Refrigerants - WordPress.com

Refrigerants

Prof. R. C. Patil Mechanical Engg

History Of Refrigeration• Most evidence indicate that the Chinese were the first to store

natural ice and snow to cool wine and other delicacies.

• Ancient people of India and Egypt cooled liquids in porous earthenjars.

• In 1834, Jacob Perkins, an American, developed a closedrefrigeration system using liquid expansion and then compression toproduce cooling.He used Ether as refrigerant, in a hand- operated compressor, awater-cooled condenser and an evaporator in liquid cooler.

❑1850’s – 1870’s: ammonia, ammonia/water, CO2

❑Early 1900’s: SO2, methyl chloride used for domestic refrigerators

❑1930’s: halocarbon refrigerants (R-12, R-22, R-114, R-22)Halocarbon advantages – stable compounds, favorable thermodynamicproperties, safer than existing refrigerants.

2Prof.R.C. Patil Mechanical Department

Refrigeration Principle

• Modern refrigeration and air-conditioning

equipment is dominated by vapour compression

refrigeration technology built upon the

thermodynamic principles of the reverse Carnot

cycle.

• Refrigerant Changes phase during cooling

and used again and again.


Importance of Refrigerant

• The thermodynamic efficiency of a refrigerationsystem depends mainly on its operating temperatures.

• However, important practical issues such as thesystem design, size, initial and operating costs,safety, reliability, and serviceability etc. depend verymuch on the type of refrigerant selected for a givenapplication.

• Due to several environmental issues such as ozonelayer depletion and global warming and their relationto the various refrigerants used, the selection ofsuitable refrigerant has become one of the mostimportant issues in recent times.


What is a Refrigerant• Working substances

• Primary and Secondary refrigerants.

• Primary refrigerants are those fluids, which are used directlyas working fluids.

Ex.-refrigerant used in VCC and VAR systems.These fluids provide refrigeration by undergoing a phasechange process in the evaporator.

• Secondary refrigerants are those liquids, which are used fortransporting thermal energy from one location to other.

•Secondary refrigerants are also known under the namebrines or antifreezes.


• The refrigerants which are directly used toobtain the cooling effect in evaporator byundergoing a phase change process are referredas Primary refrigerants.

• Halocarbon Refrigerants

• Azeotropes Refrigerants

• Inorganic Refrigerants

• Hydro-carbon Refrigerants

Primary Refrigerant


• Used for transporting thermal energy from onelocation to other.

• Does not undergo phase change process.

• Used when refrigeration is required at sub-zerotemperatures.

• Known as Brines or Antifreezes.

• Used in large refrigeration units.

• Commonly used secondary refrigerants are:-

Solution of water & ethylene glycol, propyleneglycol etc.

Secondary Refrigerant


• If working temperature is above 30C, Water is used as SR.

• Brine is aqueous solution of NaCl and CaCl2 in water and usedat temperature below freezing point of water 00C.

Used in cooling of fish, meat & ice plant.

• Ethylene glycol & Propylene glycol mixes with water and givescolorless & odourless solutions.

These have capacity to lower freezing temperatures andhence used as antifreeze mixtures for I.C. engine coolingsystems.

These solutions become corrosive after some use, hencecorrosive treatment is necessary.

Secondary Refrigerant


• Different rooms of building can be cooled up todifferent temperatures by adjusting the flowrates of secondary refrigerants.

• SR can be easily handled.

• SR can be easily controlled.

• Eliminates long refrigeration lines and thusreduces pressure drops.

Advantages of Secondary Refrigerant


• Low freezing point.

• High heat transfer coefficients.

• High specific heat.

• Low vapour pressure.

• Good stability.

• Non-flammable and non-toxic.

Desirable Properties of Secondary Refrigerant


• CFC –Chlorofluorocarbons (Freon‘s)

• HCFC -Hydrochlorofluorocarbon

• HFC -Hydrofluorocarbon

Primary Refrigerant


• CFC’s ❖ First developed by General Motor’s researchers in the 1920’s

and commercialized as Freon‘s.❖ Most stable – remain in atmosphere for many years, allowing them

to diffuse to high altitudes❖ Contains Chlorine, Fluorine, Carbon.❖ CFC’s break down, and Cl combines with and consumes some ozone

• HCFC’s❖ Hydrogenated❖ Not as stable – most of it breaks down before reaching high

altitudes❖ Contains Hydrogen, Chlorine, Fluorine, Carbon.❖ Less damaging to ozone

• HFC’s❖ Contains Hydrogen, Fluorine, Carbon.

❖ Contains no Cl (Chlorine)

❖ Causes no depletion of ozone

Primary Refrigerant


Halocarbon Refrigerants

• Synthetically produced (Derived from Methane , Ethane) and weredeveloped as the Freon family of refrigerants.

• Commonly used in Domestic, Commercial and Industrial Purposes due totheir wide range of boiling points at atmospheric pressure.

• Presence of fluorine makes it Non-toxic.

• Ozone unfriendly refrigerants.


Halocarbon Refrigerants

Examples :– CFC’s (CHLOROFLUROCARBONS):

R11 (CCl3F) TrichloromonofluromethaneR12 (CCl2F2) DichlorodifluoromethaneR40 (CH3Cl) Methyl ChlorideR13, R21, R22,R113, R114, R115

- HCFC’s(HYDROCHLOROFLUROCARBONS):R22 (CHClF)2 Monochlorodifluromethane

R123 (C2HCl2F3) Dichlorotrifluoroethane

- HFC’s (HYDROFLUROCARBONS):- R134a (CH2FCF3)Tetrafluoroethane- R404a, R407C,- R410a mixture of Difluromethane (CH2F2, called R-32) and

Pentafluroethane (CHF2CF3, called R-125)


• A stable mixture of two or several refrigerants whosevapour and liquid phases retain identical compositions over awide range of temperatures.

• Thermodynamic properties remains fixed.

• Code starts with digit 5.

Examples

R500 – mixture of 73.8% of R12 and 26.2% of R152

R502 – Mixture of 49% of R22 and 51% of R115

Azeotrope (Mixed) Refrigerants


Zeotropic Refrigerants

• A zeotropic mixture is one whose composition in liquid phasediffers to that in vapour phase.

• Zeotropic refrigerants therefore do not boil at constanttemperatures unlike azeotropic refrigerants.

Examples :R404a : R125/143a/134a (44%,52%,4%)R407c : R32/125/134a (23%, 25%, 52%)R410a : R32/125 (50%, 50%)R413a : R600a/218/134a (3%, 9%, 88%)


• Before Halocarbons, Natural refrigerants are extensivelyused.

• Designated by R followed by Number.

Number = 700 + M

Example

Carbon Dioxide , Water , Ammonia , Air , Sulphur dioxide

R717 - (NH3)Ammonia

717 = 700 + 17

Inorganic (Natural) Refrigerants


• Satisfactory Thermodynamic properties.

• Extraordinary reliability- The most convincing argument is the reliability ofthe hydrocarbon system because of fewer compressor failures.

• .

• Virtually no refrigerant losses.

• Hydrocarbons have been used since the beginning of the century and nowbeing considered as long term solutions to environmental problems.

• But most of the hydrocarbons are highly flammable and require additionalsafety precaution during its use as refrigerants

• Not used in Industry and commercial installations.

• Dominant in domestic market like household refrigerators and freezers

• Growing use in very small commercial systems like car air-conditioning system.

Examples:

R170 – Ethane (C2H6)

R600 – Butane (C4H10)

R600a – Isobutane (C4H10)

Hydro-carbon Refrigerants


Current/Future Refrigerants

• R-134a has emerged as the primary substitution formany CFC’s.

• HCFC-22 and HCFC–123 are viable alternatives fornow but will eventually be phased out.

• In Europe, natural refrigerants such as ammonia,CO2, propane, and water are being used more.

• Our legal system makes flammable refrigerantsquestionable in the US.


Environmental Effects of Refrigerants

Global warming :

Refrigerants directly contributing to global warming whenreleased to the atmosphere.

Indirect contribution based on the energy consumption ofamong others the compressors ( CO2 produced by powerstations ).

Ozone Depletion:NOTE THAT GLOBAL WARMING AND OZONE DEPLETION ARE DIFFERENT PROBLEMS WITH DIFFERENT CAUSES. (A lot of people mess up on this on exams.)


What is Ozone Layer• Ozone (O3) is an isotope of oxygen with three atoms instead of

normal two.

• It is naturally occurring gas which is created by high energyradiation from the Sun.

• The greatest concentration of ozone are found from 12 km to 50km above the earth forming a layer in the stratosphere which iscalled the ozone layer.

• This layer, which forms a semi-permeable blanket, protects theearth by reducing the intensity of harmful ultra-violet (UV)radiation from the sun.


Ozone Layer Depletion

• In the early70’s,scientists Sherwood Roland andMario Molina at the University of California atIrvine were the first to discover the loss of ozonein stratosphere while investigating the ozone layerfrom highflying aircraft and spacecraft.

• They postulated the theory that exceptionallystable chlorine containing fluorocarbons could,overtime, migrate to the upper reaches of theatmosphere and be broken by the intenseradiation and release chlorine atoms responsiblefor catalytic ozone depletion.


OZONE LAYER DEPLETION

N0RMAL REACTION

O2 = O + OO2 + O = O3

• But CFC refrigerants leaked during the manufacturing and normaloperation or at the time of servicing or repair, mix withsurrounding air and rise to troposphere and then into stratospheredue to normal wind or storm.

• The Ultraviolet rays act on CFC releasing Cl atom, which retards thenormal reaction:

RETARDED REACTION

O3 = O2 + OCCL2F2 = CCLF2 + CLO3 + CL = CLO + O2


Harmful consequences of ozone depletion

• For Humans – Increase in skin cancer– slow blindness– Cataracts

• Less immunity to– infectious diseases - malaria -herpes

• For plants– smaller size -lower yield -increased toxicity– altered form

• For marine life– Reduced plankton -juvenile fish– larval crabs and shrimps 24Prof.R.C. Patil

Mechanical Department

Refrigerant selection criteria

• Selection of refrigerant for a particular applicationis based on the following requirements:

– Thermodynamic and thermo-physical properties

– Environmental and safety properties

– Economics


Thermodynamic and thermo-physical properties

The requirements are: a) Suction pressure:

At a given evaporator temperature, the saturation pressure should beabove atmospheric for prevention of air or moisture ingress into thesystem and ease of leak detection.

Higher suction pressure is better as it leads to smaller compressordisplacement.

b) Discharge pressure: At a given condenser temperature, the discharge pressure should be assmall as possible to allow light-weight construction of compressor,condenser etc.

c) Pressure ratio: Should be as small as possible for high volumetric efficiency and lowpower consumption.



d) Latent heat of vaporization: Should be as large as possible so that the required mass flow rate perunit cooling capacity will be small.

In addition to the above properties; the following properties arealso important:

e) Isentropic index of compression:Should be as small as possible so that the temperature rise duringcompression will be small.

f) Liquid specific heat:Should be small so that degree of sub cooling will be large leading to

smaller amount of flash gas at evaporator inlet.

g) Vapour specific heat:Should be large so that the degree of superheating will be

small.


h) Thermal conductivity:

Thermal conductivity in both liquid as well as vapour phase should behigh for higher heat transfer coefficients .

i) Viscosity:

Viscosity should be small in both liquid and vapour phases for smallerfrictional pressure drops.

• The thermodynamic properties are interrelated andmainly depend on normal boiling point, criticaltemperature, molecular weight and structure.



Environmental and safety properties

• At present the environment friendliness of the refrigerant isa major factor in deciding the usefulness of a particularrefrigerant.

• The important environmental and safety properties are:

• a) Ozone Depletion Potential (ODP):According to the Montreal protocol, the ODP of refrigerants should bezero, i.e., they should be non-ozone depleting substances.

Refrigerants having non-zero ODP have either already been phased-out(e.g. R 11, R 12) or will be phased-out in near-future(e.g. R22).

Since ODP depends mainly on the presence of chlorine or bromine inthe molecules, refrigerants having either chlorine (i.e., CFCs andHCFCs) or bromine cannot be used under the new regulations.



b) Global Warming Potential (GWP):Refrigerants should have as low a GWP value as possible to minimize theproblem of global warming.

Refrigerants with zero ODP but a high value of GWP (e.g. R134a) arelikely to be regulated in future.

c) Total Equivalent Warming Index (TEWI):The factor TEWI considers both direct (due to release into atmosphere)and indirect (through energy consumption) contributions of refrigerantsto global warming.

Naturally, refrigerants with as a low a value of TEWI are preferablefrom global warming point of view.


d) Toxicity:Ideally, refrigerants should be non-toxic.

Toxicity is a relative term, which becomes meaningful only when thedegree of concentration and time of exposure required to produceharmful effects are specified.

In general the degree of hazard depends on:

- Amount of refrigerant used vs total space

- Type of occupancy

- Presence of open flames

- Odor of refrigerant, and

– - Maintenance condition



e) Flammability:The refrigerants should preferably be non-flammable and non-explosive.

For flammable refrigerants special precautions should be taken to avoidaccidents.

f) Chemical stability:The refrigerants should be chemically stable as long as they are insidethe refrigeration system.

g) Compatibility with common materials of construction (both metalsand non-metals)



h) Miscibility with lubricating oils:

Oil separators have to be used if the refrigerant is not miscible withlubricating oil (e.g. ammonia).

Refrigerants that are completely miscible with oils are easier tohandle(R12).

i) Ease of leak detection:

In the event of leakage of refrigerant from the system, itshould be easy to detect the leaks.



• The refrigerant used should preferably beinexpensive and easily available.

Economic Properties


ECO-FRIENDLY REFRIGERANTS

HCFC

R22,R124

HFC

R134a,R152a

NATURAL REFRIGERANT

NH3, HC'S

CFC

ALTERNATIVES.


Application of New Eco-friendly Refrigerants

• Application HFCs used Possible Eco-friendly refrigerant

•

• Domestic refrigeration R134a,R152a HC600a and blends

• Commercial refrigeration R134a,R404A,R407C HC blends,NH3 ,CO2 **

• Cold storage ,food processing

• And industrial refrigeration R134a,R404A,R507A NH3 ,HCs,CO2 **

• Unitary air conditioners R410A,R407C CO2 , HC s

• Centralized AC (chillers) R134a,R410A,R407C NH3 ,HCs,CO2, water **

• Transport refrigeration R134a,R404A CO 2,

• Mobile air conditioner R134a CO2 ,HCs

• Heat pumps R134a,R152a,R404A NH3 ,HCs,CO2, water **

• R407C,R410A


R22

• ODP-0.05, GWP-1700

• R22 has 40% more refrigerating capacity

• Higher pressure and discharge temp and notsuitable for low temp application

• Extensively used in commercial air-conditioningand frozen food storage and display cases


R123

• ODP-0.02,GWP-90

• As a replacement for R11 as similarthermodynamic properties.

• Very short atmospheric life

• Retrofit alternative to R11


R134a

• ODP-0, GWP-1300

• Used as a substitute for R12 and to a limited range for R22

• Good performance in medium and high temp application

• Toxicity is very low

• Not miscible with mineral oil


R152a

• ODP-0,GWP-140

• R152a is another attractive HFC with similarproperties to R12.

• GWP is one order less than HFC134a but it isslightly flammable.

• Also it has lower energy consumption. Hence theEnvironmental Protection Agency of Europeprefers HFC152a to HFC134a


R290

• ODP-0,GWP-3

• Compatible with copper.

• Miscible with mineral oil

• Highest latent heat and largest vapour density

• A third of original charge only is required whenreplacing halocarbons refrigerant in existingequipment

• Energy saving : up to 20% due to lower molecularmass and vapour pressure


R 600a

• ODP-0,GWP-3

• Higher boiling point hence lower evaporatorpressure

• Discharge temp is lowest

• Very good compatibility with mineral oil


Carbon Dioxide• Zero ODP & GWP

• Non Flammable, Non toxic

• Inexpensive and widely available

• Its high operating pressure provides potential for systemsize and weight reducing potential.

Drawbacks:• Operating pressure (high side) : 80 bars

• Low efficiency


Ammonia – A Natural RefrigerantAmmonia is produced in a natural way by humanbeings and animals; 17 grams/day for humans.

Natural production 3000 million tons/year

Production in factories 120 million tons/year

Used in refrigeration 6 million tons/year

Ammonia as Refrigerant


Ammonia as Refrigerant

• ODP = 0 and GWP = 0

• Excellent thermodynamic characteristics: small molecular mass, large latent heat, large vapour density and excellent heat transfer characteristics

• High critical temperature (132C) : highly efficient cycles at high condensing temperatures

• Its smell causes leaks to be detected and fixed before reaching dangerous concentration

• Relatively Low price


Some Drawbacks of Ammonia as Refrigerant

• Toxic

• Flammable ( 16 – 28% concentration )

• Not compatible with copper

• Temperature on discharge side of compressor is higher compared to other refrigerants


Water• Zero ODP & GWP

• Water as refrigerant is used in absorption system .New developing technology has created space for it for use in compression cycles also.

• But higher than normal working pressure in the system can be a factor in restricted use of water as refrigerant


Freon Group Refrigerants Application and ODP

Values

Refrigerant Areas of Application ODP

CFC 11(R11)

CFC 12 ( R 12 )

CFC 13 (R 13)

CFC113 (R113 )

CFC114 (R114 )Blend of R22and R115(R502)

Air-conditioning Systems ranging from 200 to2000 tons in capacity. It is used where lowfreezing point and non-corrosive properties areimportant.It is used for most of the applications. Air-conditioning plants, refrigerators, freezers, ice-cream cabinets, water coolers, window air-conditioners, automobile air conditioners.For low temp refrigeration up to – 90 C incascade system

Small to medium air-conditioning system andindustrial cooling

In household refrigerators and in large industrialcoolingFrozen food ice-cream display cases andwarehouses and food freezing plants. Anexcellent general low temp refrigerant

1.0

1.0

1.0

1.07

0.80.34


General Safety measures for refrigerating plants

• Reduction of refrigerant contents:– Components with reduced contents– Indirect systems with secondary refrigerant: distinction

between generation and transport of cold

• Scheduled maintenance and leak testing

• Governmental surveillance – Refrigerant Audits for systems operating with HFC’s. Recovery, Stock of used refrigerants, Recycling of refrigerants.

• For the Netherlands, the combined measures resulted in a leak rate reduction of 35% (1995) to 8% (2001) for R22-systems


MONTREAL PROTOCOL

• SIGNED IN 1987 UNDER THE ‘UNEP’(United nationsenvironment programme ), AFTER MUCH DISCUSSIONS

• MORE THAN 170 COUNTRIES HAVE RATIFIED

• INDIA RATIFIED ON SEPT 17,1992

• ONE OF MOST SUCCESSFUL EXAMPLE OFINTERNATIONAL COOPERATION IN UN HISTORY


Montreal protocol- Control Schedule

Ozone depleting

substance

Developed countries Developing countries

CFCs phased out end of

1995

total phase out by

2010

halons phased out end of

1993

total phase out by

2010

HCFCs total phase out by

2020

total phase out by

2040


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