International Journal of Scientific & Engineering Research, Volume 3, Issue 10, October-2012 1

ISSN 2229-5518

A Performance comparison of vapour compression refrigeration system using various

alternative refrigerants

A.Baskaran, P.Koshy Mathews

Abstract — A performance analysis on a vapour compression refrigeration system with various refrigerants mixture of R152a, RE170, R600a, and R290 were done for various mixture ratios and their results were compared with R134a as possible alternative replacement. The results showed that all of the alternative refrigerants investigated in the analysis except R431A, [R 152a (29%), R290 (71%)] have a slightly higher performance coefficient (COP) than R134a for the condensation temperature of 500C and evaporating temperatures ranging between -300C and 100C.Refrigerant blend of R152a/RE170 (20/80 by wt%) instead of R134a was found to be a replacement refrigerant among other alternatives. The effects of the main parameters of performance analysis such as refrigerant type, degree of sub cooling and super heating on the refrigerating effect, coeffi cient of performance and volumetric refrigeration capacity were also investigated for various evaporating temperatures.

Index Terms — Refrigeration, Alternative Refrigerants, R152a, Di methylether, Propane, Isobutane, R134a

1 INTRODUCTION

——————————  ——————————
he ozone depleting potential (ODP) and global warm- ing potential (GWP) have become the most important criteria in the development of new refrigerants apart
from the refrigerants CFCs due to their contribution to ozone layer depletion and global warming. In spite of their high GWP, alternatives to refrigerants CFCs and HCFCs such as hydro fluoro carbon (HFC) refrigerants with the zero ODP and hydro carbon refrigerants (HC) have been preferred for use in many industrial and domestic applica- tions. The HFC refrigerants are considered as one of the six target greenhouse gases under Kyoto protocol of united nations frame work convention on climate change (UN- FCCC) In 1997 [1, 2]. Kyoto protocol was approved by many nations called for the reduction in emission of green house gas including HFC refrigerants. The presence of flor- ine atoms in HFC134a is responsible for the major envi- ronmental impact (GWP) with serious implications for the future development of the refrigeration based industries.
A number of investigators reported that GWP of HFC refrigerants is more significant even though it has less than CFC refrigerants. Fatosh and kafafy [3] theoretically assessed the mixture composed of 60% propane and 40% commercial butane is the best drop in substitute for HFC134a based domestic refrigerators. Park et al [4] tested two pure hydrocarbons and seven mixture composed of propylene, propane, HFC 152a and dimethylether as an alternative to HCFC22 in residential air conditioners and heat pumps. Their experimental results show that the coef- ficient performance (COP) of these mixtures was up to 5.7% higher than that of HFC22. Mani and Selladurai [5] per- formed experiments using a vapour – compression refrig- eration system with the new R 290/R600a refrigerant mix-
ture as a substitute refrigerant for CFC12 and HFC
134a.According to the results of their experiments, the re- frigerant R290/R600a had a refrigerating capacity 28.6% to

87.2% higher than that of R134a.B.O Bolaji [6] performed experimental study of R152a and R32 to replace R134a in a domestic refrigerator.

Nomenclature

atm Atmosphere

CFCS Chlorofluorocarbons

COP Coefficient of Performance GWP Global warming potential HCFCs Hydro chlorofluorocarbons HCs Hydrocarbons

HFCs Hydro fluorocarbons

ODP Ozone depletion potential

P Pressure kPa

RE Refrigirating effect, kJ Kg-1

MFR Mass flow rate, kgs-1

T Temperature, °C

W isentropic compression work kJ kg-1

VRC Volumetric refrigerating capacity, kJm-3

TR Ton of refrigeration

sh/sc super heating/sub cooling

Nsh/Nsc Non super heating/Non sub cooling

Subscripts

cod Condensing/Condenser evap evaporating/evaporater comp compressor

dis discharge

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According to the result of the experiments, the average COP obtained using R152a is 4.7% higher than that of R134a. G.D Mathur [7] conducts theoretical investigation to compare the COP of vapour compression refrigeration sys- tem using various refrigerants under conditions -60C evap- orator temperature and 480C condenser temperature. According to the results, the COP of the hydrocarbons in- creases from 6% to 9% than COP of R134a.
The present study mostly concentrates on a theo- retical investigation on the performance of the vapour compression refrigeration cycle. The refrigerant mixture R429A[RE170(60%), R152a(10%), 600a(30%)], R430A [R152a(76%), R600a (24%)], R431A [R152a (29%), R290(71%)],R435A [RE170(80%), R152a(20%)], R509A[R290(50%), R600a(50%)] and R510A [RE170(88%), R600a(12%)] are used as the working fluid for the compari- son with the conventional refrigerant R134a.The effects of the main parameters of performance analysis such as re- frigerant type, degree of sub cooling and super heating on the refrigerating effects, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures ranging between -300C and 50C and a constant condensation temperature of 500C.

2 METHOD OF ANALYSIS

The software CYCLE_D 4.0 vapour compression cycle design program was used for the analysis to find the performance of the system .The ideal refrigeration cycle is considered with the following conditions.
System cooling capacity (kW) = 1.00
Compressor isentropic efficiency = 1.00
Compressor volumetric efficiency = 1.00
Electric motor efficiency = 1.00
Pressure drop
In the suction line =0.0
In the discharge line =0.0
Evaporator: average sat. temp =-300C to +100C
Condenser: average sat. temp =500C
Super heat = 100C
Sub cooling = 50C
For comparison of the theoretical data, R134a is chosen in this paper as reference fluid due to its common usage in cooling system and prohibition by Kyoto protocol. The analysis of the variation of physical properties and per- formance parameters of pure and blend refrigerants such as evaporation pressure (Pevap), pressure ratio, isentropic compression work (W), refrigerating effect (RE), power per ton of refrigeration, volumetric refrigeration capacity (VRC), discharge temperature (TDis ), mass flow rate (MFR) and coefficient of performance (COP) are investigat- ed in this theoretical study and they are plotted against the evaporating temperature (Tevap) as shown in figures from
1 to 10. Table 1 and 2 show the operation results and devia-
tion of alternative refrigerants from the values of R134a.

3 THERMO PHYSICAL PROPERTIES

The changes in evaporating pressure (Pevap) and pressure ratio with the evaporation temperature (Tevap) were shown in fig 1 and 2 for listed refrigerants. The near- est pressure ratio of refrigerant substituted for R134a be- longs to R435A whose pressure ratio was 6.39% lower than that of R134a as shown in table 2 for the constant condensa- tion and evaporation temperatures of 500C and -100C re- spectively. In addition to this R431A [R 152a (29%), R290 (71%)] gives the lowest ratio as substitute for R134a accord- ing to the same table. It can be seen from fig 1 that the satu- rated vapour pressure for R509A was closer to the vapour pressure curve of the refrigerant R134a than others .Fig 3 and 4 show that the refrigerating effects (RE) increase with increasing evaporation temperature (Tevap) while the compressor power (Wcomp) decreases with increasing Tevap for the constant condensation temperature of 500C and the evaporation temperature ranging from -300C to
100C.

Fig.1. Evaporating Pressure vs evaporating temperature

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Fig. 2. Pressure Ratio vs evaporating temperature

Table.1

Operation on a standard vapour-compression cycle using R134a and various refrigerants at Tcod=50°C and Tevap=-10°C

with super heating 10°C and sub cooling 5°C

Table.2

Some deviation values of alternative refrigerants from R134a

R134a at Tcod = 50°C and Tevap = -10°C with super heating 10°C and sub cooling 5°C

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Fig.3. Refrigerating effect vs evaporating temperature

Fig. 4.Compression Work vs evaporating temperature

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Fig. 5.Coeffiecient performance vs Evaporation temperature

Fig.6. Compressor Power vs evaporating temperature

Fig.7. Power per ton of refrigeration vs evaporating temperature

Fig.8. Volumetric refrigerating capacity vs Evaporation temperature

Fig.9. Discharge temperature vs evaporating temperature

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Fig.10. Mass flow rate vs evaporating temperature

All of the tested refrigerants have much higher re- frigerating effect and isentropic compression work than R134a in fig 3, 4 and as shown in table 2.
The variation of the performance coefficients (COP) with evaporating temperatures (Tevap) is illustrated in fig 5. It Is found that the coefficient of performance (COP) increases as the evaporation temperature (Tevap ) increases for the constant condensation temperature of 500C and the evaporation temperature ranging from -300C to
100C. The performance coefficients (COP) of all the alternat-
ing refrigerants except R431a were found to be higher than
that of R134a.
The power needed for refrigeration with evapora- tion (Tevap) was shown in fig 6 and 7. The variation in vol- umetric refrigeration capacity, discharge temperature and mass flow rate were illustrated in fig 8, fig 9 and fig 10 in order to verify the advantages of cycle.
The cycle performance can be improved by the sub cooling and super heating applications. The comparisons of the super heating/sub cooling with the non-super heating/sub cooling were illustrated in figs from 11a to 11g for the re- frigerant blend of R435A.
The performance coefficient (COP) values of the super heat- ing / sub cooling case are found to be higher than those of the non-super heating sub cooling case. The reason for the improvement is the increase in the compressor inlet tem- perature and thus the increases in refrigerating effect and volumetric refrigerating capacity.
The thermo-physical properties restriction related to safety, environmental impact, and associated legislation are the

most significant factors in choosing a new refrigerant. Low viscosities of liquid and vapour phases, high liquid specific heat, high thermal conductivities of liquid and small tem- perature glide are the desired thermo physical properties of refrigerant mixture in the literature. As a result of the anal- ysis, R435A [RE170 (80%), R152a (20%)] instead of R134a seems to be the best alternative refrigerant.

Fig. 11-a Refrigerating effect vs evaporating temperature

Fig.11-b compression work vs evaporating temperature

Fig.11-c. Co-efficient of performance vs evaporating temperature

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Fig.11-d. Power per ton of refrigeration vs evaporating temperature

Fig.11-e.Volumetric refrigerating capacity vs evaporating temperature

Fig.11-f.Mass flow rate vs evaporating temperature

frigerants tested for R134a.The performance coefficient (COP) of the system, increases with increase in evaporating temperature for a constant condensing temperature in the analysis. All system including various refrigerant blends were improved by analyzing the effect of the super heating
/ sub cooling case. Better performance coefficient values (COP) than those of non-super heating /sub cooling case are obtained as a result of this optimization.

5. ACKNOWLEDGMENT

The work reported here was supported through the De- partment of Mechanical Engineering, P.A.College of Engi- neering and Technology, Pollachi-2.

6. REFERENCES

[1] Johnson, E, “Global warming from HFC”, Environ. Impact assessment

Rev, 18, 485-492. 1998.

[2] Wen – Tien Tasi, “An overview of environmental hazards and exposure and explosive risk of hydroflurocarbon HFCs”, Chemosphere, vol.61, pp.1539-47, 2005.

[3] Fatouh M and Kafafy M. El, “Experimental evaluation of a domestic refrigerator working with LPG”, Applied Thermal Engineering, vol.26, Iss.14-15, pp. 1427-1770, 2006.

[4] K.J. Park, T. seo. D.Jung performance of alternative refrigents for residen- tial air conditing applications, Applied energy, vol.84, pp. 985-991, 2007.

[5] K.Mani, V.Selladurai, Experimental analysis of a new refrigerant mixture

as drop in replacement for CFC12 and HFC 134a, International journal of thermal sciences, vol. 47,pp.1490-1495, 2008.

[6] B.O. Boloji, Experimental study of R152a and R32 to replace R134a in a domestic refrigerator, Energy, vol. 35, Iss. 9, pp. 3793-3798, Sept 2010.

[7] G.D.Mathur, Performance of vapour compression refrigeration system

with hydro carbons, proceedings of the 1996 international conference on ozone protection technologies, Washington, DC, pp. 835-844, USA 1996.

[8] CYCLE _D vapour compression cycle design. NIST Standard reference data base49-version4.0.Gaithersberg, MD: National institute of standards and technology (2004).

Mr. A. Baskaran

Assistant Professor

Department of Mechanical Engineering,

P.A.College of Engineering and Technology, Pollachi 642002, India

Email:boss120367@gmail.com

Fig.11-g.Compressor power vs evaporating temperature

4. CONCLUSIONS

In this study, an ideal vapor-compression system is used for the performance analysis of alternative new refrig- erant mixture as substitute for R134a. Considering the comparison of performance coefficients (COP) and pressure ratio of the tested refrigerants and also the main environ- mental impacts of ozone layer depletion and global warm- ing, refrigerant blend R435A [RE170 (80%), R152a (20%)] were found to be the most suitable alternative among re-

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Dr. P. Koshy Mathews

Dean

Department of Mechanical Engineering,

Kalaivani College of Technology, Coimbatore 641105, India

Email:pkoshymathews@yahoo.co.in