EXPERIMENT ANALYSIS AND PERFORMANCE TESTING OF CAPILLARY TUBE AND THERMOSTATIC EXPANSION VALVE

EXPERIMENTANALYSISANDPERFORMANCETESTINGOFCAPILLARYTUBEANDTHERMOSTATICEXPANSIONVALVE

1AMOLA.GAWALI,2MADHAVS.JOSHI,3RUPESHL.RAUT,4RAHULA.BHOGARE

1,3,4Student,HeatPowerEngineering,WalchandCollegeofEngineering,Sangli,Maharashtra,INDIA

2AssociateProfessor,MechanicalEngineering,WalchandCollegeofEngineering,Sangli,Maharashtra,INDIA

Email:[email protected],[email protected],[email protected],[email protected]

ABSTRACT

Thispaperprovideanoverviewoftheproject,thefundamentalphysicsunderlyingthe

operation of fixed and variable expansion devices, and summarizes results of the

analyses performed to compare them. This paper analyzes a broad spectrum of

strategies for actively or passively controlling the inlet state of fixed‐geometry

expansiondevicessuchascapillarytubeandThermostaticexpansiondevice,tomatch

compressormassflowrateswithminimalperformancedegradationinanefficientR12

refrigerationsystem.ATXV(ThermalExpansionValve)systemwasselectedasperload

requirementandtypeofrefrigerant.Resultsyieldedinsightsthatcanbegeneralizedto

other refrigerants and systems. TXV were found to produce and control degree of

superheatofrefrigerant,higherefficiencythancapillarytubesacrosstheentirerangeof

operatingconditions,althoughthedifferencecanbemitigatedbyproperchoiceofthe

latter’slengthanddiameter.

INDEX TERMS: capillary tube; thermostatic expansion valve; fixed and variable

restriction;cop;

1. INTRODUCTION

Theselectionoftheexpansiondeviceis

of particular importance to the

operation of the refrigeration system

because it regulates refrigerant flow

into the evaporator. An expansion

device which is misapplied or

incorrectlysizedwillordinarilyresultin

operationaldifficultiesandpoorsystem

AMOL A. GAWALI et al DATE OF PUBLICATION: JUNE 28, 2014

ISSN: 2348-4098 VOLUME 02 ISSUE 05 JUNE 2014

INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY- www.ijset.in 327

performance. For example, an

undersized expansion device will

prevent sufficient refrigerant from

flowing into the evaporator causing a

reduction in the design cooling

capability of the system. An oversized

expansion device may allow too much

refrigerant into the evaporator causing

liquid refrigerant to flow back to the

compressor.Capillarytubesareusedto

expand the refrigerant from the

condenser pressure to the evaporator

pressure in low capacity refrigerating

machinessuchasdomesticrefrigerators

andwindowtyperoomairconditioners.

It also balances the systempressure in

the refrigeration cycle however; it has

no provision to adjust the mass flow

rate when load conditions changes. In

spite of this fact, capillary tubes are

preferredinsmallcapacityrefrigerating

machines, where the load is fairly

constant due to its several advantages

such as simplicity, low cost, zero

maintenance, and requirementofa low

starting torque motor to run the

compressor.Fig1showssimplecapillary

tube.Thethermostaticexpansionvalves

provide an excellent solution to

regulatingrefrigerant flow intoadirect

expansion type evaporator. The TEV

regulates refrigerant flow by

maintaininganearlyconstantsuperheat

at the evaporator outlet. Fig 2 shows

thermostatic expansion valve. As

superheatattheevaporatoroutletrises

due to increased heat load on the

evaporator, the TEV increases

refrigerantflowuntilsuperheatreturns

to the valve’s setting. Conversely, the

TEVwilldecreaserefrigerantflowwhen

superheat lowers as a result of a

decreased heat load on the evaporator.

Theeffectofthistypeofregulationisit

allows the evaporator to remain as

nearly fully active aspossibleunder all

loadconditions.

2. EXPANSIONDEVICEFUCTION

The basic function of expansion device

usedinrefrigerationsystem(1)Reduce

pressure from condenser pressure to

evaporator pressure, and (2) regulate

the refrigerant flow from the high‐

pressure liquid line into theevaporator

atarateequaltotheevaporationratein

the evaporator. Under ideal conditions,

themass flow rateof refrigerant in the

system should be proportional to the

cooling load sometimes; the product to

be cooled is such that a constant

evaporator temperature has to be

maintained. In other cases, it is

desirable that liquid refrigerant should

notenterthecompressor.Insuchacase,

themass flowratehas tobe controlled




insuchamannerthatonlysuperheated

vapor leaves the evaporator. Again, an

ideal refrigeration system should have

the facility to control it in such a way

that the energy requirement is

minimum and the required criterion of

temperature and cooling load are

satisfied. Some additional controls to

control the capacity of compressor and

thespacetemperaturemayberequired

inaddition,soastominimizetheenergy

consumption.

The expansion devices used in

refrigeration systems can be divided

into fixed opening type or variable

opening type. As the name implies, in

fixed opening type the flow area

remainsfixed,whileinvariableopening

type the flow area changes with

changingmassflowrates.Capillarytube

belongstothefixedopeningtype,while

the thermostatic expansion valve

belongstothevariableopeningtype.

2.1CAPILLARYTUBE

Acapillarytubeisalong,narrowtubeof

constant diameter. Typical tube

diameters of refrigerant capillary tubes

range from 0.5 mm to 3 mm and the

length ranges from 1.0 m to 6 m. The

pressure reduction in a capillary tube

occursdue to the following two factors

(1) therefrigeranthas toovercomethe

frictional resistance offered by tube

walls this leads to somepressuredrop.

(2) The liquid refrigerant flashes

(evaporates) intomixture of liquid and

vapor as its pressure reduces. The

densityofvapor is less than thatof the

liquid. Hence, the average density of

refrigerant decreases as it flows in the

tube. (3) The mass flow rate and tube

diameter (hence area) being constant,

the velocity of refrigerant increases

since=ρVA.The increase invelocityor

acceleration of the refrigerant also

requirespressuredrop

Figure1:CapillaryTube

2.2 THERMOSTATIC EXPANSION

VALVE

Thermostatic expansion valve is the

most versatile expansion valve and is

most commonly used in refrigeration

systems. It is variable opening type

expansion device. A thermostatic

expansion valve maintains a constant

degree of superheat at the exit of




evaporator;henceitismosteffectivefor

dry evaporators in preventing the

slugging of the compressors since it

does not allow the liquid refrigerant to

enter the compressor. The schematic

diagramofthevalveisgiveninFigure2.

This consists of a feeler bulb that is

attached to the evaporator exit tube so

thatitsensesthetemperatureattheexit

of evaporator. The feeler bulb is

connectedtothetopofthebellowsbya

capillary tube. The feeler bulb and the

narrow tube contain some fluid that is

calledpowerfluid.Thepowerfluidmay

be the same as the refrigerant in the

refrigeration system, or it may be

different.Incaseit isdifferentfromthe

refrigerant, then the TEV is called TEV

withcrosscharge.

Figure2:ThermostaticExpansionValve

3. EXPERIMENTSET‐UP

Asetupmanufacturedtoexperimentally

investigatetheperformanceofcapillary

tubeandThermostaticExpansionvalve

for refrigerant R‐12.Experiment setup

consist of four major part of

refrigeration system such as

compressor, which compress

refrigerant,condenserwhichrejectsthe

heat from refrigerant at constant

pressure .expansion device which drop

down the temperature and pressure of

the refrigerant. And finally evaporator

whichisabsorbsheatfromrefrigerated

space. All the component of the

refrigeration system is displayed on

portable the metallic panel. The unit

consist 0.3 TR capacity compressor,

condenser thermostatic Expansion

Valveandcapillarytubeandevaporator.

Here for the experiment purpose two

expansion devices capillary and

thermostatic expansion valve are used

in system.fig 3, shows line diagram of

simple vapor compression system.

Evaporator coil is deep in water

calorimeter to so that the water

temperaturelowersdownduetolossof

heatenergyduetoevaporationprocess.

Heaterisprovidingatthebottomofthe

calorimeter which offers the heat load

which is balanced by the refrigeration

effectproducebythesystem.

Calorimeter contain sufficient of water

that the evaporative coils totally

immersed. Temperature of water




presentincalorimeterismeasuredwith

the help of digital temperature

indicator. Pressure gauges are attached

at inlet andoutlet of condenser aswell

asEvaporator.Forsafetyofcompressor

purpose high temperature and low

temperaturecutoffswitchisprovide

Table‐1:SpecificationofExperimentSet‐up

Sr.

No

Parameters Description

1 Type RefrigerationTutor

2 Refrigerant R12

3 Capacity 0.33TR

4 Compressor Hermetically Sealed,

single cylinder

reciprocating

5 Condenser Finnedcoils,Aircooled

6 Expansion

device

CapillarytubeandTXV

7 Evaporator Baretubetype

Figure3:VaporCompressioncycle

Figure4:p‐hDiagramforR‐12

Figure5:ActualSetupLineDiagram

4. EXPERIMENTREADINGSFOR

CAPILLARY

Thereadings forcapillary tube is taken

by allowing flow of refrigerant R‐12

throughcapillarytubewhilerefrigerant

flowtoTXVisrestrictedwiththehelpof

manual valve. This reading is use to

calculate system actual, theoretical and

CarnotCOP.




Table‐2:CapillaryTubeReadings

S.No. Parameter Unit Readings

1 Condenserpressurein bar 11.5

2 Condenserpressureout bar 11.2

3 Evaporatorpressurein bar 3.2

4 Evaporatorpressureout bar 3.0

5 Refrigerantflowrate lph 28

6 Condenserinlettemperature 0C 53

7 Condenseroutlettemperature 0C 30

8 Evaporatorinlettemperature 0C 3

9 Evaporatoroutlettemperature 0C 12

10Timefor10revolutionofcompressor

metersec 62

11Timefor10revolutionofHeater

(energy)metersec 32

4.1 CALCULATION FOR CAPILLARY

TUBE

FromP‐hchartofR‐12showninFigure

4.

h1=190kJ/kg,

h2=230kJ/kg,

h3=h4=90kJ/kg,

Carnotcop=4.15

Theoreticalcop=2.5

Actualcop=1.67




Table‐3:ThermostaticExpansionValveReadings

S.No. Parameter Unit Readings

1 Condenserpressurein bar 10.7

2 Condenserpressureout bar 10.5

3 Evaporatorpressurein bar 2.4

4 Evaporatorpressureout bar 2.2

5 Refrigerantflowrate lph 16

6 Condenserinlettemperature 0C 58

7 Condenseroutlettemperature 0C 34

8 Evaporatorinlettemperature 0C ‐3

9 Evaporatoroutlettemperature 0C 16

10Time for 10 revolution of

compressormetersec 70

11Time for 10 revolution of Heater

(energy)metersec 36

4.2 CALCULATION FOR

THERMOSTATICEXPANSIONVALVE

FromP‐hchartofR‐12,showninfigure

4.

h1=190kJ/kg,

h2=220kJ/kg,

h3=h4=80kJ/kg,

Carnotcop=5.2

Theoreticalcop=3.6

Actualcop=1.944

4.3 FORMULAE USED FOR

CALCULATION

Inputgivenbycompressor

Wcomp,ip=(Nc×3600)/(tc×3200)

Inputgivenbyheater




Wheater,ip=(Nh×3600)/(th×3200)

Carnotcop

(COP)Carnot=TL/(TH‐TL)

Actualcop

(COP)Actual=Wheater,ip/Wcomp,ip

Theoreticalcop

(COP) theoretical =Refrigerating effect /

compressorwork

=(h1‐h4)/(h2‐h1)

4.4 NOMENCLATURE AND

SUBSCRIPTS

W=workdone

h=enthalpy

Cop=coefficientofperformance

Comp=compressor

ip=input

L=lower

H=higher

1,2,3,4=enthalpypointvalue.

5. CONCLUSION

1) A TXV equipped refrigeration

system provides energy saving.TXV

have shown that they maintain higher

levelofefficiencyevenwhenrefrigerant

charge is lower than the manufactures

specification.

2) Fixed expansion devices, such

ascapillary tubes, work at one preset

levelandhavenoabilitytocompensate

forloadchanges

3) Variations of capacity over the

ambient temperaturerangeof260C to

55 0C can cause a performance loss of

85% with a cap tube system. A well

tuned expansion valve systemwill lose

less than one half this amounts, while

maintaining better compressor

temperaturecontrol.

4) Thermostatic expansion valve

Maximum efficiency over a wide

temperature and load range, it gives

improved refrigerant return to the

compressor assures better cooling at

high temperatures and reduces the

possibility of liquid sluggingwhich can

destroythecompressor

5) Carnot cop is higher than

theoreticalcopandactualcopincaseof

both thermostatic expansion valve and

capillarytube.

6) Experimental results shows

thermostaticexpansionvalvehashigher

Carnot,, theoreticalandActualcopthan

capillarytube.TXVhaslesscompressor

workthancapillarytube.




7) It was found that the energy

consumption of the thermostatic

expansionvalvesystemwasonly lower

thanthatofthecapillarytubesystemat

higher cooling loads and at lower

coolingcapacities

8) During experiment it is occurs

that thermostatic expansion valve able

to drop down more pressure than the

capillary which is produce more

refrigeranteffectforthesystem.

9) During experiment it is occurs

that thermostatic expansion valve able

to control degree of superheat of

refrigerant which causes reduction in

compressorwork and energy saving of

system.

ACKNOWLEDGEMENTS

I with great pleasure take this

opportunitytoexpressmydeepsenseof

gratitude towardsWalchand College of

Engineering,Sangli..Forallowingmeto

dothecasestudyworkon“Experiment

analysis and performance testing of

capillary tube and thermostatic

expansion valve”. I also would like to

thank my guide Prof. M.S.Joshi,

Department of Mechanical Engineering

for his valuable guidance and constant

inspirationduringthecompletionofthis

paper.

REFERENCES

[1]. Jackson B. Marcinichen, Claudio

Melo “Comparative analysis between a

capillary tube and an electronic

expansionvalveinahousehold”Federal

University of Santa

CatarinaInternational Refrigeration and

AirConditioningConference.Paper838,

March2006.

[2]. Mutalubi Aremu Akintunde,

”Effect of coiled capillary tube pitch on

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systemperformance”FederalUniversity

of Technology, Department of

Mechanical Engineering Akure, Ondo

State,Nigeriapp14‐22,July2007

[3]. Nishant P. Tekade, Dr. U. S.

Wankhede,”Selectionofspiralcapillary

tube for refrigeration appliances”

International Journal of Modern

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1430‐1434,May‐June2012.

[3]. Sporlan “Installing and servicing

thermostatic expansion valves”

bulletin10‐9,June2001

[4]. Marco Noro,Renato Lazzarin,

DanieleNardotto,“Electronicexpansion

valve vs thermal expansion valve”

ASHRAE Journal, pp. 34‐39, February

2009




[5]. Amit Kulkarni,Veerendra Mulay

and Dereje Agonafer, ”Effect of the

thermostatic expansion valve

characteristics on the stability of a

refrigeration system” 2002 IEEE Inter

Society Conference on Thermal

Phenomena,pp.403‐412

[6]. Schmidt, Roger, “Low

temperature electronic cooling”,

Electronics Cooling Magazine,

September2000,Vol.6,No.3.

[7]. Pakawat Kritsadathikarn,

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BIOGRAPHIES:

AmolA.GawalireceivedtheB.E.

and M. Tech degrees in

MechanicalEngineeringfromDr.

Babasaheb Ambedakar

UniversityandShivajiUniversity

in2010and2014,respectively.

Prof. Madhav S. Joshi received

the B.E. andM. Tech degrees in

Mechanical Engineering from

Shivaji University 1976 and

1979,respectively.Heisworking

as Associate professor in

WalchandcollegeofEngineering

since1980totilldate.

RupeshL.RautreceivedtheB.E.

and M. Tech degrees in

Mechanical Engineering from

Pune University and Shivaji

University in 2010 and 2014,

respectively.

Rahul A. Bhogare received the

B.E. and M. Tech degrees in

MechanicalEngineeringfromDr.

Babasaheb Ambedakar

University and MITCOE,

Kuthrud,Punein2010and2014,

respectively.




EXPERIMENT ANALYSIS AND PERFORMANCE TESTING OF CAPILLARY TUBE AND THERMOSTATIC EXPANSION VALVE

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