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A REVIEW ON LPG AS A REFRIGERENT Mr. Shubham P. Duddalwar1, Mr. Anup S. Batki2, Mr. Ritesh A. Wawre3 , Prof. A. B. Samarth4 1

B.E. Scholar, Department of Mechanical Engineering,Jagadambha College of Engineering & Technology, Yavatmal ,Maharashtra, India, [email protected] 2 B.E. Scholar, Department of Mechanical Engineering,Jagadambha College of Engineering & Technology, Yavatmal ,Maharashtra, India, [email protected] 3 B.E. Scholar, Department of Mechanical Engineering,Jagadambha College of Engineering & Technology, Yavatmal ,Maharashtra, India, [email protected] 4 Asst. Professor, Department of Mechanical Engineering, Jagadambha College of Engineering & Technology, Yavatmal ,Maharashtra, India, [email protected] ABSTRACT Currently manufactured Indian refrigerators mainly use the conventional CFC’s, namely CFC-12 as refrigerant. However, the selection of alternative refrigerants is still being debated. There is a need to assess various refrigerant options considering the existing refrigerators in the field and for the future market. This paper addresses the issues related to the use of LPG as a refrigerant, in Indian refrigerators, including retrofitting performance, field usage and servicing. CFC,s are principally destroyed by ultraviolet radiations in the stratosphere; the chlorine released in the high stratosphere catalyzes the decomposition of ozone to oxygen; and ultraviolet radiation penetrates to lower altitudes. Credible calculations of the magnitude of this effect (Hoffman 1987) and his team predicted 3% global ozone depletion for constant CFC emissions of 700 thousand tonnes /year after a hundred years. The ozone impact of car air conditioners also cannot be ignored. A car air conditioner may lose 400g/year of dichlorodifluoromethane (R12) through hoses, pipe joints and shaft seals. Considering future population, if R-12 were still used, cars would emit 800 thousand tonnes/year and fridges 20,000 tonnes/year. Hydro fluorocarbons (HFC’s) can be thought of as a replacement, but unfortunately the radiation properties of HFC’s like R-134a make them powerful global warming agents. Thus, hydrocarbon refrigerants; particularly LPG serves as the best contender to replace CFC's from domestic refrigerators as well as car air conditioners. LPG (Liquefied petroleum gas) consists mainly of propane (R-290) and butane (R-600), and LPG is available as a side product in local refineries. In Cuba for already several decades LPG is used as a drop-in refrigerant. LPG mixtures have composition of a commercial LPG mixture suitable as ‘drop-in’ replacement for R-12 was calculated crudely as 64% propane and 36% butane by mass.

Keywords: Heat Transfer1, Cylindrical perforated Fins2, Staggered Arrangement3, Inline Arrangement4. ----------------------------------------------------------------------------------------------------------------------------1. INTRODUCTION Liquid Petroleum Gas (LPG or LP Gas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing fluorocarbons as a refrigerant to reduce damage to the ozone layer. The gases are a mix of propane and butane usually with propylene and butylenes present in small concentration. A powerful oderant, ethyl mercaptan, is added to these so that leaks can be detected easily. LPG is manufactured during the refining crude oil, or extracted from oil or gas streams as they emerge from the ground. It becomes liquid at room temperature under pressure, so is supplied in pressurized steel bottles. These are usually filled to 85% of their capacity with the liquified gas to provide room for the liquid to expand if the bottle gets hot. The liquified gas has an expansion ratio of about 250:1. It has density almost twice as that of air. LPG was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912 It currently provides about 3% of the energy consumed in the United states. In November of last year the British Standard BS4434 was changed to widen the use of LPG refrigerants, not just for domestic use but also for commercial and industrial purposes. This opened up new horizons for the use of LPG refrigerants in many applications. The standard breaks down locations into 3 categories. The first category covers public areas. The charge size is limited to 1.5 kgs per sealed system and not exceeding 5 kg in special machinery rooms for indirect systems. The second category is for: IJRISE| www.ijrise.org|[email protected] [115-121]

International Journal of Research In Science & Engineering Volume: 2 Special Issue: 1-ICRITE

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small shops, offices, general manufacturing and work places. Here the charge size must not exceed 2.5 kg per sealed system and 10 kg in special machinery rooms, again for indirect systems. The third and last category covers industrial applications, cold stores and non public areas. The charge must not exceed 10 kg in humanly occupied space- 25 kg for systems with high pressure in a special machinery room.

2. LITERATURE SURVEY B.O. Bolaji [1] discussed the process of selecting environmental-friendly refrigerants that have zero ozone depletion and low global warming potential. The refrigerants R23 and R32 from methane family and R152a, R143a, R134a and R125 from ethane family are non toxic, having low flammability and are eco-friendly. To investigate their performance in the system theoretical and experimental analysis are needed. Eric Granryd [2] gave the list of the different hydrocarbons as working medium in refrigeration system. He showed the properties of hydrocarbons that make the refrigerating alternatives for energy efficient and ecofriendly. He studied the different safety standards related to these refrigerants. Due to flammability, safety precaution should be taken. Mao-Gang He, Tie-Chen Li, Zhi-Gang Liu and Ying Zhang [3] analyzed that the mixture of R152a/R125 in the composition of 0.85 mass fraction of R152a has a similar refrigeration performance with the existing refrigerant R12.Experimental research on the main refrigeration performances of domestic refrigerators was conducted, under the different proportions and charge amounts, when R152a/R125 is used to substitute R12 as a drop-in refrigerant. The experimental results indicate that R152a/R125 can be used to replace R12 as a new generation refrigerant of domestic refrigerators, because of its well environmentally acceptable properties and its favorable refrigeration performances. R.W.James & J.F.Missenden [4] examined the use of propane in domestic refrigerators and conclude that he implications of using propane in domestic refrigerators in relation to energy consumption compressor lubrication, costs, availability, environmental factors and safety propane is an attractive and environmentally friendly alternative to CFCs used currently. Ju Hyok Kim,Jin Min Cho, Min Soo Kim [5], have worked on cooling performance of several CO2 or propane mixtures and glide matching with secondary heat transfer fluid. It shows that CO2 or propane mixtures are the possibility in keeping the highest pressure of the system below a limit by selecting the composition. The discharge pressure of CO2 or propane mixtures is reduced with increasing mole fraction of propane and their reduced values coincide approximately with the circulation concentrations of propane. Propane is the refrigerant having a higher refrigerating effect and a much lower vapour density than CO2, adding propane to CO2 improves the efficiency and reduces the cooling capacity. M. Rasti ,M.S. Hatamipour, S.F. Aghamiri, M. Tavakoli [6] investigated on enhancement of domestic refrigerator’s energy efficiency index using a hydrocarbon mixture refrigerant and sowed that R436A in a 238 L single evaporator domestic refrigerator without any modification in refrigeration cycle. The refrigerator’s compressor was charged with different amount of R436A.In comparison with R134a, the charge amount of R436A is reduced by 48%; the ON time ratio is reduced by 13%; the energy consumption is reduced by 5.3% in 24 h; the evaporator inlet temperature is reduced by 3.5 C; The results showed that TEWI of R436A is 11.8% less than R134a.According to our results and known environmental effects,R436A appears to be a suitable replacement for R134a A.Baskaran, and P.Koshy Mathews [7] analysed the performance on a vapour compression refrigeration system with various eco-friendly refrigerants of HFC152a, HFC32, HC290, HC1270, HC600a and RE170. They were compared with R134a and the result showed that this refrigerant investigated in the analysis RE170, R152a and R600a have a slightly higher performance coefficient and their results were compared with R134a as possible alternative refrigerant. The evaporating temperatures between -30⁰C and 10⁰C refrigerant RE170 instead of R134a was found to be a replacement refrigerant among other alternatives. James M. Calm [8] has studied the emission and environmental impacts of R11, R123, R134a due to leakage from centrifugal chiller system. He also investigated the total impact in form of TEWI and change in system efficiency or performance due to charge loss. He also summarized the methods to reduce the refrigerant losses by

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the system like design modifications, improvement in preventive maintenance techniques, use of purge system for refrigerant vapour recovery, servicing and lubricant changing in system.

3. NEED FOR REPLACEMENT OF CFC’S:The CFC compound was first synthesized about 70 years ago, and entered commercial use soon afterwards as a refrigerant. The yearly production rose tremendously after the 1950’s and reached the level of 30,000 tones per year in mid 1960’s.CFC’S are transparent, insoluble and non-toxic. But the molecules released to the atmosphere are principally destroyed by the ultraviolet radiation in the stratosphere. The chlorine released in the high stratosphere acts as a catalyst in decomposing ozone to oxygen. Hoffman (1987) predicted 3% global ozone depletion for constant CFC emissions of 700 thousand tones/year after a hundred years. Therefore, the manufacture and import of CFC’S has now ceased in advanced countries. The radiation properties of carbon –dioxide are known to increase the earth temperature. The radiation properties of CFC’S and their long atmospheric lifetimes make them thousands of times worse than carbon dioxide. The solar ultraviolet radiation destroys the CFC molecule as CCL3 + UV  CL + CCL2F This reaction releases the CL atom which affects environmental ozone as CL +03  CLO +O2 This reaction is followed by CLO +O  CL + O2 which regenerates CL atoms and a long chain process is involved. Thus the ozone depletion takes place. Therefore it is imperative that we replace CFC's with some suitable hydrocarbon refrigerants such as LPG in the near future to avoid the ozone depletion for the coming generations. LPG being devoid of chlorine has no chance of undergoing the above mentioned reactions and thus it can be termed as one of the most Eco- friendly alternative for the replacement of CFC’s from international market.

4. ALTERNATIVES TO CFC’s. There is a tremendous effort to develop CFC alternatives all around the world. Any alternative has to posses the desired characteristics. In addition there are other environmental acceptability factors such as zero ozone depletion potential , relatively low global warming potential .The earlier quests for alternatives to CFC’s included some HCFC’s. After the inclusion of HCFC’s under the Montreal protocol, some countries have even volunteered to phase out HCFC’s much earlier than the stipulation of the Montreal protocol. Therefore, it may not be prudent for the developing countries to adopt the emerging technologies using HCFC’s as the technology is likely to become obsolete too soon. However, HCFC’s may be considered wherever they can be used to quickly phase out CFC’s without significant change in investment. Most of the alternatives are merging from HFC family, either as a single or as blends. There is still some uncertainty on their long term usage of HFC’s with respect to the green house effect. In the Kyoto Protocol proposed in December 1997, there are some proposals on the regulation of green house gases including HFC’s .Some countries like Europe and Cuba have given special consideration for the use of natural refrigerants like the hydrocarbons. There is a growing concern about the relatively high GWP of HFCs and HCFCs, and also generally about synthetic fluids as alternatives to CFCs, particularly in Europe. Hydrocarbons are clear from both the environmental issues, viz., the ozone layer depletion and global warming. Initially there were an innate conservatism and apprehension about the use of hydrocarbons in refrigerators. However, with a careful analysis of the various risks and identification of appropriate mitigation strategies, it has been proved that the risks can be managed. This is exemplified by the fact that German refrigerator industry would soon convert completely to hydrocarbons, namely, HC-600a and cyclopentane.

4. WHY LPG? Refrigerant Class Ozone depletion potential Global warming potential

R-12 CFC 1.0 7300

R-22 HCFC 0.07 1500

R-134a HFC 0 1200

Table 1: Environmental impacts of refrigerants (100 year basis).

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R600a LPG 0 8

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The table shows that the LPG refrigerant (R-600a) has zero ozone depletion potential and a near zero global warming potential . The above values combined with some of the other properties of LPG refrigerants makes them an obvious choice as a refrigerant in future refrigeration. In fact, countries like Europe and Cuba are already using hydrocarbon refrigerants in their refrigerators since 1993 and have found no trouble whatsoever using them. Translating Table 1 to dollars and cents may help us appreciate the significance of CFC and HFC GWP’s. An Australian proposal for a tax on emitted carbon dioxide of 1.25 $/tonne was abandoned in January 1994. Partly because a tax which adds only 0.2 cents/kW hr to the price of coal fired electricity would not significantly reduce CO2 emissions. If the global warming contribution of R-134a was taxed at the same rate it would be 1.5$/kg R-134a which gives R-600a a 3.67$/kg price advantage. Some governments may do more than tax R-134a to meet their treaty commitments (Tickell et al. 1995). Code R-290 R-600a R-600

Chemical name Propane Iso-butane Normal butane

Triple (°C) -189 -145 -138

Boil (°C) -42.08 -11.76 -0.54

Critical (°C) 96.70 134.70 152.01

Table 2 : LPG refrigerants used for domestic and light commercial applications Acceptable performance and life for refrigerants in domestic and light commercial use requires they be noncorrosive, chemically stable, boil below ambient temperatures and have a critical temperature above ambient. Table 2 shows naturally occurring hydrocarbons and mixtures which satisfy these criteria. They are called LPG refrigerants here.

5. PERFORMANCE OF LPG REFRIGERANTS. Make

Model

Refrigerant

UK UK Liebherr Siemens

A B KT1580 KT15RSO

R-12 R-12 R600a (LPG) R600a (LPG)

Capacity (L) 129 160 155 144

Consumption (KWhr/24 hr) 0.75 0.71 0.38 0.52

Table 3 : Energy consumption of domestic refrigerators to ISO 7371 with internal temperature 5°C and ambient 25°C. The table above shows the superiority of LPG as a refrigerant. It shows that the energy consumption of the LPG refrigerators is round about 60% to that of the refrigerators using R-12 as the refrigerant. In February 1995, Email released the first of its R600a refrigerators with a 16% energy saving over the previous R134a models. Abound (1994) measured the refrigerant charge, suction superheat, condenser pressure and relative cooling capacity on the air conditioners of five popular Australian cars.R-12 was compared with mixtures of commercial propane and butane. The measurements were made on the cars at idle. The relative cooling capacity of the LPG mixture to R-12 was calculated from the return and supply air states in the passenger compartment and from the compressor speed, pressures and temperatures in the refrigerant circuit. The measures of the ratio of LPG to R-12 capacity disagreed sometimes by 20 %. A 60 % propane and 40% butane mixture by mass was measured to increase the cooling capacity by typically 10% over R-12. The measurements indicated reduced compressor work but this could not be determined accurately. The superheats measured were satisfactory with typically an 8% increase in the condenser pressure. The overall weight of the system also is reduced as the density of LPG is much higher than that of R-12. The overall efficiency of the system also is improved by 10-20% by using LPG as a refrigerant.

5. COMPARISION OF REFRIGERANT PERFORMANCE Table 4 : Comparison of refrigerant properties and parameters affecting the measured energy consumption of domestic refrigerators for an idealized reversed Rankine cycle operating between -15°C and 30°C saturation temperatures. The atmospheric pressure is 101.3 kPa.

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Chemical classification Refrigerant Refrigerating effect (J/g) Condenser pressure ( kPa) Evaporator pressure (kPa) Condenser gauge (kPa) Effective displacement (L/Kj) Heat transfer conductance k/µ (Kj/kgK) Compressor discharge temperature (ºC) Liquid molar volume (Ml/mol) COP 0 K suction superheat COP 20 K suction superheat

CFC R-12 116.9 743.2 181.9 641.9 0.79 0.278 39.3 93.5 4.69 4.71

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HFC R-134a 150.7 770.7 163.6 669.4 0.81 0.293 36.6 86.1 4.62 4.71

LPG R-600a 262.3 403.6 89.2 302.3 1.52 0.496 30.0 106.7 4.69 4.82

The large COP improvements in refrigerators using LPG are consistent with their properties. Table 2 compares refrigerant properties ( Gallagher et al. 1993 ) and parameters affecting COP for domestic refrigerators. Saturated vapour at -15ºC is assumed to enter an ideal compressor and saturated liquid at 30ºC to enter the expansion valve except for calculating COP with 20 K suction superheat. Table 2 includes the three refrigerants currently in mass produced domestic refrigerators . Table 2 shows LPG has one irrelevant disadvantage and many significant advantages for domestic refrigerators discussed in the following :1) When R-12 was introduced, open-drive compressors were common and LPG’s below atmospheric evaporator would cause ingress of air through the shaft seals reducing reliability. Domestic refrigerators no longer use open- drive compressors. 2) The condenser gauge pressures for LPG are less than half those for the other refrigerants, so many metal thicknesses can be halved. This reduces capital cost and environmental impacts and increases COP through reduced heat transfer resistance. 3) The COP calculated for a simple reversed Rankine cycle (Figure 1 ) with zero subcooling of liquid and superheat of suction vapour and ideal heat transfer and compression is 1% higher for LPG than R134a. 4) Domestic refrigerators use a capillary tube in close thermal contact with the compressor suction line instead of an expansion valve. With 20 K superheat LPG refrigerants have an idealized COP only 2% higher than R134a. 5) The low compressor discharge temperature for LPG refrigerants allows a cheaper and more efficient design of electric motor. 6) The large effective displacement of LPG refrigerants implies a larger compressor but because condenser gauge pressures are half, compressor wall thicknesses can be halved. An overall reduction in compressor mass and hence capital cost is possible. The compressor will still be much smaller than the driving electric motor. The surface finish of the piston and valves will be the same for LPG and R-134a. Because the LPG compressor is bigger the relative roughness will be smaller allowing an LPG compressor to be more efficient. 7) The usual correlations for this heat transfer (ASHRAE 1993 ) depend mainly on the ratio of the thermal conductivity of the liquid to its dynamic viscosity, k/µ. Hence heat transfer conductance is greater for LPG. A high heat transfer conductance means a smaller COP loss due to heat transfer resistance. 8) Liquid molar volume is related to the size of the molecule. A large molecule means a lower loss rate and a longer period of operation with high COP. In the absence of measurements, R600a’s larger molecule suggests it will have lower diffusion loss. These advantages make LPG desirable in other applications where evaporator or condenser temperatures are high e.g., transport air conditioning and domestic water heat pumps. RC-270 can be a better replacement for R12 and R-134a but if the equipment must be redesigned to minimize GWP, R-600a will give a better result. Ammonia R-717 has higher heat transfer than all these but its vapour pressure, corrosion and toxicity are higher. The toxicity is especially a disadvantage in the domestic applications.

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6. THE EXPLOSION RISK

LPG Refrigerants R-290 R-600a R-600 P-50

Molecular mass g/mol 44.1 58.1 58.1 50.1

Flammability limits. Vol % 2.1 to 11.4 1.9 to 10.0 1.7 to 10.3 2.0 to 10.8

Table 5 : Fire and explosion data for LPG refrigerants at 25°C From the above table we can observe that the average flammability limit for LPG refrigerants is round about 2.0%. If the concentration of the refrigerant goes beyond 2.0% by volume, there is a danger of explosion. Let us consider a 300 liter capacity refrigerator kept in a typically small kitchen of volume 8 m³. The charge equivalent to 300 L capacity refrigerator is 70 gms. Let us calculate the possibilities of explosion in this kind of situation. Now, the density of LPG at room temperature and pressure is approximately 2.1 kg/m³. To be on the safer side let us consider a worst case scenario where the entire refrigerant in the refrigerator is leaked. If the refrigerant is evenly dispersed in the room, then the volume occupied by 70 gm of the refrigerant will be = 0.07kg x 1 m³/ 2.1 kg = 0.033 m³. Therefore, the concentration of the refrigerant in the kitchen by volume % will be = 0.033/8 = 0.0041. Thus the % concentration of LPG in the room will be equal to 0.0041 x 100 = 0.41 % which is way below the maximum flammability limit i.e.2.0%. Thus the weight of LPG in the room required to reach the lower flammability limit will be = 0.07 x (2.0 / 0.41)  340gms. This shows that there is no chance of explosion in this situation and the LPG refrigerant can be safely used without any danger of explosion whatsoever because the refrigerator is working under a safety margin of 340 / 70 = 4.85. Thus, the suggested maximum charge will be 70 gms for a room size of 2m x 2m x 2m. Similarly, the suggested maximum charge for a room size of 3m x 3m x 3m will be around 200 gms, whereas the weight of LPG to reach the lower flammability limit will be equal to 1.1 kg. The above data can be represented in tabular form as: Table 6 : Room size Room volume Weight of Suggested (m³) LPG maximum charge to reach LFL. 2m x 2m x 2m 8 340 g 70 g 3m x 3m x 3m 27 1.1 kg 200 g

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If the refrigerant is evenly dispersed in a typically small kitchen of 8m3, then the amount of refrigerant must be below 340 gms to prevent potential combustion. To provide a high safety margin and to be prepared for the case that the refrigerant may not be evenly dispersed, the charge quantity may be restricted to 70 gms. This is equivalent to the charge in a 300 litre capacity refrigerator. For a bigger kitchen of 27m3, the suggested maximum charge is 200 g and this charge covers the entire range of refrigerators currently made in India. Refrigerators with hydrocarbons have been produced, sold and used in Europe. Since 1993 without any reported accident. Furthermore, a risk assessment showed that the explosion pressure would be low and of short duration, therefore no immediate harm to people is expected. Many other similar tests have been apparently carried out by other manufacturers but their results are not available in public domain. Any enterprise having an intention of manufacturing hydrocarbon refrigerators should first make a preliminary risk assessment. In order to identify some of the critical issues, including safety, for hydrocarbon refrigerators, one has to have some awareness and appreciation of the existing national and international standards for refrigerators and compressors.

7. CONCLUSION Thus, the LPG refrigerants have all the ingredients in them to replace or phase out CFC’s from the current scenario. Developing countries like India are apprehensive of using hydrocarbons as refrigerants. Whereas, countries like Europe and Cuba are already using hydrocarbons like LPG as refrigerants in household as well as industrial applications and are already seeking the benefits. It is about time for tropical countries like ours to realize the importance of reducing the rates of global warming and ozone depletion and make the planet Earth a better place to live in. Steps should be taken in the right earnest, to secure the future for many generations to come. Customers will demand LPG refrigerators because they occur naturally, cause no ozone depletion and negligible global warming. LPG mixtures should replace R-12 and R-134a. The market for R-600a will grow as new equipment exploits the advantages of its appropriate properties. LPG refrigerants have superior properties often giving 10 to 20 % energy savings. They are highly flammable so for charges above 2.5 kg systems should comply with AS 1596-1989. REFERENCES [1] B.O.Bolaji, Selection of environment-friendly refrigerants and the current alternatives in vapour compression refrigeration systems, Journal of Science and Management, Vol 1, No. 1 (2011) 22-26. [2] Eric Granryd, ―Hydrocarbons as refrigerants - an overview, International Journal of Refrigeration 24, pp. 1524, 2001. [3] Mao-Gang He, Tie-Chen Li, Zhi-Gang Liu, and Ying Zhang, ―Testing of the mixing refrigerants HFC152a/HFC125 in domestic refrigerator,‖ Applied Thermal Engineering 25, pp. 1169–1181, 2005 [4]R. W. James and J. F. Missenden-The use of propane in domestic refrigerators ,Institute of Environmental Engineering, Borough Road, South Bank Polytechnic, London,SE1 0AA, UK, Received 10 July 1990; revised 8 October 1991 [5] Man-Hoe Kim, Byung-Han Lim , Euy-Sung Chu, ―The performance analysis of a hydrocarbon refrigerant R600a in a household refrigerator/freezer‖, Journal of Mechanical Science and Technology, Volume 12, Number 4 / July, 2008, pages 753-760. [6] M. Rasti a, M.S. Hatamipour a,⇑, S.F. Aghamiri a, M. Tavakoli b. a Chem. Eng. Dept., University of Isfahan, Isfahan, Islamic Republic of Iran bR&D Dept., Entekhab Industrial Group, Isfahan, Islamic Republic of Iran. [7] A.Baskaran & P.Koshy Mathews, A Performance Comparison of Vapour Compression Refrigeration System Using Eco Friendly Refrigerants of Low Global Warming Potentia . International Journal of Scientific and Research Publications. [8] James M. Calm, ―Emissions and environmental impacts from air-conditioning and refrigeration systems, International Journal of Refrigeration 25, pp. 293–305, 2002. [9] Maclaine-cross .I.L.,1993,”Hydrocarbon Refrigerants and Motor Car Air Conditioning”,22nd November, Paper presented at Green Fridge Quest, Master Class Workshop, National Science and Technology Centre, Canberra. [10] James,R.W.,and Missenden,J.F.,1992;”The use of propane in domestic refrigerators”, International Journal of refrigeration, Vol 15, No. 2 , pp. 95-100. [11] Kuijpers , L.J.M., de Wit , J.A. , Janssen , M.J.P . , 1988 , ” Possibilities for the replacement of CFC12 in Domestic Equipment, International journal of Refrigeration, Vol.11,July, pp. 284-291.

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