International Journal of Scientific & Engineering Research, Volume 3, Issue 12, December-2012

ISSN 2229-5518

Performance Analysis of Vapour Compression Refrigeration Systems Using Hydrofluorocarbon Refrigerants

Dr. A.C. Tiwari and Shyam kumar Barode

Department of Mechanical Engineering, University Institute of Technology, RGPV, Bhopal-462024, India

Abstract: In this paper, the performances of four ozone-friendly Hydrofluorocarbon (HFC) refrigerants (R125, R134a, R143a and R152a) selected to replace R12 in a vapour compression refrigeration system were investigated experimentally and compared. The performance i n term of coefficient of performance (COP), refrigerating capacity (RC), and compressor work (We) were evaluated for the investigated refrigerants at various evaporating and condensing temperatures. The system performance increases as the evaporating temperature increases, but reduces as the condensing temperature increases. The results obtained showed that the investigated refrigerants confirmed that R152a and R134a have approximately the same thermodynamic performances similar to R12 while deviation of R125 and R143a were very large. But the best performance was obtained from the used of R152a in the system. As a result, R152a could be used as a drop-in replacement for R134a in vapour compression refrigeration system. The COP of R152a obtained was higher than those of R12, R125, R134a, R143a. Also, R152a offers the best desirable environmental requirements; zero Ozone Depleting Potential (ODP) and very low Global Warming Potential (GWP).

Key words: Hydro-Fluoro-Carbon, refrigerants, ozone-friendly, performance characteristics, refrigeration system.

1. Introduction

A class of chemical compounds called Chlorofluorocarbon (CFC) refrigerants has been in widespread use since the 1930s in such diverse applications as refrigerants for refrigerating and air-conditioning systems, blowing agents for plastic foams solvents for microelectronic circuitry and dry cleaning sterilants for medical instruments (Bolaji BO, 2005). The linkage of the CFC refrigerants to the destruction of the ozone layer, which has been established recently; is attributable to their exceptional stability because of which they can survive in the atmosphere for decades and ultimately diffusing to the rarefied heights where the stratospheric ozone layer resides (McMullan JT,2002). The inventors of these refrigerants could not have visualized the ravaging effects of the refrigerants on the ozone layer. They intentionally pursued refrigerants with the exceptional stability that was imposed as one of the necessary requirements of the ideal refrigerant they were called upon to invent (Cavallini A, 1996).
The primary requirements of the ideal refrigerant before the discovery of CFC refrigerants were as follow: it should have normal boiling point in the range of -40°C to 0°C; it
should be non-toxic; it should be non-flammable; and it should be stable. None of the refrigerants available at that time, including sulphur dioxide, carbon dioxide, ammonia, methyl chloride, and ethyl chloride; could meet any of the requirements. The CFC refrigerants fulfilled all the primary requirements and heralded an unprecedented revolution in the refrigeration and air-conditioning industry (Bhatti, M.S.1999). Today, the litany of the requirements imposed on an ideal refrigerant has increased. The additional primary requirements now include zero Ozone Depletion Potential (ODP) and zero Global Warming Potential (GWP) (Kumar KS, Rajagopal K,
2007 and Park K, Shim Y, Jung D 2009). According to Calm et al. (Calm JM, Wuebbles DJ, Jain AK 1999), the environmental concerns relating to ozone depletion and global warming were not dreamt of when Midgley and associates invented the CFC
refrigerants.
A single-fluid Hydrofluorocarbon (HFC) refrigerant, R134a and R152a are the leading replacement for domestic refrigerators. Although the ODP of these are zero, (Table 1).

Table 1.1: Some properties and environmental impacts of selected alternative refrigerants

Refrigerants

Chemical

formula

Molecular

mass

Boiling point( ºC)

Ozone depletion

potential(ODP)

Global warming

potential (GWP)

R12

CF2 CL2

121

-29.8

1

8100

R125

C2 HFs

120

-48.1

0

2800

R134a

C2 H2 F4

102

-26.1

0

1300

R143a

C2 H3 F4

84

-47.2

0

3800

R152a

C2 H4 F2

66

-24.0

0

140

Sources: ASHRAE, 2001; Bitzer, 2007.
International concern over relatively high global warming potential of R134a has caused some European countries to remove R134a from refrigerator/freezers and abandon it as replacement refrigerant in domestic refrigerator. For this reason, the production and use of R134a will be terminated in
the near future (Bolaji, B.O. 2008 and Wongwises S, Chimres N 2005). Therefore, other replacements will be needed that are thermodynamically attractive as R134a. This paper compares the performance of R134a and other two low GWP HFC refrigerants (R32 and R152a) in vapour compression

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International Journal of Scientific & Engineering Research, Volume 3, Issue 12, December-2012

ISSN 2229-5518

refrigeration system. The performance parameters of the refrigerants were determined by means of theoretical cycle calculation using experimental data.

2. Experimental

2.1 Technical detail of experimental system

The ‘UNICOOL’ make, vapour compression refrigeration system manufactured by NEELAM ENGG., AGRA helps in understanding basics of a refrigerator. A small heater provided in evaporator simulates heat load. Various measurements like evaporating and condensing pressure and temperature, input to compressor and heater enable the students to calculate power consumption and theoretical and actual COP of the refri geration system.
The machine consists of following components:
• Hermitically sealed KIRLOSKAR compressor of capacity 1/3 tons which runs on R12 operating between 0 and 55oC
• Air cooled condenser (Free Convection)
• Evaporator with proper insulation and a variable input heater installed inside
• Capillary expansion valve
• Measuring gauges for temperature and pressure at all control points.

2.2 Objective

The vapour compression refrigeration system is an important refrigeration unit of the thermal lab of the department of mechanical engineering of University institute of technology, the constituent college of the Rajiv Gandhi technical university, which controls engineering education in the state of Madhya Pradesh. The vapour compression refrigeration
system operates on refrigerant R12 which is most important CFC refrigerant identified for phase out in the country by HFC refrigerant. The system is frequently used for experimentation by graduate and post graduate students of the department. The institute has been one of the few institutes selected for funding for research work under World Bank project TEQIP. A research work was undertaken for finding the most suitable ozone-friendly Hydrofluorocarbon refrigerant for replacing ozone depleting refrigerant R12. In the paper, the performance evaluation of alternative ozone-friendly Hydrofluorocarbon refrigerants in the vapour compression refrigeration system has been done. Then most suitable refrigerant has been selected for replacing harmful refrigerant.

2.3 Replacement

Imminent CFC shortages would threaten the useful life of the
appliance of CFC equipment. As the CFC shortages increase,
the cost of CFCs will rise, along with the operating costs of the equipment. “Replacement” is the only term and the most effective solution for discontinuing and reducing the CFC emissions from existing appliances. Replacement is the process by which the equipment currently using an ozone depleting refrigerant is made to operate on a non ozone depleting refrigerant, without major effects on the
performance of the equipment and without significant modifications or changes for the equipment, ensuring that existing equipment operates until the end of it’s economic life. It has been proved by various case studied that retrofitting is economically viable in small scale refrigeration equipment than in large capacity systems.

2.4 Theoretical Analysis and Methodology

A vapour compression refrigeration system is widely used refrigeration method for both domestic and commercial refrigerators. It uses circulating liquid refrigerant as a medium which absorbs heat from the space to be cooled and subsequently rejects that heat elsewhere. Four non-ozone depleting HFC refrigerants (R125, R134a,R143a and R152a) were selected from methane and ethane derivatives and their
performances in vapour compression refrigeration system were investigated. The p-h diagram shown in Fig.1 is frequently used in the analysis of vapour compression refrigeration cycle. The Vapour compression refrigeration system is developed to investigate the effect of the evaporating and condensing temperature on the following performance parameters of the of vapour compression refrigeration system: the refrigerating capacity (RC), the compressor work input (

), the coefficient of performance(COP).The required data for the models are:
Specifying the nature of the refrigerant by fixing the physical and thermodynamic properties obtained from ASHRAE (2001).
Fixing the evaporator and condenser temperatures. Fixing the refrigerant mass flow rate in (kg/s).

Fig 1: Vapour compression refrigeration cycle on p-h diagram The p-h diagram is frequently used in the analysis of vapour compression refrigeration cycle and usually consists of the four processes.
Process 1-2 is the compression. Process 2-4 is the Condensation. Process 4-5 is the expansion. Process 5-1 is the evaporation.

3. Methodology

pvk = c
Where
V = Volume

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International Journal of Scientific & Engineering Research, Volume 3, Issue 12, December-2012

ISSN 2229-5518

C = Constant
K= Polytropic index
p1 v1k = p2 v2 k

k



T2 P2
=
T1 P1

K-1

K

K-1

K

v2

v1

p1
= p2
T = T P2
P1

1



v2 = p1
The polytrophic index (k) is evaluated at T1
CP

v1 p2 k =
From the ideal gas equation
PV=RT

V= RT

P

Cv
T1 and T2 are the suction and discharge temperatures.
P1 and P2 are the evaporating and condensing pressures.
Cp = Specific heat capacit y at constant pressure.
Cv = Specific heat capacit y at constant volume.

V1 = P1 and V2 =

RT2 (4)

P2

Substituting for V1 and V2 in equation (3)

1


RT2P1 = P1 k

The model will estimated at following data :
The compressor discharge T2 and the different enthalpies involved in the cycle.

RT1P2

P1 T2

P2 T1


T2
T1 =

P2

1

P1K

1

P2 K

1


P2 P1 K

1

The compressor work input,
We = mr (h2 - h1)
The heat rejected in the condenser,
Qe = mr (h2 - h1 )
P1 P2 K

-1


K

4. Results and Discussions

T2 P2 P2
= -1
T1 P1 P1 K

1

1-

4.1 Results

The selected Hydro-fluorocarbon (HFC) refrigerants were evaluated at different condensing and evaporating temperature
and the results are as shown below:

T2
T1 =
P2 K

1-1

P1 K
Table 4.1 and 4.2: Thermodynamic properties of refrigerants
at condensing temperature 40ºC
Therefore

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

9.5882

-20

1.5070

60

104.44

31.4

3.3261

R125

20.0790

-20

3.3755

58

68.09

20.76

3.2798

R134a

10.1660

-20

1.3273

60

130.14

40.08

3.2470

R143a

18.3140

-20

3.1535

65

111.87

18.03

6.2047

R152a

9.0927

-20

1.2068

80

221.59

50.49

4.3888

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

9.5882

-10

2.1878

57

109.07

25.7

4.2440

R125

20.0790

-10

4.8272

60

73.25

13.96

5.2471

R134a

10.1660

-10

2.0060

58

136.25

33.41

4.0781

R143a

18.3140

-10

4.4823

56

117.5

18.58

6.3240

R152a

9.0927

-10

1.8152

74

228.8

42.87

5.3370

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International Journal of Scientific & Engineering Research, Volume 3, Issue 12, December-2012

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-20 ºC and Tc of 40ºC.

Draw Chart

250

200

150

100

RC (KJ/kg) We(KJ/kg)


Draw Chart

250

200

150

100

50

RC (KJ/kg) We(KJ/kg) COP

50 COP 0

0

Figure 4.1: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
Figure 4.2: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
-10 ºC and Tc of 40ºC.
Table 4.3 and 4.4: Thermodynamic properties of refrigerants at condensing temperature 30ºC

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

7.4365

-20

1.5070

48

114.61

27.97

4.0976

R125

15.6800

-20

3.3755

46

82.84

24.03

3.4474

R134a

7.7020

-20

1.3273

48

144.83

36.14

4.0075

R143a

14.3400

-20

3.1535

58

129.35

23.4

5.5278

R152a

6.8982

-20

1.2068

64

240.14

48

5.0000

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

7.4365

-10

2.1878

44

119.25

22.04

5.4106

R125

5.6800

-10

4.8272

47

88.00

18.83

4.6734

R134a

7.7020

-10

2.0060

46

150.94

29.26

5.1586

R143a

4.3400

-10

4.4823

56

135.38

17.37

7.7939

R152a

6.8982

-10

1.8152

58

247.34

38.9

6.3500


Draw Chart Draw Chart

300

250

200

150

100

50

0

RC (KJ/kg) We(KJ/kg) COP

Figure 4.3: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
-20 ºC and Tc of 30ºC

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300

250

200

150

100

50

0

RC (KJ/kg) We(KJ/kg) COP

Figure 4.4: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
-10 ºC and Tc of 30ºC

Table 4.5 and 4.6: Thermodynamic properties of refrigerants at condensing temperature 20ºC

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

5.6642

-20

1.5070

34

124.51

23.16

5.3821

R125

12.0500

-20

3.3755

34

96.72

22.88

4.0502

R134a

5.7171

-20

1.3273

36

159.08

31.1

5.1151

R143a

11.0520

-20

3.1535

42

145.89

25.67

5.6832

R152a

5.1291

-20

1.2068

48

258.17

39.33

6.5642

Refrigerants

Pe (bar)

Te (ºC)

Pe(bar)

T2 (ºC)

RC (KJ/kg)

We(KJ/kg)

COP

R12

5.6642

-10

2.1878

31

129.15

17.02

7.588

R125

12.0500

-10

4.8272

34

101.88

18.51

5.838

R134a

5.7171

-10

2.0060

32

165.19

23.12

7.145

R143a

11.0520

-10

4.4823

40

157.52

19.6

7.7306

R152a

5.1291

-10

1.8152

40

266.38

30.13

8.8410


Draw Chart

300

250

200

150

100

50

0

RC (KJ/kg) We(KJ/kg) COP


Draw Chart

300

250

200

150

100

50

0

RC (KJ/kg) We(KJ/kg) COP

Figure 4.5: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
-20 ºC and Tc of 20ºC.
Figure 4.6: The compressor work, refrigerating capacity
and coefficient of performance of the refrigerants at Te of
-10 ºC and Tc of 20º.

4.2 Discussion

Figure 4.1 to 4.6 show the refrigerating capacity of the selected HFC refrigerants and that of R12. The RC increases as the evaporating temperature increases and also
increases as the condensing temperature reduces. R134a, R152a and R143a have a higher refrigerating capacity than that of R12 for the three condensing temperatures considered, while that of R125 is much lower and the

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cooling effect of a vapour compression refrigeration system is evaluated by its refrigerating capacity.
Figure 4.1 to 4.6 show the effect of evaporating temperatures on the compressor loads for the three condensing temperatures (40, 30 and 20°C) for R12 and its potential alternative HFC refrigerants in a vapour compression refrigeration system. As shown in these figures, the compressor work increases as the evaporating temperature reduces and increases as condensing temperature increases.
Figure 4.1 to 4.6 show the variation of coefficient of performance (COP) with varying evaporating temperature for three condensing temperatures (40, 30 and 20°C) for R12and its four HFC refrigerants in a vapour compression refrigeration system. As shown in these figures, COP increases as the evaporating temperature increases and it reduces as the condensing temperature increase. Similar trends and variations were obtained for COP of the potential alternative HFC refrigerants for all the cases studied.R134a andR152a shows a slightly lower and .higher COP with average value of 3.9% an 13.2% and that of R12. An average value of 34% lower and 35.2% higher were obtained for R125 and R143a. At a lower evaporating and condensing temperature, the COP ofR143a reduces.
Based on these results, R152a and R134a are better R12alternatives than R125 and R143a because they have higher refrigerating capacity (RC) and coefficient of performance (COP) which are required in a vapour compression refrigeration system, but R134a which is the current leading alternative for R12 in all domestic applications has a relatively high global warming potential (GWP) and has hindered its general acceptance as the ideal alternative refrigerant (Table 1.1). Therefore R152a with lower GWP is recommended for comprehensive evaluation.

5. CONCLUSION AND RECOMMENDATION

R12 that is commonly used as working fluid in vapour compression refrigeration system all over the world is being phased out due to their environmental hazard of ozone depletion. In this research work, the performance of four HFC refrigerants (R125, R134a, R143a and R152a) regarded as R12 alternative in vapour compression
refrigeration system were investigated using simulation model. The model was developed to predict the performance of the selected refrigerants based on their coefficient of performance (COP), refrigerating capacity (RC) and the compressor work.
The result obtained showed that R152a and R134a have physical properties and thermodynamic performance
similar to R12. R152 has higher coefficient of performance (COP), higher refrigerating capacit y than R12, while R134a has a slightly lower COP and higher refrigerating capacit y than R12. Due to the high global warming potential (GWP) of R134a, R152 will be preferred as working fluid in vapour compression refrigeration system.

REFERENCES

Bhatti, M.S. (1999). A historical look of clorofluorocarbon refrigerants. ASHRAE Transactions, part 1, 1999.pp.1186-
1206
Bolaji, B.O. (2005). CFC refrigerants and stratospheric ozone: past, present and future, In: Environment sustainability and conservation in Nigera, Okoko, E, and Adekunle, V.A.J. (Eds.); Book of reading of Environment conservation and Research Team, chap. 37, pp. 231-239.
Bolaji, B.O. (2008). Investigating the performence of some environment-friendly refrigersants as alternative to R12 in vapour compression refrigeratrion system. PhD. Thesis in the Department of Mechanical Engineering, Federal University of technology, Akure, Nigeria, pp. 150.
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Kumar KS, Rajagopal K, Computational and experimental investigation of low ODP and low GWP HCFC-123 and HC-290 refrigerant mixture alternative to R12, Energy Conversion and Management 48 (2007) 3053-3062.
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