Performance Analysis of Vapour Compression Refrigeration ... · PDF file25 Int. J. Mech. Eng. & Rob. Res. 2013 Jyoti Soni and R C Gupta, 2013 PERFORMANCE ANALYSIS OF VAPOUR COMPRESSION

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Int. J. Mech. Eng. & Rob. Res. 2013 Jyoti Soni and R C Gupta, 2013

PERFORMANCE ANALYSIS OF VAPOURCOMPRESSION REFRIGERATION SYSTEM WITH

R404A, R407C AND R410A

Jyoti Soni1* and R C Gupta1

*Corresponding Author: Jyoti Soni, [email protected]

This paper provides a detailed exergy analysis for theoretical vapour compression refrigerationcycle using R404A, R407C and R410A. The equations of exergetic efficiency and exergydestruction for the main system components such as compressor, condenser expansion device,liquid-vapour heat exchanger and evaporator are developed. The relations for total exergydestruction in the system, the overall exegetic efficiency of the system and Exergy DestructionRatio (EDR) related to exergetic efficiency are obtained. Also, an expression for Coefficient ofPerformance (COP) of refrigeration cycle is developed. The investigations shows that variousresults are obtained for the effect of evaporating temperatures, condensing temperatures, degreeof subcooling and effectiveness of liquid-vapour heat exchanger on COP, exergetic efficiencyand EDR of theoretical vapour compression refrigeration cycle.

Keywords: Exergetic analysis, Refrigeration system, Modelling, R404A, R407C, R410A

INTRODUCTIONIn the past decades, the Ozone DepletionPotential (ODP) and Global WarmingPotential (GWP) have becomes the dominantenvironmental issues, caused by the leakagesof the CFC and HCFC refrigerants. TheMontreal protocol (UNEP, 1997) declared thephasing out of CFC’s and HCFC’s asrefrigerants that deplete the ozone layer(ODP) (UNEP, 1997). The Kyoto protocol(UNFCC, 2011) encouraged promotion of

ISSN 2278 – 0149 www.ijmerr.comVol. 2, No. 1, January 2013

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Int. J. Mech. Eng. & Rob. Res. 2013

1 Jabalpur Engineering College, Gokulpur, Ranjhi, Jabalpur 482011, Madhya Pradesh, India.

rules for sustainable development andreduction of Global Warming Potential(GWP) including the regulations of HCFC’s(United Nations, 2011). Both of CFC andHCFC have high ODP and GWP. Becauseof their high GWP, alternatives to refrigerantsCFC and HCFC such as azeotropic mixturesrefrigerants with their zero ODP have beenpreferred for use in many industrial anddomestic applications intensively for adecade.

Research Paper

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Various researches have suggesteddifferent HC, HFC and HCFC blends aspotential substitutes for CFCs and comparedthe performance of these substitutes eithertheoretically or experimentally. Douglas et al.(1999) describes the development andapplication of a cost-based method forcomparing alternative refrigerants applied toR22 systems. A computational model basedon this method was used to analyze theperformance of several leading R22replacements candidates for window airconditioners. From the investigations it wasrevealed that for the optimized systems, all thealternatives had system costs that were withinabout 4% of those for R22. Also, differencesbetween most of the alternative refrigerantswere smaller than the uncertainties in theanalysis. Havelsky (2000) conducted anexperimental analysis for R12 replacementswith the influence on energy efficiency andglobal warming expressed by the values ofCoefficient of Performance (COP) and TotalEquivalent Warming Impact (TEWI). PresentedExperimental analysis, relate the use ofrefrigerants R134a, R401A, R409A, R22 andthe mixture of R134a with R12 to the values ofCOP and TEWI of refrigerating system incomparison with R12 application. Their resultsshowed that the use of R134a, R401A andR409A refrigerants enables the values of TEWIin comparison with R12 application. Aprea andGreco (2002) presents an experimentalinvestigation for R22 replacements in vapourcompression plant with most widely useddrop-in substitute i.e. the zeotropic mixtureR407C. The experimental analysis was carriedout with the help of exergetic approach. Theexergetic performance of the individualcomponents of the plant has been analyzed,

in order to pinpoint those contributing most tothe decrease in the exergetic performance ofR407C. Aprea et al. (2004) conducted anexperimental analysis to study theperformances of a vapour compression plantworking both as a water chiller and as a heatpump, using as refrigerant fluids R22 and itssubstitute R417A. The results revealed thatR22 gives best performances in comparisonwith R417A in terms of COP, exergeticefficiency and exergy destroyed in thecomponents. Akhilesh and Kaushik (2008)present a detailed exergy analysis of an actualvapour compression refrigeration cycle. Acomputational model has been developed forcalculating the COP, exergetic efficiency,exergy destruction and efficiency defects forR502, R404A and R507A. The results of thisinvestigations revealed that R507A is a bettersubstitutes to R502 than R404A. Comakliet al. (2009) experimentally investigated theeffects of gas mixture rate, evaporator air inlettemperature (from 24 to 32), evaporator airmass flow rate (from 0.58 to 0.74), condenserair inlet temperature (from 22 to 34) andcondenser air mass flow rate (from 0.57 to0.73) on the COP and the exergetic efficiencyvalues of vapour compression heat pumpsystems. The investigation has been done forrefrigerants R22 and R404A five of their binarymixtures which contain about 0%, 25%, 50%,75% and 100% mass fractions of R404A weretested. It was observed that the most effectiveparameters are found to be condenser air inlettemperature on COP and exergetic efficiency.Miguel et al. (2010) presents an exergyanalysis of the impact of direct replacements(retrofit) of R12 with the zeotropic mixtureR413a on the performance of a domesticvapour compression refrigeration system,

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originally designed to work with R12. Theresults of this experimental investigationshowed that overall energy and exergyperformance of the system working with R413Ais consistently better than that of R12.Venkataramanamurthy and Senthil (2010)conducted an experimental test for the analysisthe comparisons of energy, exergy flow andsecond law efficiency of R22 and its substitutesR-436b in vapour compression refrigerationsystem. The investigations present the effectsof the evaporating temperatures on the exergyflow losses and second law efficiency andcoefficient of performance of a vapourcompression refrigeration cycle. Bilal andSyed (2011) investigated performancedegradation due to fouling in a vapourcompression cycle for various applications.For the analysis consider the two sets ofrefrigerants depending upon the assumptionand their some properties. Considering the firstset of refrigerants R134a, R410A and R407Cwhile second set include the refrigerants ofR717, R404A and R290. From a first lawstandpoint, the COP of R134a alwaysperforms better than R410A and R407C unlessonly the evaporator is being fouled. From asecond law standpoint, the second lawefficiency of R134a performs the best in allcases. From a first law standpoint, the COPof R717 always performs better than R404Aand R290 unless only the evaporator is beingfouled. From a second law standpoint, thesecond law efficiency of R717 performs thebest in all cases. Volumetric efficiency ofR410A and R717 remained highest under allthe respective conditions. Furthermore,performance degradation of evaporator haslarger effect on compressor power

consumption while the performancedegradation of condenser has larger effect onCOP of the vapour compression cycle.

In this paper exergetic approach is usedto analysis the performance of theoreticalvapour compression refrigeration cycle usingR404A, R407C and R410A. The equationsof exergetic efficiency and exergy destructionfor the main system components such ascompressor, condenser expansion device,liquid-vapour heat exchanger and evaporatorare developed. The relations for total exergydestruction in the system, the overall exergeticefficiency of the system and EDR related toexergetic efficiency are obtained. Also, anexpression for COP of refrigeration cycle isdeveloped. This investigations shows thatresults are obtained for the effects ofevaporating temperatures, condensingtemperature, degree of subcooling andeffectiveness of liquid-vapour heat exchangeron COP, exergetic efficiency and EDR oftheoretical refrigeration cycle. Commonly,simple vapour compression refrigerationsystems are used for comfort cooling and coldstorage application. Depending upon theapplications evaporating temperature variesfrom –50 °C to 7 °C (Bilal and Syed, 2011).The scientists investigate moreenvironmentally friendly refrigerants to resolvethe problems of ODP and GWP. Currently, thefollowing three refrigerants are being used asalternatives to CFC in various applications:R404A, R407C and R410A. Though, thesethree refrigerants are completely harmless toozone layer, but sometimes they can add toglobal warming due to their leaks. The maincharacteristics of the tested refrigerants asshown in Table 1.

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EXERGY ANALYSISA modified vapour compression refrigerationsystem consists of five components such asevaporator, liquid-vapour heat exchanger,compressor, condenser and expansiondevice. All the components connected in aclosed loop through piping that has heattransfer with the surrounding can be shown inFigure 1. At point 11, refrigerant leaves theevaporator at a low pressure, low temperature,saturated vapour and enter the liquid vapourheat exchanger where it absorbs the heat fromhigh pressure-temperature refrigerant flowsfrom the condenser. At state 1, the refrigerantfrom the liquid-vapour heat exchanger enterinto compressor through the suction line whereboth temperature and pressure increases. Thisprocess can be shown in Figure 2. At state 2,it leaves the compressor at a high pressure,high temperature, superheated vapourconditions and enter the condenser where itreject heat to surrounding medium at constantpressure after undergoing heat transfer in thedischarge line. Refrigerant leaves thecondenser at state 3, as a high pressure,medium temperature, saturated liquid and

Refrigerant R404A R407C R410A

Molar Mass 97.60 86.20 72.58

Boiling Point (°C) –46.45 –43.56 –51.6

Critical Temperature (°C) 72.07 86.74 72.5

Critical Pressure (bar) 3.7315 4.6191 4.95

Critical Density (kg/m3) 484.5 527.30 500

Critical Volume (m3/kg) 0.00206 0.00190 0.00205

Ozone Depletion Potential 0 0 0

Global Warming Potential 3859 1526 1725

Certainty Class A1 A1 A1

Table 1: The Main Characteristicsof the Tested Refrigerants

Source: Mohanraj et al. (2009)

enter the liquid-vapour heat exchanger at state33, where it rejects the heat to low pressure-temperature refrigerant. The expansion deviceallows to flowing the liquid refrigerant atconstant enthalpy from high pressure to lowpressure. At state 4, it leaves the expansionvalve as a low temperature, low pressure, andliquid-vapour mixture and enters the

Figure 1: Schematic of Typical VapourCompression Refrigeration System

with a Liquid-Vapour Heat Exchanger

Figure 2: Pressure-Enthalpy DiagramShowing Effect of an Idealized Liquid-

Vapour Heat Exchanger

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evaporator where it absorbs the heat atconstant pressure from the space to be cooledand changed into saturated vapour and cycleis completed.

For analysis the performance of vapourcompression refrigeration system, followingassumption are made:

• Degree of subcooling of liquidrefrigerant in liquid-vapour heatexchanger (T

sub) = 5 °C.

• Mechanical efficiency of compressor(

mech) = 75%.

• Electrical efficiency of compressor(

el) = 75%.

• Difference between evaporator andspace temperature (T

r – T

e) = 20 °C.

• Effectiveness of liquid vapour heatexchanger () = 0.8.

• Evaporator temperature Tevap

(in °C)ranging from –50 °C to 0 °C.

• Condenser temperature Tcond

(in °C)= 40 °C, 55 °C.

• Mass flow rate of refrigerant (mr) =

1 kg/s

• Dead state temperature (T0) = 30 °C.

• There is no pressure loss in pipelines.

• In all components steady stateoperations are considered.

The energy analysis based on first law ofthermodynamic, the performance of vapourcompression refrigeration system can bepredicted in terms of Coefficient ofPerformance (COP), which is defined as theratio of net refrigerating effect produced by therefrigerator to the work done by thecompressor. It is expressed as:

w

QCOP e

22

41

hh

hhCOP

...(1)

The modern approach based on secondlaw of thermodynamic, i.e., exergy analysiscan be used to measures the performanceof the vapour compression refrigerationsystem. This analysis derives the concept ofexergy, which is always decreasing due tothermodynamic irreversibilities. Exergy is themaximum useful work that could be obtainedfrom the system at a given state in a specifiedenvironment. Exergy balance for a controlvolume undergoing steady state process isexpressed as:

outxinxd memeEi

outin TTQTTQ /1/1 00

W ...(2)

Exergy Destruction (ED) in the SystemComponents

Exergy destruction in each component of thecycle is calculated as:

Exergy destruction in Evaporator

114

01 xr

exd ET

TQEE

e

rer T

TQSThm 0

404 1

11011 SThmr ...(3)

Exergy destruction in Compressor

21 xxd EWEEcomp

30


elmech

r

wSTm

20

202 SThmr ...(4)

Exergy destruction in Condenser

32 xxd EEEc

303202 SThmSThm rr

cc T

TQ 01 ...(5)

Exergy destruction in Throttle valve

433 xxd EEEt

40433033 SThmSThm rr ...(6)

Exergy destruction in liquid vapour heatexchanger

111331 xxxxd EEEEEivhe

111333 hhhhmr

1113330 SSSST ...(7)

Total Exergy Destruction

Total exergy destruction in the system is thesum of the exergy destruction in differentcomponents of the system and is given by

ivhetccompei dddddd EEEEEE ...(8)

Now, total exergy supplied is given by:

idEEPEF ...(9)

For refrigeration system, product is theexergy of the heat abstracted into theevaporator from the space to be cooled attemperature T

r, i.e.

re T

TQEP 01 ...(10)

Exergetic Efficiency (ex)

EF

EP

fuelofExergy

productinExergyex ...(11)

and exergy of fuel is actual compressor workinput, W. Hence exergetic efficiency is givenby:

W

TT

Qr

e

ex

01 ...(12)

Exergy Destruction Ratio (EDR)

Exergy destruction ratio is the ratio of the totalexergy destruction in the system to the exergyin the product and it is given by

EP

EDEDR total

EDR related to the exergetic efficiency givenby:

11

ex

EDR ...(13)

RESULTS AND DISCUSSIONFigures 3-4 shows the effects of evaporatingtemperatures on coefficient of performance.With increase in evaporator temperature, thepressure ratio across the compressordecreases, causing work done by thecompressor decrease and cooling capacityincreases due to increase in refrigeratingeffect. Hence, the combined effect of these twofactors increases the COP of the vapourcompression refrigeration system. R407Cpresents the maximum COP among all the

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refrigerants corresponding to evaporator andcondenser temperatures considered. R404Ashows better COP than R410A at bothcondenser temperatures, i.e., at 40 °C and 55°C. The maximum difference observedbetween COPs of R404A and R410A is4.03% at 55 °C at higher end of evaporatortemperatures. The COP of R407C is 7-14%higher than the COP for R404A and R410A at40 °C condenser temperature. This differenceis increases to 8-18% at 55 °C condensertemperature.

i.e. , r

e T

TQ 01 . With increase in evaporator

temperature Qe increases whereas the term

rT

T01 reduces. Second parameter is the

compressor work required by compressor Wwhich decreases with increase in evaporatortemperature. Both terms Q

e and W have

positive effect on increase of exergetic

Figure 3: Effect of EvaporatingTemperatures on COP

Figures 4-5 shows the effect of evaporatortemperatures on exergetic efficiency (

ex) and

EDR. With increase in evaporatortemperatures exergetic efficiency increases tillthe optimum evaporator temperature andbeyond this optimum temperature itdecreases. The optimum evaporator is thetemperature at which maximum exergeticefficiency is obtained. The curves trend forEDR almost reverses to curves of exergeticefficiency. The rise and fall of the exergeticefficiency, depends upon the two parameters.First parameter is the exergy of cooling effects,

Figure 4: Effect of EvaporatingTemperatures on Exergetic Efficiency

Figure 5: Effect of EvaporatingTemperatures on EDR

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efficiency whereas the term rT

T01 has

negative effect on increase of exergeticefficiency. The combined effects of these twoparameters, increases exergetic efficiency tillthe optimum evaporator temperature andbeyond the optimum temperature decrease.Because of exergetic efficiency is inverselyproportional to EDR; the curves trend for EDRalmost reverses to curves of exergeticefficiency. With increases in evaporatingtemperatures, EDR decreases till the optimumevaporator temperature and beyond thisoptimum temperature it increase. Theoptimum evaporator is the temperature atwhich minimum EDR is obtained. Theexergetic efficiency of R407C is 10-18%higher than R404A and 14-20% higher thanR410A at 40 °C condenser temperature. Thecorresponding values at 55 °C condensertemperature are 13-20% and 15-21% higher,respectively, for R407C. At both 40 °C and55 °C condensers temperatures, R407C isbetter than R404A and R410A. It also confirmsthat with increase in condenser temperaturethe difference among the exergetic efficiencyof R407C, R404A and R410A increases.

Figures 6-8 presents the effect of degreeof subcooling on COP, exergetic efficiency andEDR. It is evident that increase in degree ofsubcooling increases the cooling capacitybecause of increase in refrigerating effect andthere is no change in compressor work, henceCOP increases. From the study, it is evidentthat increase in COP increases the exergeticefficiency and reduces the EDR. The rate ofincrease in COP is approximately 0.99%/°C,0.7%/°C, and 0.85%/°C of subcooling in caseof R404A, R407C and R410A.

Figure 6: Variation of COP with Degreeof Subcooling

Figure 7: Variation of Exergetic Efficiencywith Degree of Subcooling

Figure 8: Variation of EDR with Degreeof Subcooling

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The rate of increase in exergetic efficiency isapproximately 1%/ , 0.73%/ and 0.84%/ forR404A, R407C and R410A. The total increasein exergetic efficiency for R404A, R407C andR410A is 10.52%, 7.55% and 8.71% for 10subcooling

Figures 9-11 shows the effect ofeffectiveness of liquid-vapour heat exchangeron COP, exergetic efficiency and EDR. Withincrease in effectiveness of liquid-vapour heatexchanger COP and exergetic efficiency

reduces whereas EDR increase. The totalCOP decreases by 17.39% and exergeticefficiency decreases by 9.05% for R407C. Thetotal COP decreases by22.82% and exergeticefficiency decreases by 5.85% for R410A. Thetotal COP decreases by 20.91% and exergeticefficiency decreases by 6.05% for R404A.

CONCLUSIONA computational model based exergy analysisis presented for the investigation of the effectsof evaporating temperatures, condensertemperature, degree of subcooling, andeffectiveness of the liquid vapour heatexchanger on the COP, exergetic efficiencyand EDR of the vapour compressionrefrigeration cycle for R404A, R407C andR410A. The conclusions present in thisanalysis are given as follows:

• The COP and exergetic efficiency ofR407C are better than that of R404A andR410A. The EDR of R410A is higher thanthat of R407C and R404A. This analysisperformed at condenser temperatures40 °C and 50 °C and evaporatortemperature ranging from 50 °C to 0 °C.

Figure 9: Effect of Effectiveness of Liquid-Vapour Heat Exchanger on COP

Figure 10: Effect of Effectivenessof Liquid-Vapour Heat Exchanger

on Exergetic Efficiency

Figure 11: Effect of Effectiveness ofLiquid-Vapour Heat Exchanger on EDR

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• For all refrigerants, i.e., R404A, R407C andR410A, COP and exergy efficiency improveby subcooling of high pressure condensedliquid refrigerant. The rate of increase inCOP is approximately 0.99%/°C, 0.7%/°C,and 0.85%/°C of subcooling in case ofR404A, R407C and R410A. The rate ofincrease in exergetic eff iciency isapproximately 1%/°C, 0.73%/°C and0.84%/°C for R404A, R407C and R410A.The total increase in exergetic efficiency forR404A, R407C and R410A is 10.52%,7.55% and 8.71% for 10 °C subcooling.

• With increase in dead state temperaturesexergetic efficiency increases and EDRreduces while coefficient of performanceremains constant. The curves trends of allrefrigerants are identical and their curvesfor both exergetic efficiency and EDR arenearly overlapping. The exergetic efficiencyof R-407C is 0.3-0.85% higher than R404Aand1.8-2.6% higher than R410A forconsidered range of dead statetemperatures.

• With increase in effectiveness of liquid-vapour heat exchanger COP and exergeticeff iciency decreases while EDRincreases. The total COP decreases by17.39% and exergetic eff iciencydecreases by 9.05% for R407C. The totalCOP decreases by 22.82% and exergeticefficiency decreases by 5.85% for R410A.The total COP decreases by 20.91% andexergetic efficiency decreases by 6.05%for R404A.

REFERENCES1. Akhilesh Arora and Kaushik S C (2008),

“Theoretical Analysis of a Vapour

Compression Refrigeration System withR502, R404A and R507A”, InternationalJournal of Refrigeration , Vol. 31,pp. 998-1005.

2. Aprea C and Greco A (2002), “AnExergetic Analysis of R22 Substitution”,Applied Thermal Engineering, Vol. 22,pp. 1455-1469.

3. Aprea C, Mastrullo R and Renno C (2004),“An Analysis of the Performance of aVapour Compression Refrigeration PlantWorking Both as a Water Chiller and aHeat Pump Using R-22 and 417A”,Applied Thermal Engineering, Vol. 24,pp. 487-499.

4. Bilal Ahmed Qureshi and Syed M Zubair(2011), “Performance Degradation of aVapour Compression RefrigerationSystem Under Fouled Conditions”,International Journal of Refrigeration,Vol. 34, pp. 1016-1027.

5. Comakli K, Simsek F, Comakli O andSahin B (2009), “Determination ofOptimum Conditions R-22 and R404aRefrigerant Mixtures in Heat Pumps UsingTaguchi Method”, Applied Energy,Vol. 86, pp. 2451-2458.

6. Douglas J D, Braun J E, Groll E A and TreeD R (1999), “A Cost Method ComparingAlternative Refrigerant Applied to R-22System”, International Journal ofRefrigeration, Vol. 22, pp. 107-125.

7. Havelsky V (2000), “Investigation ofRefrigeration System with R12 RefrigerantReplacements”, Applied ThermalEngineering, Vol. 20, pp. 133-140.

8. Miguel Padilla, Remi Revellin and JocelynBonjour (2010), “Exergy Analysis of

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R413A as Replacement of R12 in aDomestic Refrigeration System”, EnergyConversion and Management, Vol. 51,pp. 2195-2201.

9. Mohanraj M, Jayaraj S andMuraleedharan C (2009), “EnvironmentFriendly Alternatives to HalogenatedRefrigerants—A Review”, InternationalJournal of Greenhouse Gas Control,Vol. 3, pp. 108-119.

10. United Nations (2011), Kyoto Protocol tothe United Nations Framework Conventionon Climate Change, available at http://

untccc.int//resource/docs/convkp/kpeng.pdf

11. United Nation Environment Programme(UNEPs) (1997), The Montreal Protocolon Substances that Deplete the OzoneLayer.

12. Venkataramanamurthy V P and SenthilKumar P (2010), “ExperimentalComparative Energy, Exergy Flow andSecond Law Efficiency Analysis of R22,R436b Vapour CompressionRefrigeration Cycles”, InternationalJournal of science and Technology,Vol. 2, No. 5, pp. 1399-1412.

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COP Coefficient of performance (non-dimensional)

EF Exergy rate of fuel (kW)

EL

Thermal exergy loss rate (kW)

W Work rate (kW)

EDR Exergy destruction ratio (non-dimensional)

s Entropy (kJ/kg K)

P Pressure drop (bar)

Ed

Exergy destruction rate (kW)

EP Exergy rate of product (kW)

Ex

Exergy rate of refrigerant (kW)

h Enthalpy (kJ/kg)

T Temperature (K)

Greek Notations

ex

Exergetic Efficiency

Effectiveness of the liquid vapour heat exchanger

Tsub

Degree of subcooling of liquid refrigerant in lvhe (K)

Tsup

Degree of superheating of vapour refrigerant in lvhe (K)

Subscripts

C Condenser

R Space temperature

E Evaporator temperature

Compressor

T Refrigerant throttle valve

O Dead state

APPENDIX

Nomenclature

Documents

Performance Analysis of Vapour Compression Refrigeration ... · PDF file25 Int. J. Mech. Eng. & Rob. Res. 2013 Jyoti Soni and R C Gupta, 2013 PERFORMANCE ANALYSIS OF VAPOUR COMPRESSION