified Vortec 106-2-H

The Vortec design is easy to disassemble, which made the modification of the vortex tube easy,

however, the design was not made with cryogenic design or hydrogen in mind. The vortex tube

is entirely brass, stainless steel, and a small amount of plastic, meaning all materials were

hydrogen safe. The seals for the inlet and cold exit of the vortex tube were NPT, which is not

29

general lab practice to use with cryogenic hydrogen systems, but can be successfully

implemented (see Bliesner, (60)). The greater difficulty arose from the hot end, which was not

designed to attach to any external piping, the tube sealed with straight threads, and the spin

generator sealed by an elastomeric O-ring.

The hot and cold ends was brazed to a Swagelok VCR® fitting in order to use a reliable metal-

metal seal to connect to the rest of the piping in CHEF. The inlet connection remained NPT

sealed with PTFE tape to prevent braze from interfering with the gas flow into the plenum and

spin generator. The spin generator O-ring was replaced with a thick ring of indium metal that

would crush to provide a seal when the cold end of the vortex tube was attached. The most

difficult issue to solve was finding a way to attach the tube to the hot end fitting and the plenum.

As this had been attached with just a straight thread, the thread would not seal by itself. The tube

also couldn’t be braised because it needed to be switched between the normal tube from Vortec

and a second tube with catalyst plating. In the end the decision was made to also seal this by

tightly wrapping PTFE tape around the straight thread. A final modification to the vortex tube

was the brazing of a small pressure tap onto the plenum of the vortex tube to measure static

pressure of the plenum and compare to the static pressure of the hydrogen tank used to run the

test. The goal of this measurement was to determine if the piping and instrumentation between

the hydrogen tank and vortex tube would cause significant pressure drop that impacted pressure

ratio.

However, even with modifications, the tube proved difficult to seal in a cryogenic environment.

The indium seal had the issue of being crushed by a screw thread, causing a couple issues. First,

despite the fact that the spin generator was free to spin when crushing the indium on the

backside, there was potential to create a shearing force in the indium. This had the potential to

30

create tears in the indium as it was compressing and allow hydrogen through. Secondly, because

indium does not have the elasticity of the O-ring it replaced, any torque applied to unscrew the

cold end fitting would loosen the seal. Because the fitting had already been bottomed out

extruding the indium, the entire seal would need to be replaced anytime this happened. Installing

the cold end of the vortex tube became very difficult as one had to tighten the VCR® fitting to

the correct torque while simultaneously not allowing the cold fitting on the vortex tube side to

unscrew from the plenum.

Somewhat surprisingly, the PTFE seal of the straight thread worked reasonably well once sealed.

Proper application of the PTFE was critical, to ensure no gaps or air pockets were left to allow

hydrogen through the tape barrier, but once a successful seal was made, it remained sealed until

disassembly. This seal was aided by the fact that the inner thread of the seal was on the stainless-

steel tube, while the outer thread was on the brass plenum and end fitting. Brass has a higher

coefficient of thermal expansion than stainless steel (66), and therefore would shrink around the

tube to aid the seal.

Designing a custom cryogenic vortex tube:

Identifying a need for a vortex tube that was both designed to be used in a cryogenic

environment and designed to have reconfigurable geometry, a completely novel vortex tube was

designed. Following a review of past literature (detailed in Chapter 1), a technique from Quality

function deployment (QFD) called the House of Quality was used to provided quantitative

ranking of the engineering design characteristics required of a cryogenic vortex tube. In the first

round of this House of Quality, requirements of the experiment were ranked with the impacts

31

they had on the engineering design characteristics of completed vortex tube, as shown in Figure

8.

Figure 8. Primary house of quality for a cryogenic vortex tube design.

Each requirement of the cryogenic vortex tube design was given a weighting out of 10, as judged

by a meeting of experimental stakeholders (myself, my advisor, and Chris Ainscough at NREL):

32

low installation cost – 7, high reliability – 6, low operating cost – 10, quick ramping – 3. These

ratings were then converted to relative weights and multiplied by the score of each engineering

design characteristic to provide a total value that engineering characteristic had for the design.

These total scores converted to a relative weighting value as a percentage of importance. The

results are summarized below.

Engineering design characteristic Relative weight Machinability 10.26% Maintenance 14.66% Cryogenic Compatibility 14.82% Conversion Rate 16.12% Cost 10.26% Hydrogen Compatibility 14.82% Thermal Mass 4.40% Temperature Separation 14.66%

Table 1. Relative weight scoring of cryogenic vortex tube engineering parameters.

These engineering design parameters, now summarized in terms of importance to the project

were used to narrow design options for a number of geometric design considerations for the

vortex tube. Scoring for each possible design are given in the following sections, with irrelevant

engineering characteristics removed.

Flow Configuration

Uniflow Counter Machinability 10.26 9 7 Temperature Separation 14.66 7 9 195.0 203.8

Table 2. Flow configuration design comparison.

The flow configuration decision was pretty straightforward, as literature agreed closely

that a counter flow design would be better than the uniflow configuration (See chapter two). The

uniflow design would have some mild benefits in terms of ease of manufacture. The final

breakdown in scoring is given above in Table 2.

33

Inlet Quantity

1 2 3 4 5 6 7 8 9 Machinability 10.26 9 9 9 8 8 7 6 5 4 Cost 10.26 9 9 9 8 8 8 7 7 7 Temperature Separation 14.66 2 4 5 6 7 8 8 9 9 214.0 243.3 258.0 252.1 266.8 271.2 250.7 255.0 244.7

Table 3. Inlet nozzle quantity design comparison.

Literature showed that generally more inlets produced a more even vortex with fewer

losses, however increased inlet quantity created problems by requiring more smaller inlets for the

same amount of flow. This reduced machinability and increased cost in terms of tooling required

to manufacture the spin generator. Based on Table 3, three to six inlets were decided on with

multiple spin generators to be made in each condition. This would enable experimentation to find

the optimum for our operating conditition.

Inlet Shape

Tapered, Slotted Slotted Conical Cylindrical Machinability 10.26 2 5 4 9 Temperature Separation 14.66 9 5 7 4 Total Score 152.44 124.59 143.65 150.98

Table 4. Inlet shape design comparison.

As discussed in chapter two, inlet shape can have impact on pressure losses in the

transition from the plenum to the vorticial flow in the vortex tube. A tapered, slotted spin

generator has been shown to have the best performance but can be difficult to machine. A pure

cylindrical inlet can be easily drilled tangent to the inside tube wall but is more likely to create

losses at its inlet and exit. Table 4 above shows that the performance increase for the tapered,

slotted inlet makes up for its difficulty in manufacture.

Orifice Ratio

34

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 8 Machinability 10.26 8 9 9 9 9 9 9 8 7 Thermal Mass 4.40 1 1 2 2 2 2 2 3 3 Temperature Separation 14.66 6 7 8 9 9 8 7 6 5 Total Score 174.4 199.3 218.4 233.1 233.1 218.4 203.7 183.2 158.3

Table 5. Orifice Ratio (d/D) design comparison.

Orifice ratio was largely driven by the literature review. While extremely large or small

orifices would be hard to machine, most sizes pose little difficulty. Thermal mass of the system

would be slightly increased with smaller orifice size, but the mass of the spin generator relative

to the overall mass of the vortex tube system is small. The optimal values for orifice size in

Table 5 are 0.4-0.5.

Roughness

More --------- ----------- Less Machinability 10.26 9 8 7 6 Conversion Rate 16.12 1.5 1 1 0.5 Temperature Separation 14.66 6 7 8 9 204.48 200.81 205.21 201.55

Table 6. Roughness design comparison.

Roughness of the tube was interesting to consider for the HVT – in a conventional vortex

tube, the smoother the tube, the lower the losses and the greater the performance. Roughness in a

HVT, however, increases the surface area in the tube for catalyst deposition, and therefore has an

opportunity to increase catalyst activity. Table 6 shows that in our case, a lower surface

roughness will likely still prove to operate better, but that roughness doesn’t necessarily need to

be minimized. The decision was therefore made to manufacture parts without particular attention

to surface finish, but not to intentionally create rougher surfaces on the inside of the tube for

catalyst deposition.

Divergence

35

Yes No Machinability 10.26 5 9 Conversion Rate 16.12 1.5 1 Thermal Mass 4.40 1 1.5 Temperature Separation 14.66 9 6 211.81 203.01

Table 7. Divergence design comparison.

A small degree of tube divergence can create better performance, but also greatly increase the

difficulty of machining. Divergence in the tube also increases surface area inside the tube, and

therefore catalyst area, slightly over a straight tube. A diverging tube will also have slightly less

mass to cool down. The final calculation, shown in Table 7. shows that divergence is a feature

that should be added to the HVT.

Detwister

Yes No Machinability 10.26 7 9 Temperature Separation 14.66 9 6 203.75 180.29

Table 8. Detwister design comparison.

A detwister or flow straightener at the hot end of the tube has shown some benefit, however it

also adds to the machining complexity of the vortex tube. The comparison of values in Table 8.

indicated that a detwister should be added to the HVT design.

Muffler

Yes No Machinability 10.26 1 9 Thermal Mass 4.40 5 9 Temperature Separation 14.66 9 6 164.18 219.89

Table 9. Muffler design comparison.

36

Finally, adding an acoustic muffler to the HVT design was considered. While some

literature has shown an acoustic muffler to improve the performance of a vortex tube, it would be

very difficult to design a proper acoustic muffler for a cryogenic hydrogen vortex tube. The

addition would also add to machining complexity and add significant mass to the system. It was

decided to not include a muffler in the HVT design.

Conclusions from the House of Quality

The results of these comparisons were combined with target values from literature to

obtain the desired goals of a cryogenic vortex tube for this experiment. Based on the conclusions

from this process, the HVT design was conceptualized to be a counter flow vortex tube with 3-6

inlets, an inlet area based off the equations provided by Gao (49), cold orifice ratio of 0.5, have a

length to diameter ratio of at least 20, tube divergence of 2.5 degrees, and contain a detwister at

the hot end.

HVT Design

A final design of the vortex tube was made based on these specifications and is shown in

Figure 9. Hydrogen would flow in through a VCR® - 1/16 NPT adapter (A) into the plenum (B).

A spin generator containing multiple inlets and the cold orifice (C) creates the vorticial flow as it

allows hydrogen to enter the vortex tube. The tube (D) is easily replaceable by removing the

plenum (B) and the hot end fitting (E). At the end of the tube is inserted a cross shaped flow

straightener (not pictured). The hot end fitting (E) is similar in design to the plenum (B), with a

VCR® - 1/16 NPT adapter for the outlet (F). There is no control valve in the design, the cold

flow fraction of the vortex tube is instead controlled by mass flow controllers after the gas exits

the HVT, similar to the design of Metenin (56). The cold gas flowing through the center of the

37

tube flows through the cold orifice in the spin generator (C), and out through the cold end

adapter (G). An optional port was added to the hot end of the vortex tube (H), to allow gas to be

injected into the HVT for a double circuit (or multistage double circuit) design. This injection

port also had a VCR® - 1/16 NPT adapter (I) to connect the HVT to another gas supply. The

injection port (H) could be replaced with a solid plug for tests where a double circuit vortex tube

is not needed.

Figure 9. HVT complete design

The entire vortex tube was to be made out of 6061 aluminum alloy, as aluminum is hydrogen

compatible and will not catalyze the ortho-parahydrogen reaction on its own. The spin generator

and tube sections are easily removed from the design to be replaced with different configurations

for ease of testing different geometries in the HVT. Specifics on the components of the design

are given in the following sections.

Cryogenic Seals:

A major focus of the new vortex tube design was creating a device that could have a gas-

tight seal at cryogenic temperatures. Most fittings used at room temperature are typically difficult

I

A B

C

D

E

F

G H

38

or impossible to seal at cryogenic temperatures, especially when in contact with hydrogen.

Because of this, standard industry practice is to weld connections wherever possible. Keeping the

vortex tube highly configurable meant temporary seals were required, so several seal designs that

have been successfully used in the past were considered.

Metallic crush seals such as the Swagelok VCR® or the ConFlat flange are used extensively

throughout CHEF’s fluid and vacuum systems and are reliable, easy to install, and easy to check

for leaks. The difficulty in application arises from specific dimensions and designs that must be

used in construction. Also, the forces required to crush a metal gasket make using aluminum

difficult, as any threads used for crushing are likely to gall or fail before adequate crushing

pressure on the seal is made. Using VCR® in particular was considered, but the difficulty in

designing around existing fittings and the lack of availability of aluminum VCR fittings led to

this sealing method not being used directly on the HVT.

As has been mentioned earlier in the chapter, NPT seals with PTFE tape have been used

successfully by lab members in the past (60), however, use is usually minimized. Inconsistency

in application of PTFE tape or small damage to NPT threads can lead to small leak paths that

hydrogen can easily navigate. These leaks can be difficult to locate and diagnose as they are

often very small. Nevertheless, the decision was made to use NPT seals with PTFE tape to adapt

the inlet and exit ports on the HVT to VCR®, in order to connect with the rest of the fluid

handling system. Because the HVT is manufactured out of aluminum, stainless steel VCR

connectors could not be welded to the HVT and brazing would have been extremely difficult.

Aluminum’s greater thermal contraction will allow the HVT to shrink around the steel NPT-

VCR® adapter, helping to ensure a good seal.

39

The final sealing tool chosen for the HVT is the indium crush seal. Indium is a malleable metal

that can be easily extruded into wires and films. When this wire or film is crushed, it will deform

to fill any imperfections in the sealing surfaces and extrude to fill any gaps. Indium seals have

been shown to be effective at cryogenic temperatures (67), and will sometimes even cold weld

two surfaces. In designing the indium wire grooves for the HVT, common industry practices

were considered. Common practice says a wire seal should overfill a groove by at least 5-15%

(68, 69). Indium Wire Extrusion recommends the cross sectional area of a square groove to be

80% or less that of the wire (70). The seals in the HVT were designed to be somewhat

conservative at an area 75% that of the cross-sectional area of the wire. Sixteenth inch indium

wire was used in the seals, making the indium seal dimensions 0.0625” wide and 0.003” deep.

Tubes:

The tubes in this design are meant to be easily swappable and allow for removal and

replacement of the tubes easily. Three types of tubes to be tested were selected: a smooth,

conventional tube to get baseline results, a threaded tube to examine the impacts of threading the

tube on vortex tube performance, and a threaded tube coated in catalyst to attempt to cause para-

ortho conversion within the tube. The original tube used to test temperature separation in air was

5mm in internal diameter, based on standard dimensions of commercial vortex tubes designed

for use in air. This was reduced to 3.6mm for hydrogen operations to reduce the use of hydrogen

in the experimental design and allow for longer test times. The threaded tubes were threaded

with a metric 4mm x 0.75 thread, as a custom thread profile was too expensive to machine. This

thread was chosen because its average diameter matched the 3.6mm diameter of the smooth tube.

The length of each tube was 50 diameters.

40

The catalyst used was a ruthenium coating developed by Ultramet, which was the highest

activity single catalyst in previous tests performed by Pedrow (71). A sample tube sent into

Ultramet only received a catalyst loading of 0.005836 kg/m2 ruthenium, and so rifling was used

to increase surface area inside the tube for the catalyst to adhere to. The original design can be

seen in Figure 10a below.

Figure 10a, 10b. The rifled tubes manufactured to increase tube surface area.

When contacting Ultramet about the tube design, it was discovered that their process would be

unable to handle a tube with such a long length, and an alternate tube design was created. This

new tube design, pictured in Figure 10b, has a larger bored hole that can fit tube inserts. Two

tube inserts were created by threading a section of tube, cutting a keyway, and then cutting the

tubes in half. When a key is inserted in the keyway, the proper alignment of the threading is

restored, and the assembly can be inserted in the bored hole of the tube.

Spin Generator Design:

The spin generator is designed using a rectangular slot design that was both predicted by

literature to have good performance (see chapter two), and easy to machine. A cold orifice is

41

drilled in the center, and inlets are dispersed around the edges, as shown in Figure 11. below.

Figure 11. Several generations of spin generator.

The spin generator was intended to be machined out of an insulative material in an attempt to

separate the hot and cold sides of the vortex tube. Initially, the material selected for this job was

Macor®, a machinable glass ceramic with both high insulation value and good machinability.

After machining several Macor® spin generators (right three spin generators in Figure 11.), it

was discovered that sealing them was extremely difficult. While a seal was possible, the line

between enough torque to properly crush the indium seals and so much torque the Macor®

cracked was too thin to be repeatable.

The second attempted replacement material for the spin generator was PTFE, also very

machinable and highly insulative. The PTFE spin generator sealed without issue, however the

compression of the PTFE to generate the seal caused associated expansion in the thickness of the

spin generator, and completely sealed the inlet to the plenum, such that hydrogen could not flow

through the tube.

The third attempt at manufacturing the spin generator utilized 316 stainless steel. This spin

generator had both higher thermal conductivity and was harder to machine than the previous

42

solutions, however the strength was much higher. The stainless-steel spin generator ended up

sealing the vortex tube without issues.

The initial designs for the spin generator had many inlets, with inlet area designed for air

operations so that the vortex tube could be easily tested with compressed air to ensure the vortex

tube was working properly.

Performing a test of the HVT:

Testing started with assembling the HVT in the configuration that was desired to be tested. The

HVT was then attached to a helium line at one of its inlets and the outlets were blocked. The

HVT was pressurized to 60 psia and then submerged in a dewar of liquid nitrogen. This test was

performed to ensure all seals had been properly made and would hold when cycling to cryogenic

temperatures. After removing the HVT from the liquid nitrogen bath, a helium leak check using

a mass spectrometer would be performed to ASTM E499/E499M – 11 Test Method A would be

performed (72). After ensuring the HVT is leak free, it would be installed in CHEF as indicated

at the beginning of this chapter. The whole apparatus is then checked for leaks again following

the same standard. All electrical connections were then verified outside the vacuum chamber to

ensure all temperature sensors, heaters, and hotwires were working properly. Multilayer

insulation was then placed over the cryogenic components of the experiment and the lid to the

vacuum chamber lowered.

Vacuum is pulled on the vacuum chamber initially with a rotary vane pump, until the vacuum

level is measured to be lower than 10-1 Torr. A turbomolecular pump is then switched on and

pulls vacuum down to 10-5 Torr or greater vacuum. Once vacuum has been verified, the first

hydrogen fill can begin. The entire apparatus is pressurized with helium and vented at least three

43

times to ensure no oxygen is left in the system before hydrogen can be introduced. This

pressurization and venting process is then repeated with hydrogen to displace the helium. The

reservoir of the system is left full of hydrogen and the cryocooler on the system is turned on to

begin liquefaction.

While liquefying, the process of filling new hydrogen into the reservoirs is repeated about twice

a day. The liquefaction process takes approximately a week to complete before the experiment is

finally ready for a test, during which the system may not suffer power outage or breakdown of

equipment. In the event something interrupts liquefaction, a safety system is designed with

pressure relief valves sized according to CGA S-1.3 (73) and an emergency vent switch that can

be activated. The fill level of the liquid hydrogen tank is 5 liters of volume, and the test is usually

run at about 4.5 liters. Fill level is tracked by monitoring the pressure of hydrogen in the

reservoir before and after each fill. By calculating the change in mass of hydrogen contained in

the known reservoir volume at each state, an accurate picture of the amount of liquefied

hydrogen can be developed. This is done using code written for the Engineering Equation Solver

(EES) software (74).

When ready to run a test, data collection is turned on in the LabView instrumentation software.

This LabView code has been written to track and record the data from all of the sensors in

CHEF, and also allow for control of the two mass flow controllers. First, hydrogen is allowed to

flow through the mass flow controllers. Once open slightly, hydrogen begins to flow through the

vortex tube and out the vent lines. The heater on the bottom of the liquid hydrogen tank in CHEF

is then turned up to begin boiling the hydrogen and building pressure to the desired pressure

ratio. Once the heater and mass flow controllers have all been verified to be working correctly,

the mass flow controllers are opened all the way to allow the vortex tube to run with minimal

44

backpressure. If a change in flow fraction is necessary, the flow out the hot side mass flow

controller can be reduced to force more flow out the cold side of the vortex tube. Hydrogen is

allowed to cool the system until temperatures approach the desired test inlet temperature. At this

point, heaters are turned on in the reactors to set the inlet hydrogen temperature for the vortex

tube. These heaters are controlled by PID loops in the Lakeshore 336 temperature controller.

Hydrogen is allowed to continue flowing until liquid runs out, at which point the heaters are shut

off, the mass flow controllers closed, and the cryocooler shut off. Full procedures and safety

considerations for the operation of the experiment are given in the Appendix, CHEF Safety Plan.

At least two people are necessary to run all of the equipment, special thanks to Carl Bunge who

helped take the data for this thesis by balancing heater controls manually.

The point at which liquid hydrogen runs out is clearly visible in the data, as the temperature of

the hydrogen in the liquid hydrogen tank starts to rise rapidly and the pressure drops. The steady

state data at the end of the test is used for analysis. Figure 12 below, designed by Carl Bunge,

gives an example of what data from a vortex tube run looks like, along with typical time scales.

45

Figure 12. An example of typical data from a test of the HVT.

Further design details on the construction of CHEF are given in the Appendix, CHEF Design

Documentation.

46

CHAPTER FOUR: RESULTS AND ANALYSIS

The long timescale and challenges of running a complex cryogenic experiment meant that

despite several years of research, only a few test conditions have been successfully operated.

These results show that it is possible to create and operate a cryogenic vortex tube or HVT,

although more data will need to be collected to determine the usefulness of such devices.

HVT Results:

Five tests were successfully completed with the HVT design. A single test measured

performance of the smooth tube – essentially just a cryogenic hydrogen vortex tube. Two further

tests examined the addition of a threaded tube, but no catalyst. These studies were intended to

examine if a vortex tube could be successfully operated with threading on the inside of the tube,

or if this threading would disrupt the vorticial flow and prevent temperature separation. The final

case was two tests with the threaded tube coated in Ultramet Ruthenium catalyst. This final case

was to test if any increase in performance due the the catalyst in the HVT was seen. The results

of the tests are given in Table 10 below.

Table 10. HVT Tests

Test S1U R1U R2U R1C R2C Tube Smooth Tube Threaded Tube Threaded Tube Threaded Tube Threaded Tube

Catalyst None None None ULTRAMET Ruthenium

ULTRAMET Ruthenium

Pressure Ratio 2.00±0.05 1.79±0.04 1.93±0.05 1.83±0.04 1.96±0.05 Cold Fraction 0.372±0.003 0.37±0.003 0.44±0.004 0.382±0.003 0.421±0.003 Cold Temp Drop 0.83±0.35 K 1.07±0.35 K 0.51±0.35 K 1.50±0.35 K 1.70±0.35 K

Hot Temp Rise 2.50±0.35 K 2.02±0.35 K 1.63±0.35 K 2.06±0.35 K 1.13±0.35 K

47

Error Analysis and Uncertainty:

Uncertainty of each of the instruments was collected and measured to determine error of

the measured values. Instrumental errors are given below in Table 11. All temperature sensor

error was calculated using quoted error values from Lakeshore Cryotronics using their SoftCal

method to create a two-point calibration valid to 70 Kelvin using a room temperature control

point and a control point set by liquid nitrogen at it’s boiling point in atmospheric pressure. It

should be noted that Carl Bunge performed a full calibration of the sensors following this

experiment using Lakeshore Cryotronics calibrated germanium and Cernox sensors as controls.

Uncertainty of the new calibration was determined to be ±53 mK. The SoftCal was found to

measure 0.54 Kelvin low for the inlet temperature sensor and 2.85 Kelvin high on the vortex tube

hot side temperature when compared to the new calibrated values for this range. The vortex tube

cold side temperature SoftCal measurement agreed with the new calibrated measurement within

0.08 Kelvin for the entire range of measured values.

Type Model Number Accuracy Reproducibility Zero/Span Shift Total Bias Units Platinum RTD PT-111 0.25 0.005 - 0.25 K

Piezoresistive Transducer

Keller America Valueline (200psia)

- - - 0.5 psia

Piezoresistive Transducer

Keller America Valueline (100psia)

- - - 0.25 psia

Transducer Paroscientific 0.001 - - 0.001 psia Laminar Pressure Based Flow Meter

Alicat MCR-100SLPM-D/5M

0.02 + 0.008 * reading

0.2 0.02 Reading dependent SLPM

Table 11. Errors associated with experimental equipment.

Random uncertainty error was taken from 31 measurements immediately before liquid hydrogen

ran out and conditions in the experiment changed. Temperature values measured for each test

48

varied by less than one tenth Kelvin per minute over the sampling period, except test R1C, which

varied by 0.16 K/min. The 31 values were averaged and standard deviation calculated, as given

in Equation 8, with xi as each individual data point indexed from i=1 to i=31 and the algebraic

mean given as !.

#$ = &'(!) − !),

(30)

/0

)10

2

0,

8

A 95% confidence interval, Pr was then generated according to Equation 9, using the Student’s t

distribution value of t=2.042 for 30 degrees of freedom.

45 = ±7#$√30

9

Total error was calculated as the geometric mean of the total error of the instruments as well as

the random uncertainty of the measurements. Error propagation was calculated using the

Engineering Equation Solver (EES) Uncertainty Propagation calculator (74).

49

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS

Conclusions from this research:

This work has shown that the Heisenberg Vortex Tube can be constructed and that it can

be operated at cryogenic temperatures with hydrogen gas. Design considerations were discussed

and a working design proposed and tested. The results show clear temperature separation was

achieved, even at low pressure ratios. It is difficult to draw further conclusions from the data

collected, as only a few data points could be collected, however a few interesting observations

can be made:

Comparing test S1U and R1U, we can see that despite a lower pressure ratio, the threaded test

achieved a higher temperature drop with other conditions similar. This indicates that the

threading in the tube is not disrupting the temperature separation in the vortex tube and may

actually be helping to promote continued vorticial flow. R2U does not show this same trend but

has a higher cold fraction for the test. A higher cold fraction would likely drop temperature

performance, as more gas needs to be cooled with less gas to transfer the energy to.

Tests R1U and R1C have pressure ratio and cold fraction that are quite similar, and the catalyzed

test does show cooler temperatures on both the hot and cold exits of the flow. This would be

expected if the HVT is working and achieving catalyzation of the hydrogen flow, however this

result is not outside of error so could be entirely the result of measurement inaccuracies.

Tests R2U and R2C likewise have very similar pressure ratio and cold fraction, and again we see

increased cooling of both the hot and cool exit streams. In this case, the cooling that occurs on

the cold exit stream is outside of measurement error, although the reduction in heating on the hot

stream is not.

50

All 5 data points measured agree well with theoretical expectations for the measurements. While

a theoretical analysis of vortex tube performance was not completed as part of this work,

theoretical predictions and comparisons to the data in this work can be seen in work by Carl

Bunge (75).

In general, with only 5 data points so far, little can be said for the repeatability of these

measurements. While all tests clearly show temperature separation outside of errors in

measurements, there is little conclusive evidence to the effectiveness of the HVT. Further work

should be done to repeat these measurements and measurements at higher pressure ratios will

help to move measurements outside the realm of experimental error.

Recommendations for future research:

While the design, manufacture, and operation of a cryogenic vortex tube has now been

shown, continued research and development work for such systems is needed to fully realize the

potential benefits. A real understanding of the performance of cryogenic vortex tubes requires

data detailing the impact of numerous parameters of operation: varied geometric parameters,

operating conditions, and a range of cryogenic fluids. In the best case, this will require several

data points at differing configurations that can be used to create a verified and validated

computational fluid dynamics model with real fluid properties. Full understanding of vortex tube

potential may require years of additional data to examine operating conditions that are difficult to

model.

Specific advances can also be made to the design and manufacturing of the vortex tube in future

generations. Some of these have already begun at the HYPER lab, while others I will mention

51

here in the hopes the engineering work can be accomplished in the near future. In no particular

order, I’ll detail below.

The HVT concept is reliant on effective catalyzation of the hydrogen from parahydrogen to

orthohydrogen. More catalyst studies examining both new types of catalysts and new ways to

apply them will always be needed to improve performance.

The vortex tube geometry can be better designed for cryogenic applications. Fewer seals and less

mass are always good things when operating a cryogenic experiment. An example of this kind of

design is one that integrates the spin generator into the tube of the vortex tube. I believe a design

reducing the part count to two is possible if the vortex tube is not constructed with part

interchangeability in mind. 3D printing may be a good option to continue to advance the designs

of vortex tubes. Complex geometries can then be manufactured with very low mass and no

sealing surfaces.

52

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57. Saidi MH, Valipour MS. Experimental modeling of vortex tube refrigerator. Applied Thermal Engineering. 2003;23(15):1971-80.

58. Sh. A. Piralishvili aVMP. Flow and Thermodynamic Characteristics of Energy Separation in a Double-Circuit Vortex Tube - An Experimental Investigation. Elsevier Science Inc. 1996;12:399-410.

59. Liu JY, Gong MQ, Wu JF, Cao Y, Luo EC. Chapter 36 - An experimental research on a small flow vortex tube at low temperature ranges. Proceedings of the Twentieth International Cryogenic Engineering Conference (ICEC20). Oxford: Elsevier Science; 2005. p. 165-8.

60. Bliesner RM. Parahydrogen-orthohydrogen conversion for boil-off reduction from space stage fuel systems. Washington State University. School of M, Materials E, editors. Pullman, Washington]: Thesis (M.S.)--Washington State University,2013.; 2013.

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61. International Electrotechnical Commission. Industrial platinum resistance thermometers and platinum temperature sensors. Geneva: IEC; 2008.

62. Lakeshore Cryotronics. Technical Specifications - Platinum RTDs 2018 [Available from: https://www.lakeshore.com/products/Cryogenic-Temperature-Sensors/Platinum-RTDs/Models/pages/Specifications.aspx.

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APPENDIX

58

CHEF Safety Plan

Revision Information:

This revision prepared for during the construction / addition of the vortex experiment to

CHEF. Prepared for the running of cryogenic vortex tube experimentation. This document was

implemented largely based off feedback from the Department of Energy (DOE) Hydrogen Safety

Panel. The date of last revision is Saturday, February 17, 2018. The last revision was prepared by

Elijah Shoemake. Authors are Carl Bunge, Jacob Leachman, Elijah Shoemake

Scope

This safety plan was developed following the Department of Energy “Safety Planning for

Hydrogen Fuel Cell Projects” document available on-line at:

http://energy.gov/sites/prod/files/2014/03/f10/safety_guidance.pdf

Background Information

STATEMENT OF PURPOSE:

The goal of this experiment is to perform a bench-top scale test of the vortex tube at cryogenic

temperatures and with hydrogen. Our goals are to validate our first order models for cryogenic

hydrogen vortex tube performance, and to get test results comparing uncatalyzed hydrogen

performance with tube performance showing a 5% difference in catalysation. The current project

is conducted in collaboration with the National Renewable Energy Lab

WSU LABORATORY SAFETY POLICIES AND PROCEDURES:

All experiments at WSU are advised to have a safety plan within a printed notebook next to the

experiment. This notebook is in addition to the laboratory safety and chemical hygiene plan on

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the laboratory website and HYPERDRIVE. It is recommended that this safety plan be revised

whenever extensive modifications occur to the experiment and at least annually.

WSU Environmental Health and Safety provides guidance on the development of safety plans.

WSU Environmental Health & Safety (EH&S) maintains an on-line laboratory safety manual at:

https://ehs.wsu.edu/labsafety/LabSafetyManual.html. A list of 1-page helpful fact-sheets is

available at: https://ehs.wsu.edu/training/EHS-Factsheets.html. Both are also available on the

laboratory website. Shawn Ringo is currently the head person in this area and has been involved

in this project. Safety evaluations and audits are conducted annually by the Experimental and

Laboratory Safety Committee within the School of Mechanical and Materials Engineering. Dr.

Leachman is currently a member of the committee.

WSU GENERAL WORKPLACE SAFETY 3.80: COMPRESSED GAS CYLINDERS AND

GAS DISTRIBUTION SYSTEMS

The WSU Compressed Gas Cylinder and Gas Distribution Systems section in the WSU Safety

Policies and Procedures manual outlines important guidelines and regulations regarding the

handling of compressed gas systems. Experiment operators should be aware of these policies and

procedures and understand how to properly implement/follow them.

HISTORY OF CHEF:

The Cryocatalysis Hydrogen Experiment Facility (CHEF) was originally developed in 2012 to

investigate the performance of cryogenic catalysts for Parahydrogen-orthohydrogen conversion.

The experiment liquefies (<5L) hydrogen and converts to the parahydrogen form before flowing

through a catalyst bed and over a calibrated hot-wire para-ortho composition cell. The first

version of the experiment was constructed of brass NPT pipe fittings and operated for ~6 months

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and approximately 10 cycles. Ron Bliesner received his Master of Science (MS) degree in

mechanical engineering in 2012 for developing CHEF and is now employed at Blue Origin in

Kent, WA.

In the fall of 2014 the experiment was refurbished with primarily welded stainless steel plumbing

within the cryostat and two additional catalyst beds were added with a change to a vertical

orientation. This change allowed characterization of deposited Ruthenium-Iron-Oxides for para-

orthohydrogen conversion. This experiment functioned for ~15 cycles until February of 2016

when it was transformed into the current configuration. Brandt Pedrow received a Master of

Science (MS) degree in 2016 for the refurbishing and catalyst blanket tests and is now also

employed at Blue Origin.

The current configuration of CHEF removes one of the catalyst beds and in-place is a cryogenic

compatible vortex-tube. The vortex tube is coated with a catalytic material for para-

orthohydrogen conversion on the outer wall. During a routine test in July, a power outage

occurred within 10 minutes of a planned test, with maximum liquid hydrogen fill. The details are

provided elsewhere: https://hydrogen.wsu.edu/2016/08/15/our-near-miss-hydrogen-vent-in-etrl-

221/ The Hydrogen Safety Panel, an independent organization flew out Nick Barilo (PNNL) and

David Farese (Air Products) to review the events leading up to the vent and provide

recommendations. The resulting analysis uncovered the need for several improvements to the

operating procedure, building capability, and general safety plans, including this safety plan

document. Elijah Shoemake and Carl Bunge are working toward their Ph.D. degrees with CHEF.

National Renewable Energy Laboratory (NREL) specifically with Chris Ainscough as the PI.

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Operating Procedures

There are many operations that must be performed to operate CHEF. The procedures for

the most routine operations are provided here: 4.2. Liquefaction Procedure, 4.3. Warm-Up

Procedure, and 4.4. Emergency Procedure. Following each valve name is a bolded number in

brackets ([#]), each valve on the pegboard is labeled with both a name and this number for clarity

and ease of operation.

NOTES TO THE OPERATOR:

There are many little things in operating CHEF that may be counterintuitive or seem unusual.

Here are some insights from past operations:

Check valves, especially those built into the flame arrestors on CHEF (and the hydrogen

regulator) will make a buzzing or clacking sound at low pressure differentials. This is normal.

LIQUEFACTION PROCEDURE:

Use mass spectrometer with helium to check for leaks in system, following ASTM E499/E499M

– 11 Test Method A:

Pressurize with helium to the test pressure of 60 psia, then purge by opening the purge valve [1].

Close the purge valve [1] and repeat two more times. Leave 60 psia helium in the system.

Sniff all fittings, welds, and solder joints with mass spectrometer by passing the sniffer probe

over likely leak points. Start at the bottom of the assembly and work your way up, holding the

probe on or not more than 1mm from the surface. Do not move the probe faster than 20mm/s.

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Continue sniffing in an orderly procedure from bottom to top. Mark any leaks so they can be

remedied. Be aware that helium will rise, so a leak above a previously found leak may not

actually exist. It is also important to be aware of the airflow in the room, as helium can be blown

around the experiment and produce small “leaks” that don’t exist.

If any leaks are identified, take corrective action and restart this procedure.

Leave positive pressure helium in system.

Replace cap on inlet line after removing helium gas line.

Verify all electrical connections are nominal.

Complete pinout checks on both D-sub connectors located on the exterior of CHEF with

ohmmeter and designated CHEF breakout board.

Ensure all electrical routes are clear from the inner stage MLI shield tie down points.

Place MLI shield over experiment.

Ensure gloves are worn to prevent oils from accumulating on the MLI material.

Affix inner stage MLI shield by bolting down to 1st stage cryocooler base-plate and attach

braided thermal straps.

Ensure all electrical connections are working properly by checking the Lakeshore readouts, it is

also acceptable to repeat the pinout check above.

Place outer stage of MLI shield over the inner stage. Use care not to allow the blanket to catch or

rip while sliding into place.

Close vacuum chamber. Close vac. relief valve located on the top of the vacuum chamber.

Start roughing pump.

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The D60A can be used to pull down initial vacuum, but cannot be used with hydrogen service.

The maximum pumping capacity for hydrogen service in CHEF is 11.7cfm to prevent more than

a 60% LFL concentration from being possible in the vent hood.

Ensure turbomolecular pump is off and turbo vent valve is closed using Agilent T-plus software

on the CHEF computer.

Watch for falling system pressure as well as overall vacuum level to look for new leaks.

When vacuum level reaches 10-1 Torr without leaks, start turbomolecular pump.

Watch vacuum level to ensure it reaches 10-5 Torr range (the nominal vacuum range of CHEF

without cryocooler operating).

If system appears leak tight, begin hydrogen fill process.

When working with hydrogen, wear flame resistant lab coat. These are the blue lab coats

hanging on the laboratory coat hook.

If using the D60A to pull down initial vacuum, switch to a smaller roughing pump before filling

with hydrogen. The maximum pumping capacity for hydrogen service in CHEF is 11.7cfm to

prevent more than a 60% LFL concentration from being possible in the vent hood. The D8B or

similar sized roughing pump is well within this service range (maximum 6.9cfm).

Use grounding cable (red clamp labeled Ground) to electrically ground the hydrogen bottle.

Attach hydrogen bottle.

Ensure meter valve [2] is fully open.

Vent inert gas by opening condenser shutoff valve [3] and condenser manual vent valve [7].

Close condenser manual vent valve [7].

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Open gas in valve [4] and fill valve [5], pressurize to 60 psia hydrogen. Close gas in valve [4].

Vent by opening purge valve [1]. Close purge valve [1]. Repeat two more times.

Close condenser shutoff valve [3], meter valve [2], and fill valve [5].

Open reservoir shutoff valve [6].

Pressurize gas reservoir to ~60 psig

Set regulator pressure to 60 psi

Open regulator needle valve slowly, and use valve to control pressurization rate.

Close bottle valve when complete.

Close reservoir shutoff valve [6].

Depressurize by opening purge valve [1] and gas in valve [4].

Close purge valve [1] and gas in valve [4].

Remove hydrogen bottle and detach ground cable.

Store hydrogen bottle in bottle closet. Replace cap on gas inlet line.

Open reservoir shutoff valve [6] and condenser shutoff valve [3].

Use meter valve [2] to control fill rate.

Monitor vacuum level for leaks.

If system appears leak tight, begin hydrogen fill process.

When working with hydrogen, wear flame resistant lab coat. These are the blue lab coats

hanging on the laboratory coat hook.

Use grounding cable (red clamp labeled Ground) to electrically ground the hydrogen bottle.

Close off valve [3] to the condenser.

Close valve [6] to the reservoir.

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Record reservoir pressure, Condenser temperature, and vacuum level in the word test report.

Use the hydrogen regulator to connect to the hydrogen bottle and tighten with 1-1/8th inch

wrench. NOTE: The threads are reversed!!!

Make sure the regulator is closed (all the way out) and the regulator needle valve is closed.

Make sure valve [4] is closed at this time.

Unscrew the compression fitting cap to prepare the attachment of the hydrogen regulator line.

NOTE: This short section upstream of valve [4] does not contain pressure/hydrogen.

Attach hydrogen bottle to experiment via compression fitting at gas inlet port near valve [4].

NOTE: Be mindful not to induce unnecessary stress on the brass fitting. If damaged replace

before the fill.

Ensure valves [1,3,5,6] are closed at this time.

Open main hydrogen bottle valve and inspect the bottle pressure to ensure enough hydrogen is

available to complete a fill. Else keep regulator all the way out and close main bottle valve.

There is minimal hydrogen in this short section and it safe to dissipate (slowly) by unscrewing

main regulator with 1-1/8” wrench.

Vent air in regulator lines by opening valve [4] and pressurizing to 60 psia via the regulator and

opening the needle valve.

Proceed to purge by closing valve [4]. Vent by opening purge valve [1]. Close purge valve [1].

Repeat two more times.

Open reservoir shutoff valve [6] and open valve [5].

Close needle valve on regulator.

Open Labview and inspect reservoir pressure.

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Increase regulator pressure to ~90psia, then open valve [4] and slowly open the needle valve to

begin the fill.

Once gas reservoir has reached ~85 psia by checking the labview readout:

Close the needle valve.

Record reservoir pressure in word test report. Save report.

Close reservoir shutoff valve [6] and fill valve [5].

Close main fill bottle valve.

Depressurize regulator opening purge valve [1] and regulator needle valve. Visually confirm that

the regulator is depressurized by look at the regulator gauges. NOTE: Tap gauges if need be.

Close purge valve [1] and gas in valve [4].

Back out regulator valve and shut needle valve.

Remove hydrogen bottle compression fitting near the gas inlet valve [4].

Replace cap on the experiment fill port.

Remove regulator with 1-1/8” wrench. NOTE: Righty loosen!!!

Detach ground cable and replace cap.

Store hydrogen bottle in bottle closet.

Open reservoir shutoff valve [6] and condenser shutoff valve [3].

Adjust (If need be) the meter valve [2] to control fill rate to ensure no thermal shock occurs.

Monitor vacuum level for leaks.

Begin process to turn on cryocooler.

Ensure vacuum level remains in the 10-5 Torr range

Make sure building water supply and return lines are open.

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Visually inspect the cooling loop filter for excessive debris. Ensure the filter has been replaced

according to the maintenance schedule (monthly).

Turn on water cooling loop pump.

Ensure water cooling loop valves located on the hoses connecting the cooling loop to CHEF’s

cryocooler are open.

Turn on cryocooler.

Begin taking “continuous data” in LabVIEW by pressing the large toggle button in the CHEF

Monitor located below the plot legend.

Allow cryocooler to drop temperature to ~20 K.

STANDARD FILL PROCESS:

When working with hydrogen, wear flame resistant lab coat. These are the blue lab coats

hanging on the laboratory coat hook.

When reservoir pressure drops to near 60 psig (or higher), fill with hydrogen. Repeat this fill

cycle until 4L of hydrogen is liquefied.

Track your fill process using the FillCode_revC, and record on the test report:

Open newest FillCode_revX found under H:\CHEF\Operating Manual:

Next, open the test report template (CHEFTestReport_yearmmdd.docx) under

H:\CHEF\Operating Manual\Test Reports

A single fill line will consist of data prior to fill designated by “Pre” and after fill designated by

“Post”.

NOTE: Ensure all Post fill data has reached steady state (Post T & Post V) before recording.

Cell A: Reservoir pressure before fill.

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Cell B: Reservoir pressure after fill.

Cell C: Liquefier temperature prior to fill.

Cell D: Liquefier temperature after fill.

Cell E: Vacuum level prior to fill.

Cell F: Vacuum level after fill.

Cell G: Total volume of para-hydrogen in liquefier at 20K if entire contents of the reservoir were

liquefied. This provides a conservative estimate and projected fluid volume ~24hrs in the future.

Cell H: Mass of hydrogen added for the individual fill.

Cell I: Total volume of liquid para-hydrogen in liquefier at 20K if entire contents of the reservoir

were liquefied. This provides a conservative estimate and projected fluid mass ~24hrs in the

future.

Record cells A, C, and E from LabVIEW.

Repeat following steps as necessary until necessary liquefaction level is acquired to run the test:

Wear Nomex fire proof lab coat and face shield.

Prop open ETRL 221 lab door with door stop to avoid unnecessary maneuvers with bottle cart.

Retrieve hydrogen bottle in gas bottle closet (ETRL 219) with bottle cart. Ensure bottle cap is

tight and safety chain is fastened before moving bottle.

Position cart such that hydrogen bottle is roughly in line with CHEF’s reservoir bottles.

NOTE: Small adjustments may be needed to fine tune the docking of the copper line from the

regulator to the CHEF fill port attached to gas in valve [4].

Remove safety cap from hydrogen bottle. Set aside.

Use grounding cable (red clamp labeled “Ground”) to electrically ground the hydrogen bottle.

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Find the hydrogen fill regulator located on the window sill behind CHEF.

Use a 1-1/8” wrench to tighten the regulator onto the bottle.

NOTE: The threads of a flammable gas regulator and bottle are reversed. Ensure a snug tight fit

but do not over tighten the regulator.

Ensure gas in valve [4] is in the off position.

Remove the fill port cap attached to gas in valve [4] using a ½” and 9/16” wrench.

Inspect threads of the fill port. Replace if needed.

Next, ensure all grounding connections are nominal.

Connect the copper line from the regulator to the fill port.

NOTE: Tighten using two wrenches until snug. Beware of over tightening.

Close condenser shutoff valve [3] located next to the meter valve in the middle, right of the peg

board.

Close the reservoir shutoff valve [6] located just above the peg board near the reservoir manifold.

Next, we are going to purge the small amount of air which was entrained in the regulator line

upon connection:

Ensure the regulator is shut at the main valve (unscrewed is closed) and the needle valve attached

to the regulator is also closed.

Carefully open the main bottle valve approximately 1 rotation.

----↓Repeat following purge procedure until 3 purge cycles are complete↓ ----

Ensure valves [5], [1], [3], [6], [7], and [4] are closed.

Open gas in valve [4] at a normal pace.

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NOTE: On the first purge cycle, there will be a flammable mixture present in the line for a

fraction of a second. This is not to be fretted over since we have ensured that there are no

ignition sources and the entire system is grounded to prevent static discharge.

With the needle valve on the regulator closed, begin to screw in the regulator valve until 80 psi

gauge is showing on the bottle regulator.

Slowly crack to the needle valve on the regulator to avoid a pressure impulse by watching gauge

on regulator.

Allow pressure to equalize at 80 psi gauge.

To prepare for the next purge, shut the needle valve on the regulator.

Close gas in valve [4] now that we have charged the system for our first purge.

Complete this purge by opening purge valve [1].

NOTE: You may hear a chatter from the check valve downstream from the this valve. This is

normal.

After the audible sound of gas whooshing past the valve ceases, close purge valve [1].

Repeat the previous 9 bullet points until 3 cycles are complete to ensure all air is evacuated from

the system.

--------------------------------- ↑Purge Procedure↑ -----------------------------------------

After the third purge ensure gas in valve [4] is closed.

Open reservoir shutoff valve [6] near the reservoir manifold to prepare to fill the reservoir tanks.

With the regulator needle valve closed, double check that the regulator reads 80 psi gauge.

Open gas in valve [4].

Open fill valve [5].

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NOTE: Residual from the fill line will introduce some hydrogen into the tanks upon opening this

valve. Again, the check valve may be heard which is normal.

Slowly crack the needle valve on the regulator and use this valve to achieve a steady fill rate into

the reservoir tanks.

NOTE: There may be resonance at lower flow rates. Increase flow rate to bypass this region by

opening the needle valve on the regulator further. In the extremely rare case that the regulator

fails and just starts gushing. Stay calm. There are integrated pressure reliefs on both the reservoir

and regulator.

Once an audible equilibrium has been achieved check the LabVIEW program to see the psia

level on the liquefier. It should read around 78 psia.

Now, we will begin the disconnect process:

Close reservoir shutoff valve [6].

Close the fill bottle main valve

Close fill valve [5].

Ensure the regulator needle valve is closed and regulator itself is open.

Open purge valve [1].

Depressurize fill lines and regulator by slowly open regulator needle valve.

Close purge valve [1].

Close gas in valve [4].

Close the regulator needle valve and unscrew the regulator main valve until closed.

Remove hydrogen bottle regulator copper line from the fill port using two wrenches.

72

NOTE: Do not be alarmed by a slight back pressure upon the disconnect of the line. This tiny

amount of hydrogen is quickly dissipated in the air and is not a hazard.

Remove regulator from the hydrogen fill bottle and place back on window sill.

Replace cap on the fill port attached to gas in valve [4].

Detach ground cable from bottle and reattach to the aluminum bosch frame.

Replace safety cap on hydrogen fill bottle.

Use cart to return hydrogen bottle to bottle closet.

Last step is to reconnect the reservoir to the liquefier on CHEF:

Open reservoir shutoff valve [6].

Open condenser shutoff valve [3] delicately while simultaneously watching the LabVIEW

liquefier temperature readout.

NOTE: If there is a spike in temperature, close this valve and fine tune the needle valve.

However, see the next section for setting the needle valve. It should not need to be adjusted once

set.

Ensure proper fine tuning of meter valve [2] by also watching the liquefier temperature to control

fill rate.

NOTE: This is a finely tuned needle valve which allows for a constant cryopump effect and

steady liquefaction. Be sure to tune to allow a very small flow rate into the liquefier. This takes

patience.

Monitor vacuum level for leaks.

NOTE: Small increases are acceptable (likely due to thermal events, not leaks), but do not

exceed 5 x 10-4 torr. If pressure seems to be rising quickly, use meter valve [2] to lower the fill

73

rate. If vacuum level continues to rise after condenser temperature equalizes, there is likely a

significant leak in the system.

The last thing to do is record the post fill data and calculate the amount of hydrogen introduced

to the system:

Reopen the CHEF Test Report and input Cells B, D, and F.

NOTE: This may take a while for temperatures to equilibrate.

Using Cells A and B use the FillCode_revX to calculate cells G, H, and I.

Approximately 8 fill cycles should be expected, depending on the pressures at which CHEF is

refilled and the rate of liquefaction.

VORTEX TUBE RUN PROCEDURE:

Begin cool down of the vortex tube:

Open hot end ball valve.

Set hot end Alicat MFC to 5 SLPM – Set to 1 in the LabVIEW dashboard.

Open cold end ball valve.

Set cold end Alicat MFC to 5 SLPM – Set to 1 in the LabVIEW dashboard.

Verify both Alicats are allowing the correct amount of flow out of the experiment.

Turn on condenser heater to ~100V using the Variac.

Set both Alicat MFCs to maximum flow, 20 in the LabVIEW dashboard.

Hold pressure at 30 psia in the condenser by using the Variac to adjust the heat loads on the

condenser.

Wait 10 minutes or until VT Inlet temperature sensor is close to 77K.

74

While waiting, connect HW power boards and verify that they are powered and working by the

LED lights turning on.

After HW power boards are confirmed to be working, plug in HW wires and press the reset

button if necessary.

Ramp up the pressure in the condenser by increasing the voltage of the condenser heater variac

until the pressure ratio across the vortex tube is 4.

Turn on the reactor heater PID controls, set to HIGH (Should be set to 50% base power, and PID

control).

As the tube begins to cool, prepare the reactor heaters to maintain 77K through the tube.

Plug in Hotwire heater Variacs, and adjust to hold temperature at 130 K. Do this slowly to avoid

hotwire damage.

Set hot end Alicat MFC to get desired flow fraction. (~ cold flow fraction of 0.2)

Turn up voltage on the condenser Variac to keep pressure at the desired pressure ratio.

Monitor vortex tube temperature, wait for steady state conditions.

Take data at steady state.

Adjust to new flow fraction (~ 0.4 or next parameter to be tested next)

Wait for steady state

Take data at steady state.

Repeat as necessary

Once a sharp increase in liquefier pressure is witnessed, turn off the Variac condenser heater and

Alicat flow meters with ball valves.

Purge with helium and begin warm up.

75

1.4. WARM-UP PROCEDURE:

Open condenser shutoff valve [3] and meter valve [2].

Manually vent the hydrogen gas through the room vent line by opening the purge valve [1].

Leave open until liquid is gone.

Vaporize remaining liquid hydrogen by increasing condenser heater power to 90 volts via Variac

controller until temperature increase of 0.5 K is observed on the temperature monitor. Monitor

the temperature as CHEF warms up, and turn off the heater if temperatures rise above 280 K.

Close purge valve [1].

Manually shut off the cryocooler.

If no one else has a cryocooler on, you can turn off the water cooling loop and the building water

supply. DO NOT SHUT OFF THE COOLING WATER IF ANOTHER CRYOCOOLER IS

RUNNING.

Open fill valve [5] to ensure that any remaining hydrogen expands into the gas reservoir as

CHEF continues to warm.

Allow everything to warm up to room temperature.

Note: Condenser heater may be used to speed up heating process, but Reactor or Hotwire heaters

should NOT be used.

Open purge valve [1] to purge any pressure that has built up in the system. Close the purge valve

[1].

Attach a helium bottle to purge the system.

Close condenser shutoff valve [3], meter valve [2], fill valve [5], and reservoir shutoff valve [6].

76

Open gas in valve [4], pressurize to 60 psi helium. Close gas in valve [4]. Vent by opening purge

valve [1]. Close purge valve [1]. Repeat two more times.

The regulator line should now be purged of air.

Open meter valve [2] fully, and open reservoir shutoff valve [6].

Pressurize with helium to the test pressure of 60 psia, then purge by:

Open gas in valve [4]. Ensure regulator is set to ~60 psia.

Close gas in valve [4] when pressure reaches 60psia.

Open the purge valve [1]. Close the purge valve [1]

Repeat two more times. Leave ~10 psia helium in the system.

When lowest temperature reading is above 285 Kelvin, you may shut off the vacuum and

gradually open the vac. relief valve on the top of the vacuum chamber to achieve audible air

flowing into the experiment. Leave this valve open until ready to run again.

Leave CHEF’s vacuum chamber closed when not in use to keep it clean and prevent accidental

damage.

EMERGENCY PROCEDURE:

The system is completely autonomous and will passivate itself without any intervention. The

Uninterruptable Power Supply (UPS) will maintain power for an estimated 60 minutes to the

Alicat flow meters, Lakeshore temperature controllers, data acquisition board, CHEF computer,

and pressure transducers. Preserve the liquefaction progress by following these

recommendations:

77

Do not activate the EMERGENCY STOP unless you perceive a risk to equipment and personnel.

In most cases, an EMERGENCY STOP is not necessary unless it is believed that hydrogen is

leaking into the room.

The primary pressure relief system will activate at 145 psi to maintain pressure regardless of the

state of the UPS.

All the hydrogen will vent out the roof vent line.

If you believe hydrogen is leaking into the room, or you believe any personnel are in immediate

danger, follow the emergency abort procedures below.

IN CASE OF HYDROGEN LEAK INTO THE ROOM:

Follow the emergency abort procedures below by pressing the EMERGENCY STOP button.

Evacuate all personnel immediately and pull the fire alarm.

IN CASE OF HYDROGEN LEAK INTO THE VACUUM CHAMBER:

In the event that hydrogen leaks into the vacuum chamber, it should be immediately visible by an

increase in vacuum chamber pressure. In most cases, this leak will be small enough that the

vacuum will suck any hydrogen out and vent into the hood system. The system can be safed by

venting all hydrogen and purging with helium, then following the standard warm up procedure.

If vacuum pressure rises above 5 x 10-2 Torr, you believe hydrogen is leaking into the room, or

you believe any personnel are in immediate danger, follow the emergency abort procedures

below.

EMERGENCY ABORT:

Press the red illuminated EMERGENCY STOP button located above the Lakeshore temperature

monitors.

78

If you believe that hydrogen is leaking into the room, evacuate immediately and pull the fire

alarm.

Management of Change Procedures

In order to make changes to CHEF, the following procedures and documentation must be

developed, reviewed, and approved prior to implementing the change. When a change is

proposed, it is necessary to review the Safety Failure/Hazards matrix and the operational

procedures section of this report to make sure no new hazards have been created and that

operational procedures remain current. This section also contains information on the

maintenance of equipment along with dates and estimated performance.

MANAGEMENT OF CHANGE PROCESS:

1. A need to change CHEF is identified.

2. The change is discussed with at least two knowledgeable members of the lab to get a

second opinion on the necessity of the change. Details of what should be changed and how are

discussed.

3. A proposal for change is created, stating the need for change and details of what the

change will include. This proposal will include:

a. relevant engineering standards,

b. necessary sizing calculations,

c. details of implementation of the change, and

d. how the change affects this document, including Safety Failure/Hazards matrix and

operating procedures.

79

4. The full proposal is discussed with the PI and experiment operators. If it is agreed upon

the details of the change, the change is implemented, otherwise the change is discarded or is re-

designed. The PI has the final decision on approval.

5. Implement the changes. Document these changes (i.e. the proposal) in the CHEF folder

on HYPERDRIVE or on the CHEF website for future reference. Communicate the

implementation and completion of the changes with others in the lab through the proper lab

Slack Channel.

6. If procedures are affected by the change, update this document with new operating

procedures. Detail any changes or updates to the document in the changelog at the end of the

document.

7. If new maintenance / safety concerns arise from the change, note them in the proper areas

in this document.

MANAGEMENT OF NEW PRIMARY OPERATORS:

1. Have the new operator read the history and documentation on the CHEF folder of

HYPERDRIVE. They should familiarize themselves with what has been accomplished with

CHEF in the past, and how the experiment is currently set up.

2. Give the new primary operator this document so they can familiarize themselves with the

scope of the experiment, potential safety issues with its operation, current operating procedures,

and required maintenance issues.

3. Establish a multi-week mentor program to train the new primary CHEF operator on

emergency, leak check, liquefying, experimentation, and warming up scenarios and procedures.

Have the mentee show the existing primary operator all steps for each scenario.

80

MAINTENANCE AND REPAIR SCHEDULE:

The maintenance and repair schedule will be kept in the CHEF work-log as a sub-tab in the

Excel file labeled ‘CHEF Log_rev[X]’ in the CHEF folder of the HYPERDRIVE. This

workbook keeps track of the CHEF experiment including the history projects and total time

elapsed on individual components. This workbook also tracks the total funds spent on

maintenance parts, hydrogen gas, and experimental updates. A recommended maintenance

schedule in the document tracks required periodic maintenance. This excel file adds visibility to

the CHEF experiment and allows for a predictive model to diagnose and prevent issues caused

by thermal cycling.

81

CHEF Design Documentation

Revision Information:

This revision prepared for during the construction / addition of the vortex experiment to CHEF.

Prepared for the running of cryogenic vortex tube experimentation. Last date of revision is

Friday, April 20, 2018. Last revision was prepared by Carl Bunge and Elijah Shoemake. Authors

of the document include Carl Bunge, Brandt Pedrow and Elijah Shoemake.

Electrical

This section details the electrical systems in CHEF. Pinouts for connections, wiring

diagrams, and wiring label guides are given here. Data on the electrical equipment is also given.

If you are looking for software, calibration information, or details on reading the sensors, look in

section 4 instead.

bäÉÅíêáÅ~ä=cÉÉÇíÜêçìÖÜ=NW=qÉãéÉê~íìêÉ=pÉåëçêë=

máå= pÉåëçê= páÖå~ä=N= eçí=eçíïáêÉ=qÉãé= =O=

sçêíÉñ=fåäÉí=sçäí~ÖÉ=içï=EJF=

P= `ìêêÉåí=eáÖÜ=EHF=Q=

oÉ~Åíçê=o=sçäí~ÖÉ=içï=EJF=

R= `ìêêÉåí=eáÖÜ=EHF=S= `çäÇ=eçíïáêÉ=qÉãé= sçäí~ÖÉ=içï==EJF=

82

T= `ìêêÉåí=eáÖÜ=EHF=U=

`çäÇ=sçêíÉñ=qÉãé=sçäí~ÖÉ=içï=EJF=

V= `ìêêÉåí=eáÖÜ=EHF=NM=

oÉ~Åíçê=i=sçäí~ÖÉ=içï=EJF=

NN= `ìêêÉåí=eáÖÜ=EHF=NO=

eçí=sçêíÉñ=qÉãé=sçäí~ÖÉ=içï=EJF=

NP= `ìêêÉåí=eáÖÜ=EHF=NQ=

sçêíÉñ=fåäÉí=`ìêêÉåí=içï=EJF=

NR= sçäí~ÖÉ=eáÖÜ=EHF=NS=

oÉ~Åíçê=o=`ìêêÉåí=içï=EJF=

NT= sçäí~ÖÉ=eáÖÜ=EHF=NU=

`çäÇ=eçíïáêÉ=qÉãé=`ìêêÉåí=içï=EJF=

NV= sçäí~ÖÉ=eáÖÜ=EHF=OM=

`çäÇ=sçêíÉñ=qÉãé=`ìêêÉåí=içï=EJF=

ON= sçäí~ÖÉ=eáÖÜ=EHF=OO= oÉ~Åíçê=i= `ìêêÉåí=içï=EJF=OP= sçäí~ÖÉ=eáÖÜ=EHF=OQ=

eçí=sçêíÉñ=qÉãé=`ìêêÉåí=içï=EJF=

OR= sçäí~ÖÉ=eáÖÜ=EHF=

bäÉÅíêáÅ~ä=cÉÉÇíÜêçìÖÜ=OW=líÜÉê=ÉèìáéãÉåí=

máå= pÉåëçê= páÖå~ä=N= eçí=eçíïáêÉ=eÉ~íÉê= eáÖÜ=EHF=sçäí~ÖÉG=O= eÉ~íÉê=o= eáÖÜ=EHF=sçäí~ÖÉG=P= eÉ~íÉê=i= eáÖÜ=EHF=sçäí~ÖÉG=Q= `çåÇÉåëÉê=eÉ~íÉê= eáÖÜ=EHF=sçäí~ÖÉG=R= `çäÇ=eçíïáêÉ=pÉåëçê= eáÖÜ=EHF=sçäí~ÖÉG=S= eçí=eçíïáêÉ=qÉãé= =T= eçí=eçíïáêÉ=pÉåëçê= eáÖÜ=EHF=sçäí~ÖÉG=U= `çäÇ=eçíïáêÉ=eÉ~íÉê= eáÖÜ=EHF=sçäí~ÖÉG=V=

o~Çá~íáçå=pÜáÉäÇ=qÉãé=sçäí~ÖÉ=içï=EJF=

NM= `ìêêÉåí=eáÖÜ=EHF=NN=

`çåÇÉåëÉê=cä~åÖÉ=E`ÉêåçñF=sçäí~ÖÉ=içï=EJF=

NO= `ìêêÉåí=eáÖÜ=EHF=NP= eçí=eçíïáêÉ=qÉãé= =

83

NQ= eçí=eçíïáêÉ=eÉ~íÉê= içï=EJF=sçäí~ÖÉG=NR= eÉ~íÉê=o= içï=EJF=sçäí~ÖÉG=NS= eÉ~íÉê=i= içï=EJF=sçäí~ÖÉG=NT= `çåÇÉåëÉê=eÉ~íÉê= içï=EJF=sçäí~ÖÉG=NU= `çäÇ=eçíïáêÉ=pÉåëçê= içï=EJF=sçäí~ÖÉG=NV= eçí=eçíïáêÉ=qÉãé= =OM= eçí=eçíïáêÉ=pÉåëçê= içï=EJF=sçäí~ÖÉG=ON= `çäÇ=eçíïáêÉ=eÉ~íÉê= içï=EJF=sçäí~ÖÉG=OO=

o~Çá~íáçå=pÜáÉäÇ=qÉãé=sçäí~ÖÉ=eáÖÜ=EHF=

OP= `ìêêÉåí=içï=EJF=OQ=

`çåÇÉåëÉê=cä~åÖÉ=E`ÉêåçñF==sçäí~ÖÉ=eáÖÜ=EHF=

OR= `ìêêÉåí=içï=EJF=

GDirectionality does not matter in this case; our suggested directionality is given.===

=

pÉåëçê= máåë= kçãáå~ä=oÉëáëí~åÅÉ=EΩF=eçí=eçíïáêÉ=eÉ~íÉê= NI=NQ= úQV=

eÉ~íÉê=o= OI=NR= úOM=eÉ~íÉê=i= PI=NS= úOM=

`çåÇÉåëÉê=eÉ~íÉê= QI=NT= úNMM=`çäÇ=eçíïáêÉ=pÉåëçê= RI=NU= SKV=eçí=eçíïáêÉ=pÉåëçê= TI=OM= VKM=`çäÇ=eçíïáêÉ=eÉ~íÉê= UI=ON= úPU=

The wire leads in the cryostat are all labeled per what sensor/device they connect to. The labels

consist of one letter (T, H, C – Temperature, Heater, Composition) and one number (0-9) to

indicate what the wire bundle connects to.

i~ÄÉä= aÉîáÅÉ=qN= o~Çá~íáçå=pÉåëçê=qO= `Éêåçñ=pÉåëçê=qP= oÉ~Åíçê=o=qQ= eçíïáêÉI=eçí=páÇÉ=qR= oÉ~Åíçê=i=qS= sçêíÉñ=qìÄÉI=`çäÇ=páÇÉ=qT= sçêíÉñ=qìÄÉI=eçí=páÇÉ=qU= eçíïáêÉI=`çäÇ=páÇÉ=qV= sçêíÉñ=qìÄÉI=fåäÉí=

i~ÄÉä= aÉîáÅÉ=eN= eçíïáêÉI=eçí=páÇÉ=eO= eçíïáêÉI=`çäÇ=páÇÉ=eP= `çåÇÉåëÉê=q~åâë=eQ= oÉ~Åíçê=o=eR= oÉ~Åíçê=i=

i~ÄÉä= aÉîáÅÉ=`N= `çäÇ=páÇÉ=`O= eçí=páÇÉ=

GP-100 Platinum RTD wiring is shown below.

mçëáíáîÉ=iÉ~Ç=EdêÉÉåF=EoÉÇF=

kÉÖ~íáîÉ=iÉ~Ç=E_äìÉL_ä~ÅâF=EdçäÇL`äÉ~êF=

Cernox wiring is shown below.

mçëáíáîÉ=iÉ~Ç=EdêÉÉåF=EoÉÇF=

kÉÖ~íáîÉ=iÉ~Ç=E_äìÉL_ä~ÅâF=EdçäÇL`äÉ~êF=

=

XP-100 Platinum RTD wiring is shown below.

84

85

mçëáíáîÉ=iÉ~Ç=EdêÉÉåF=EoÉÇF=

kÉÖ~íáîÉ=iÉ~Ç= E_äìÉL_ä~ÅâF=EdçäÇL`äÉ~êF=

Lakeshore 336 temperature sensors must be wired into the Lake shore plugs designed to plug

into the back of the unit. The pinout for all temperature sensors is below:

Temperature sensors used with the Lakeshore 336 should either be supplied with a calibration

curve, or a Softcal should be performed..

The Lakeshore 336 has two heater circuits: Output 1 is 100W, Output 2 is 50W. Each of the

Reactor heaters is wired to a heater plug and plugged into the 100W heater for that Lakeshore

unit.

=

86

Each of the top and bottom Lakeshore 336 Temperature controllers has four temperature

channels, labeled A, B, C, D. Additionally, they have two heater outputs, as described in the

previous section. Input / output channel lists for each unit are in the sections below.

qÉãéÉê~íìêÉ=pÉåëçê=fåéìíë=`Ü~ååÉä= pÉåëçê= qóéÉ=

^= sçêíÉñ=fåäÉí= mä~íáåìã=oqa=Ó=O=éíK=pçÑíÅ~ä=_= sq=eçí= mä~íáåìã=oqa=Ó=OéíK=pçÑíÅ~ä=`= et=`çäÇ= mä~íáåìã=oqa=Ó=OéíK=pçÑíÅ~ä=a= oÉ~Åíçê=o= mä~íáåìã=oqa=Ó=OéíK=pçÑíÅ~ä=

eÉ~íÉê=lìíéìíë=`Ü~ååÉä= eÉ~íÉê= qóéÉ=lìíéìí=N= oÉ~Åíçê=o= `~êíêáÇÖÉ=eÉ~íÉê=lìíéìí=O= kçåÉ= kL^=

qÉãéÉê~íìêÉ=pÉåëçê=fåéìíë=`Ü~ååÉä= pÉåëçê= qóéÉ=

^= sq=`çäÇ= mä~íáåìã=oqa=Ó=O=éíK=pçÑíÅ~ä=_= oÉ~Åíçê=i= mä~íáåìã=oqa=Ó=OéíK=pçÑíÅ~ä=`= `çåÇÉåëÉê= `~äáÄê~íÉÇ=`Éêåçñ=a= jif=lo=eçíïáêÉI=eçí=páÇÉ= mä~íáåìã=oqa=Ó=OéíK=pçÑíÅ~ä=

eÉ~íÉê=lìíéìíë=`Ü~ååÉä= eÉ~íÉê= qóéÉ=lìíéìí=N= oÉ~Åíçê=i= `~êíêáÇÖÉ=eÉ~íÉê=lìíéìí=O= kçåÉ= kL^=

The Keller America pressure transducers have a three-wire setup with ground connection,

positive signal, and excitation voltage wires. The wiring is given in the chart below.

The pressure transducers on CHEF are cable conductor versions. These have been soldered to a

MIL connector to connect to the electrical plate on CHEF.

87

The hotwire heaters are custom made by wrapping Polyimide insulated nichrome wire around 18

AWG solid core copper wire. Two strands of the solid core wire are passed through a VCR

fitting to make a vacuum tight connection. One strand is cut to have a length of 5.4” pass the end

of the VCR fitting, and the other a length of 1.116” past the VCR fitting. The tip of the shorter

wire is stripped and the length of the longer wire past 1.116” is stripped. The nichrome wire is

then soldered to the tip of the shorter solid core wire and wrapped tightly around the stripped

length of the longer solid core wire. After wrapping approximately 1.5 meters of the nichrome

wire, the nichrome wire is soldered to the end of the longer solid core wire. The heater is then

coated in Stycast 2850 and wrapped in 0.005” copper foil. After curing, the copper foil is

trimmed, if necessary, and resistance checked. Resistance should be ~50Ω.

The nichrome used in the heaters is CryoCon’s single strand 32 AWG polyimide insulated

nichrome heater wire. This wire is an 80-20 alloy of nickel to chromium. The Polyimide

insulation is rated for operation up to 493K.

88

The front electrical panel on CHEF is wired for power and signal for the pressure transducers on

the left side, power, and signal for the hotwire measurement boards on the right side, and for the

emergency stop in the middle. This is the main control center for CHEF, and details on the

system are given in this section.

The left side of the board powers the pressure transducers and channels the signals from them

back to the DAQ board next to CHEF’s computer.

The right side of the board powers the hotwire measurement circuits, and receives a signal back

from the boards, which is then channeled back to the DAQ board.

The power cable is from H2scan, pinouts are given as in the manual for the HY-ALERTA Model

600:

táêÉ=`çäçê= aÉëÅêáéíáçå=_êçïå= HU=sa`=íç=HNP=sa`=tÜáíÉ= sa`=oÉíìêå=_ä~Åâ= mçëáíáîÉ=^å~äçÖ=lìíéìí=_äìÉ= ^å~äçÖ=lìíéìí=oÉíìêå=

The relay connector wire is a third-party wire from Amazon, and not the official H2scan cable.

Although the wire colors are similar to the H2scan cable pinout, the pinout is not the same. Do

not use the pinout in the manual. The correct pinout for our cable is given below.

táêÉ=`çäçê= aÉëÅêáéíáçå=dê~ó= oÉä~ó=N=`çããçå=máåâ= oÉä~ó=N=kçêã~ääó=`äçëÉÇ=Ek`F=vÉääçï= oÉä~ó=N=kçêã~ääó=léÉå=EklF=_êçïå= oÉä~ó=O=`çããçå=dêÉÉå= oÉä~ó=O=kçêã~ääó=`äçëÉÇ=Ek`F=tÜáíÉ= oÉä~ó=O=kçêã~ääó=léÉå=EklF=_äìÉ= råìëÉÇ=oÉÇ= råìëÉÇ=

89

The serial interface cable was delivered from H2scan, and the pinouts are as given in the manual.

The cable has been soldered to a DB9 connector with the correct pinout for either RS232 or

RS422 communications. The following pinouts match those found in the manual.

=

táêÉ=`çäçê= opOPO=aÉëÅêáéíáçå= opQOO=aÉëÅêáéíáçå= a_V=máå=_êçïå= HSs=EkK`KF= = =

tÜáíÉ= qña=EaÉîáÅÉ=qê~åëãáíF= qñaJ=EaÉîáÅÉ=qê~åëãáíI=kÉÖ~íáîÉF= P=

_äìÉ= J= qñaH=EaÉîáÅÉ=qê~åëãáíI=mçëáíáîÉF= Q=

_ä~Åâ= oña=EaÉîáÅÉ=oÉÅÉáîÉF= oñaJ=EaÉîáÅÉ=oÉÅÉáîÉI=kÉÖ~íáîÉF= O=

dê~ó= J= oñaH=EaÉîáÅÉ=oÉÅÉáîÉI=mçëáíáîÉF= S=

máåâ= dêçìåÇ= dêçìåÇ= R=

Mechanical / Fluid

The liquefaction tanks consist of two 4NPS schedule 10 pipes made of 6061 Aluminum.

These are sealed and supported by two custom machined 6061 Aluminum flanges. The bottom

flange has imbedded cartridge heaters to boil off the stored cryogen. The top flange has two

VCR adapters for gas flow out (1 for regular use, 1 for dedicated pressure relief) and a single

NPT port for hanging catalyst in the tank.

90

Tank assembly drawing Tank bottom flange design Tank top flange design

The specifications for the materials used in tank construction are given below:

níóK= j~íÉêá~ä= qK= tLa= iK= e~êÇåÉëë= qÉãéÉê= péÉÅK= mLk=O= SMSN=^ä= MKNOÒ= QKRÒ= NÛ= J= J= ^pqj=_OQN= QRSNqVNN=

N=E½=H=½F== SMSN=^ä= ½Ò= SÒ= PÛ= _êáåÉää=VR= qSRNN= ^pqj=_OON= VQQPR^PPU=

The flanges are secured together to seal the tanks with 28 individual threaded rods. These rods

are also what secure the tanks to the cold head.

Of the 28 threaded rods, 26 are No. 8 and two are ¼”. The central two No.8 rods thread into the

bottom flange, and the two ¼” rods thread into the second stage of the cold head. These two ¼”

rods are the only means of securing the tank to the cold head.

qÜêÉ~ÇÉÇ=oçÇ=péÉÅáÑáÅ~íáçåë=níóK= qÜêÉ~Ç=páòÉ= j~íÉêá~ä= jáå=qÉåëáäÉ=

píêÉåÖíÜ=jáå=e~êÇåÉëë= qÜêÉ~Ç=cáí= mLk=

OS= U=J=PO= SMSN=^ä= QMIMMM=éëá= oçÅâïÉää=_QM= N^= VQQPR^PNV=O= ¼=J=OM= SMSN=^ä= QMIMMM=éëá= oçÅâïÉää=_QM= N^= VQQPR^PPU=

91

=aê~ïáåÖ=áåÇáÅ~íáåÖ=íÜÉ=äçÅ~íáçåë=çÑ=É~ÅÜ=íÜêÉ~ÇÉÇ=êçÇ=çå=íÜÉ=í~åâ=Ñä~åÖÉë=

Stainless steel fat washers have been selected to tighten the tank seal at cryogenic temperatures.

The stainless-steel washers will contract less than the aluminum threaded rod (which contracts at

nearly identical rate to the tanks due to the matched materials). The specifications are given

below.

níóK= páòÉ= fa= la= qÜáÅâåÉëë= j~íÉêá~ä= jáå=e~êÇåÉëë= mLk=RM= kçK=U== MKNTOÒ= MKRMMÒ= MKMRMÒJ

MKMUMÒ=PNS=pp= oçÅâïÉää=_SU= VNROR^PNU=

O= ¼Ò= MKOSSÒ= MKRMMÒ= MKNNMÒJMKNQMÒ=

PNS=pp= oçÅâïÉää=_SU= VNROR^POQ=

A thermal contraction analysis of this system shows that the addition of the steel thickness in the

washers will contribute an additional tensioning of the threaded rod by 0.0001675 inches.

Two tapped holes that extend only partially into the bottom flange are machined to allow a brass

screw with spring secure a Cernox temperature sensor to the bottom of each liquefier tank. These

tapped holes are located away from both the tank heaters and the attachment location for the

second stage of the cryocooler coldhead to reduce any error that might be induced by

temperature gradients near these heat sources and sink.

92

Two tank cartridge heaters are embedded in the bottom flange of the liquefier tank, one directly

below the center of each tank. These have been epoxied into a slot cut into the flange of the tank

with Loctite EA 9361 AERO cryogenic rated epoxy. Wiring for these is discussed in Section 2.

q~åâ=eÉ~íÉê=péÉÅáÑáÅ~íáçåë=níóK= aá~K= iÉåÖíÜ= mçïÉê= `ìêêÉåí= sçäí~ÖÉ= j~ñ=qÉãéK= mLk=O= MKOQTÒ= NÒ= UM=t= MKT=^= 120V AC 1400°F 3614K34

The coldhead being used is a Sumitomo Heavy Industries (SHI Cryogenics of America)

CH204SFF – N in its inverted position. Specifications on the coldhead are listed below:

Part Number: 267104D – N

Serial Number: CH1012

Date of Manufacture: 05/2011

The helium compressor being used in CHEF is a SHI Cryogenics HC-4E1. Specifics are detailed

below:

Part Number: 266958D1618G

Serial Number: SP0423

Date of Manufacture: 08/2011

To verify that the relief device(s) sizing was adequate we consulted a print copy of the CGA S-

1.3 standard. This code contained “commodity-based requirements” in section 4.3 which

included “Liquefied compressed gases, refrigerated fluids and refrigerated (cryogenic) fluids” in

4.3.3. throughout the following calculations we assumed a worst case scenario in which the

inside vacuum area of CHEF is at atmospheric pressure and hydrogen gas has filled the internal

vacuum volume. Fire is not a concern for this design. Therefore, the parameters in which the

valve(s) flow rate in the primary stage are specified in 4.3.3.1:

93

“The minimum total flow capacity of the primary system of pressure relief valves for operational

emergency conditions, except fire, shall be calculated using the applicable formula in 5.2.2 for a

flow rating pressure not to exceed 110 percent and 116 percent of the MAWP of the container,

respectively, for single and multiple primary pressure relief valves.”

Therefore, the formula in 5.2.2 was used to determine:

"5.2.2 - The total minimum required flow capacity for the pressure control valve(s) or primary

pressure relief device(s) on insulated containers for liquefied compresses gases, refrigerated

fluids, and refrigerated (cryogenic) fluids shall be calculated by the formula:"

Q= =>./@/∗(B0CDE.F.G)

(B,CDE.F.G)∗ F ∗ GJ ∗ U ∗ A

Where F = Correction factor specified in 5.1.4:

F5.1.4 = MNO_JE.F.Q∗D_JE.F.QOE.F.G∗DE.F.GR = 7.814

This correction factor accounts for the maximum compressibility differences at the venting

conditions assuming worst case scenario (the hydrogen has warmed up to the external container

conditions (293K and atmospheric pressure) to the condition for this same flow rating pressure of

145psi, but where the ratio of the specific volume to the specific heat input (at a constant

pressure) multiplied by the specific volume. This occurs at 33.5K and 145psi flow rating

pressure which results in a Z5.1.3 of 0.2706 compared to the compared to that of the room

temperature hydrogen which Z5.1.4 = 1.0075.

Please refer to appendix A or the CGA S-1.3 for a complete description of the constituent

variables in section 5.1.4.

GI = The Gas Factor constant for hydrogen as calculated through the example problem in the

code on pages 26 – 31. The example followed mirrors the metric unit example on the bottom of

94

page 30. This value equates to U = Overall Heat Transfer coefficient in kJ/(hr*m2 *C) assuming

worst case scenario with no vacuum, hydrogen gas filled insulation space at room temperature.

This is a very extreme case which in assumes steady state from the beginning of a power outage.

As we saw in out anomaly with CHEF, the vacuum slowly decreased and the temperature of the

metal components within the experiment also take a significant amount of time to warm. The

estimated steady state overall heat transfer within CHEF during the anomaly to be 3.701 W/m2K.

While a sudden loss of vacuum is also possible we estimated through a flat plate EES estimate of

an atmospheric pressure, hydrogen gas laden on the 22K liquefier exterior area. This estimate

provided a heat transfer over 4-times higher at 16.31 W/m2K.

A = Area of the outside of CHEF’s liquefier: 0.2782 m2

The result of these calculations was a required flow capacity of 19.73 cubic feet per minute (cfm)

of air at 60 degrees F between all primary pressure relief valves.

In our system we have 3 primary relief valves to account for the liquefier shutoff valve to the

liquefier. One attached to the reservoir vapor space and the other two in communication with the

liquefier vapor space. See the P&ID diagram below:

95

The secondary stage of CHEF’s pressure reliefs are aimed to act as an additional safety

redundancy. The burst (rupture) disks are used in combination with the pressure relief valves to

to provide a last resort if the pressure in CHEF increases to 200 psi. This is near impossible and

unlikely as the primary stage has three pressure reliefs which have a real factor of safety of 20

over a chocked flow analysis. The burst disk is manufactured by BS&B and has extensive

material information included. See the details below for specific calculations.

Software, Data Collection, and Control

Platinum RTDs are calibrated using a LakeShore Cryotronics 2-point Softcal (one control

point at ~77 K and one control point at ~305 K) Control points are listed below. The first set

point was measured in liquid nitrogen, recording resistances measured by the LakeShore 336 and

room pressure measured by the Paroscientific 740-16B. This room pressure was correlated to a

liquid nitrogen temperature using REFPROP. The second point was measured at lab room

96

temperature, recording resistances from the LakeShore 336 and temperature of the room on a

Comark PDT300 or factory-calibrated Cernox sensor.

pÉêá~ä=@= içÅ~íáçå= oÉëáëí~åÅÉ=N= mêÉëëìêÉ=N= qÉãé=N= oÉëáëí~åÅÉ=O= qÉãé=O=

TMMN= sq=`çäÇ= OOKOSOQ=xΩ]= NPKPUST=xéëáz= TSKRTO=xhz= NMVKOST=xΩz= OVRKUOR=xhz=

TMMO= sçêíÉñ=fåäÉíG= OMKMUTO=xΩz= NPKPURR=xéëáz= TSKRTO=xhz= NMUKVMV=xΩz= OVRKUTO=xhz=

TMMP= oÉ~Åíçê=i= OMKMVP=xΩz= NPKPURR=xéëáz= TSKRTO=xhz= NMUKVVO=xΩz= OVQKQPU=xhz=

TMMQ= o~Ç= NVKQOM=xΩz= NPKQOUU=xéëáz= TSKRVU=xhz= NMUKTMM=xΩz= OVRKQUN=xhz=

TMMR= bñíê~=oÉ~Åíçê= = = = = =

TMMS= oÉ~Åíçê=o= OMKVTUN=xΩz= NPKPUTQ=xéëáz= TSKRTP=xhz= NMVKNMS=xΩz= OVSKUTN=xhz=

TMMT= et=eçí= OMKPNM=xΩz= NPKRMQS=xéëáz= TSKSQR=xhz= NMVKNRM=xΩz= OVSKOMS=xhz=

TMMU= sq=eçí= OMKPTTM=xΩz= NPKPUTS=xéëáz= TSKRTP=xhz= NMUKUUP=xΩz= OVSKUSN=xhz=

TMMV= et=`çäÇ= OMKMTM=xΩz= NPKRMRQ=xéëáz= TSKSQR=xhz= NMUKUVR=xΩz= OVRKVUP=xhz=

The condenser tank temperature is given by a Cernox sensor mounted to the lower flange of the

tanks. Calibration data below.

Serial number: X63718

fåÇÉñ= qÉãé=xhz= oÉëáëí~åÅÉ= bñÅáí~íáçå= fåÇÉñ= qÉãé=xhz= oÉëáëí~åÅÉ= bñÅáí~íáçå=N= NKNVVTS= RNRKUTU= Oãs±ORB= QP= PPKMQPP= VTKMSSV= Oãs±ORB=O= NKPMMRO= QUQKQSP= Oãs±ORB= QQ= PSKMQSU= VPKQTVS= Oãs±ORB=P= NKPVVQQ= QRUKQNU= Oãs±ORB= QR= PVKMPTU= VMKOTPR= Oãs±ORB=Q= NKSMMPQ= QNRKVRP= Oãs±ORB= QS= QOKMPTP= UTKPSNM= Oãs±ORB=R= NKUMMTT= PUPKQQS= Oãs±ORB= QT= QRKMPSR= UQKTMOO= Oãs±ORB=S= OKMMMTP= PRTKSTO= Oãs±ORB= QU= QUKMPMT= UOKOTPO= Oãs±ORB=T= OKOMMVT= PPSKRNU= Oãs±ORB= QV= RMKMONM= UMKTSNP= Oãs±ORB=U= OKQMNPP= PNUKUUR= Oãs±ORB= RM= RRKMOOS= TTKOVRT= Oãs±ORB=V= OKRVVUM= PMQKMNR= Oãs±ORB= RN= SMKMOOO= TQKOOVU= Oãs±ORB=NM= OKTVVMP= OVNKNTS= Oãs±ORB= RO= SRKMNUQ= TNKQVMM= Oãs±ORB=NN= PKMMMRS= OTVKUOS= Oãs±ORB= RP= TMKMNPT= SVKMOOM= Oãs±ORB=NO= PKNVVSR= OSVKVUT= Oãs±ORB= RQ= TRKMNMQ= SSKTTVT= Oãs±ORB=NP= PKQMMVR= OSNKNPP= Oãs±ORB= RR= UMKMMOP= SQKTPMT= Oãs±ORB=NQ= PKSMMMQ= ORPKOVT= Oãs±ORB= RS= UQKVVUV= SOKUQSQ= Oãs±ORB=

97

NR= PKUMMTN= OQSKNTO= Oãs±ORB= RT= UVKVVRR= SNKNMMT= Oãs±ORB=NS= PKVVVOV= OPVKTPQ= Oãs±ORB= RU= VQKVVNU= RVKQUOO= Oãs±ORB=NT= QKOMPVU= OPPKTMR= Oãs±ORB= RV= VVKVVPR= RTKVTNT= Oãs±ORB=NU= QKSQQQV= OOOKPUN= Oãs±ORB= SM= NMVKVUU= RRKOOVV= Oãs±ORB=NV= RKMQRVQ= ONPKRUO= Oãs±ORB= SN= NNVKVVN= ROKUMPT= Oãs±ORB=OM= RKRROVP= OMQKMUQ= Oãs±ORB= SO= NOVKVUR= RMKSPMQ= Oãs±ORB=ON= SKORTOV= NVPKNSP= Oãs±ORB= SP= NPVKVUP= QUKSTOO= Oãs±ORB=OO= TKMSUTP= NUOKUUN= Oãs±ORB= SQ= NQVKVUN= QSKUVQV= Oãs±ORB=OP= UKMUQSO= NTOKQVQ= Oãs±ORB= SR= NRVKVUS= QRKOTNU= Oãs±ORB=OQ= VKMVVNT= NSQKMST= Oãs±ORB= SS= NSVKVUV= QPKTURO= Oãs±ORB=OR= NMKNNSR= NRSKVVM= Oãs±ORB= ST= NTVKVUS= QOKQNRV= Oãs±ORB=OS= NNKNPSU= NRMKVOV= Oãs±ORB= SU= NUVKVTT= QNKNRPT= Oãs±ORB=OT= NOKNRMO= NQRKTMS= Oãs±ORB= SV= NVVKVUR= PVKVUNU= Oãs±ORB=OU= NPKNRUV= NQNKNMM= Oãs±ORB= TM= OMVKVVN= PUKUVQV= Oãs±ORB=OV= NQKNRVU= NPTKMQQ= Oãs±ORB= TN= ONVKVUR= PTKUURO= Oãs±ORB=PM= NRKNQUM= NPPKQPN= Oãs±ORB= TO= OOVKVUM= PSKVQPS= Oãs±ORB=PN= NSKNPQQ= NPMKNNT= Oãs±ORB= TP= OPVKVUU= PSKMSPQ= Oãs±ORB=PO= NTKNNPM= NOTKNMM= Oãs±ORB= TQ= OQVKVUQ= PRKOPVO= Oãs±ORB=PP= NUKMVPQ= NOQKPOM= Oãs±ORB= TR= ORVKVUQ= PQKQSSM= Oãs±ORB=PQ= NVKMSUN= NONKTQO= Oãs±ORB= TS= OSVKVUT= PPKTQOQ= Oãs±ORB=PR= OMKMQUP= NNVKPOT= Oãs±ORB= TT= OTVKVUS= PPKMRTM= Oãs±ORB=PS= ONKNPNT= NNSKUOV= Oãs±ORB= TU= OVMKMMM= POKQNRV= Oãs±ORB=PT= OOKTNOR= NNPKQTP= Oãs±ORB= TV= PMMKMMO= PNKUNNM= Oãs±ORB=PU= OQKPMSM= NNMKPUU= Oãs±ORB= UM= PNMKMMU= PNKOPVQ= Oãs±ORB=PV= ORKUUTU= NMTKRST= Oãs±ORB= UN= PNRKMNQ= PMKVSRT= Oãs±ORB=QM= OTKQVVU= NMQKVMS= Oãs±ORB= UO= POMKMNR= PMKSVTR= Oãs±ORB=QN= OVKNNRM= NMOKQPR= Oãs±ORB= UP= POSKMMU= PMKPUUM= Oãs±ORB=QO= PMKVPQO= VVKUQPM== Oãs±ORB= UQ= PPMKMNQ= PMKNUST= Oãs±ORB=