Alternatives to R134a (CF 3 CH 2 F) Refrigerant- A Review

Transcription

1 Alternatives to R134a (CF 3 CH 2 F) Refrigerant- A Review Gaurav a, Dr. Raj Kumar b a Assistant Professor, Department of Mechanical Engineering, Mewat Engineering College, Mewat , Haryana, India. gaurav.citm@gmail.com b Professor, Department of Mechanical Engineering, YMCA University of Science & Technology, Faridabad , Haryana, India Abstract R134a (Hydrofluorocarbon refrigerant) is used in domestic refrigeration and other vapour compression system. R134a is having zero ozone depletion potential (ODP) and almost same thermodynamic properties as R12 (Chloroflurocarbon refrigerant), but it has 1300 global warming potential (GWP) per year which is very high. So, there is a need to find out the alternatives to R134a from toxicity, flammability, thermodynamic, thermoeconomic and environment point of view. This review paper also represents the recent development done on alternatives to R134a. Keywords: Global warming, Ozone depletion, Alternative refrigerant, Flammability 1. Introduction The first mechanically produced cooling system was developed in England in The process later became known as vapour compression. After availability of electricity automatic refrigeration system was developed in Basically a refrigeration or air conditioning is nothing more than a heat pump whose job is to remove heat from a lower temperature source and reject heat to high temperature sink. Figure 1 The vapour compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Figure 1 depicts a typical, single-stage vapour-compression system. All such systems have four components: a compressor, a condenser, a thermal expansion valve (also called a throttle valve or Tx Valve), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapour and is compressed to a higher pressure, resulting in a higher temperature as well. Saturated vapour is then routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried 73

2 away by either the water or the air (whichever may be the case). The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapour refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated. The cold mixture is then routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapour mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The refrigerant vapour from the evaporator is again a saturated vapour and is routed back into the compressor, thus cycle repeats. 2. Literature Review: R. Cabello et al [1] studied the influence of the evaporating pressure, condensing pressure and superheating degree of the vapour on the exergetic performance of a refrigeration plant using three different working fluids R134a, R407c, R22. K. Senthil Kumar et al [2] studied the behavior of HCFC (Hydrochloroflurocarbon) -123/ HC-290 refrigerant mixture computationally as well as experimentally and found that refrigerant mixture 7/3 as a promising alternative to R12 system. B.O. Bolaji et al [3] investigated experimentally the performances of three ozone friendly Hydrofluorocarbon refrigerants R12, R152a and R134a. R152a refrigerant found as a drop in replacement for R134a in vapour compression system. B.O. Bolaji [4] discussed the process of selecting environmental-friendly refrigerants that have zero ozone depletion potential and low global warming potential. R23 and R32 from methane derivatives and R152a, R143a, R134a and R125 from ethane derivatives are the emerging refrigerants that are non toxic, have low flammability and environmental-friendly. These refrigerants need theoretical and experimental analysis to investigate their performance in the system. A.S. Dalkilic et al [5] studied the performance analysis of alternative new refrigerant mixtures as substitute for R12, R134a and R 22. Refrigerant blend of R290/R 600a (40/60 by wt. %) and R 290/R1270 (20/80 by wt. %) are found to be the most suitable alternative among refrigerants tested for R12 and R22. S. Wongwises et al [6] found that 6/4 mixture of R290 and R600 is the most appropriate refrigerant to replace HFC134a in a domestic refrigerator. K Mani et al [7] found that R290/R600a (68/32 by wt. %) can be considered as a drop in replacement for R12 and R134a. Miguel Padilla et al [8] found that R413A (mixture of 88% R134a, 9%R218, 3%R600a) can replace R12 and R134a in domestic refrigerator. Bukola O. Balaji et al [9] investigated the exergetic performance of R12 and its substitute (R134a and R 152a) in the domestic refrigerator. R152a performed better than R134a in terms of COP, exergetic efficiency and efficiency defect as R12 substitute in domestic refrigeration system. Alka Bani Agrawal et al (10) worked on eco-friendly refrigerant as a substitute for CFC (Chloroflurocarbon). The binary mixture in the ration of 64% and 36% of R290 and R600a found to be a retrofit or drop in substitute of R12 for use in the vapour compression refrigeration trainer. M.M. EI-Awad [11] performed the validation of model against experimental data that compared the performance of liquefied petroleum gas (LPG) to that of refrigerant R12 for domestic refrigeration. Abhishek Tiwari et al [12] published a review paper on recent development on domestic refrigeration. 74

3 3. Need for Alternatives of R134a 3.1 Generation of Refrigerants: The first generation ( ) of refrigerants was based on the availability. These refrigerants were often highly toxic, flammable and some very highly reactive. Example Ethers, CO 2, NH 3, CCl 4 etc. The second generation ( ) of refrigerants focused on reducing toxicity and flammability. Example: CFCs, HCFCs, HFCs, NH 3, H 2 O etc. The third generation ( ) of refrigerants focused on protecting the ozone layer. Example - HCFCs, HFCs, HCs, NH 3, H 2 O, CO 2 etc. The fourth generation (from 2010 onwards) focused on refrigerants that do not contribute to global warming, ozone layer depletion, efficient, non flammable and non toxic with good stability. But the outlook for discovery or synthesis of these ideal refrigerants is extremely unlikely. Therefore, trade -off among desired objectives are necessary to achieve the balanced solution. 3.2 Montreal Protocol: In 1987 Montreal protocol established the requirements that began the world wide phase out of CFCs. Production of CFCs was phased out by the Montreal Protocol in developed countries in 1 st of January, Production in developing countries was phased out in 2010 [4]. In 1992 Montreal protocol established the requirements that began the world wide phase out of HCFCs. Complete production of HCFCs will be phased out by Montreal protocol in Kyoto Protocol: Kyoto protocol aims at phasing out of substances that will lead to global warming. R134a is used in domestic refrigerator and other vapour compression systems as it was identified as a replacement to CFC-12, keeping in view its zero ozone depleting potential. R134a has 1300 global warming potential per 100 year, which is very high. The sale of R134a reported to AFEAS [13] is significantly increasing during the past two decades. The increased emission of R134a to the atmosphere are steadily increasing the concentration of green house gases via leaks and mostly, in an indirect way, via energetic performance of refrigeration plant. This will lead to adverse climatic problem. Hence, R134a is one of the six chemicals in the basket that are to be phased out in the near future under Kyoto protocol. 4. Environmental Concern The first major concern is depletion of ozone layer. Ozone layer is a layer which protects the earth from ultraviolet rays. Ozone depletion potential is evaluated on a scale that uses CFC-11 as a benchmark. All the other components are based on how damaging to the ozone they are in relation to CFC-11. The second major concern is global warming. Global warming is the increase in global earth surface temperature due to the absorption of infrared emission from earth surface. Global warming potential is evaluated on a scale that uses CO 2 as the bench mark i.e. CO 2 is assigned a value and other components are compared to CO Analysis of Vapour Compression Refrigeration Cycle Thermodynamic analysis is the analysis based on energy. Raising the efficiency of an energy system is within the domain of thermodynamics. Thermoeconomic analysis is the analysis based on exergy and economic principles to provide system designer or operator with information not available through conventional energy analysis and economic evaluations but crucial to the design and operation of a cost effective system. Energy cannot be destroyed-a first-law concept. The idea that something can be destroyed is useful in the design and 75

4 analysis of thermal systems. This idea does not apply to energy, however, but to exergy (availability)-a second law concept. Exergy analysis usually predicts the thermodynamic performance and the inefficiency of an energy system. 6. Alternatives to R134a Chlorine content present in the CFCs and HCFCs contribute to depletion of ozone layer. Hence, Montreal Protocol established the phase out of CFCs and HCFCs. Alternative refrigerant of CFCs and HCFCs is HFCs as there is no chlorine content in it. R134a is HFC (Hydrofluorocarbon) refrigerant. Through research it was found that R134a contribute to Global Warming because of Fluorine content in it. R134a has a relatively high global warming potential (1300 times that of CO 2 ). Although Global warming is a good thing in itself and allows life to exist in all its variety but the concern is that man s activities are increasing the concentration of carbon dioxide and other green gases in the atmosphere, causing the amount of absorbed infrared radiation to increase, and leading to atmospheric temperatures and consequent long term climate changes. Hence, Kyoto protocol established the phased out of HFCs in the near future. Montreal and Kyoto protocols are interconnected, total climate change and ozone depletion depends on both the global warming potential and ozone depletion potential of the substances [14]. Alternative to HFC refrigerants can be HC (Hydrocarbon) as there is no fluorine content. Hydrocarbons (HCs) are the class of natural occurring substances that include propane, pentane and butane. HCs are excellent refrigerants in many ways - energy efficiency, critical point, solubility, transport, heat transfer properties and environmentally sound but their major concern is their flammability. Properties of alternative refrigerants of R134a are given in Table 1. Refrigerant (Category) Chemical Formula Normal Boiling Point ( C) Table 1 Critical Temperature ( C) ODP GWP (per 100 Year) Safety Group R134a CF 3 CH 2 F A1 R152a CH 3 CHF A2 R290 (HC) C 3 H A3 R600 (HC) C 4 H R600a (HC) (CH 3 ) 3 CH A3 R32 CH 2 F A2 R143a CH 3 CF A2 R125 CHF 2 CF A1 R123 (HCFC) CHCl 2 CF B1 Comparing the different values of alternative refrigerants as given in above table and from literature review, some of the alternative refrigerants of R134a can be R32, R152a, R125, R413A (mixture of 88% R134a, 9%R218, 3%R600a), R290/R600a (68/32 by wt. %), R290/R 600a (40/60 by wt. %) and R123/ R290 (mixture of 7/3). These alternative refrigerants must be compare thermodynamically and thermoeconomically (Exergy +Economic), so that best alternative can be found out. 76

5 7. Conclusions Following conclusions can be drawn from this review paper R134a is a HFC refrigerant and it contributes to global warming because of fluorine content in it. Ozone depletion and total climate change depends on both global warming potential and ozone depletion potential. So, there is a need to find out alternatives of R134a under Kyoto protocol and Montreal protocol. From literature review and properties of refrigerant R32, R152a, R125, R413A (mixture of 88% R134a, 9%R218, 3%R600a), R290/R600a (68/32 by wt. %), R290/R 600a (40/60 by wt. %) and R123/ R290 (mixture of 7/3) are identified as alternatives of R134a. There is a need of comparing the alternative refrigerants from thermodynamic, thermoeconomical, environmental, toxicity, stability and flammability point of view. So, that best alternative to R134a can be found out. There is a need of further research to be done on the different mixtures of HFCs and HCs, to find the alternatives of R134a. References [1] R. Cabello, E. Torrella, J. Navarro-Esbri, Experimental evaluation of a vapour compression plant performance using R134a, RR407C and R22 as working fluids, Applied Thermal Engineering 24 (2004) [2] K. Senthil Kumar, K. Rajagopal, Computational and experimental investigation of low ODP and low GWP HCFC-123 and HC-290 refrigerant mixture alternative to CFC-12, Energy Conversion and Management 48 (2007) [3] B.O.Bolaji, M.A. Akintunde, T.O. Falade, Comparative analysis of performance of three ozone-friends HFC refrigerants in a vapour compression refrigerator, Journal of Sustainable Energy and Environment 2 (2011) [4] 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) [5] A.S. Dalkilic, S. Wongwises, A performance of vapour-compression refrigeration system using various alternative refrigerants, International Communication in Heat and Mass Transfer 37 (2010) [6] Somchai Wongwises, Nares Chimres, Experimental study of hydrocarbon mixtures to replace HFC-134a in a domestic refrigerator, Energy Conversion and Management 46 (2005) [7] K. Mani, V. Selladurai, Experimental analysis of a new refrigerant mixture as a drop in replacement for CFC 12 and HFC 134a, International Journal of Thermal Science 47 (2008) [8] Miguel Padilla, Remi Revellin, Jocelyn Bonjour, Exergy analysis of R413A as a replacement of R12 in a domestic refrigeration system, Energy Conversion and Management 51 (2010) [9] Bukola o. Bolaji, Exergetic performance of a domestic refrigerator using R12 and its alternative refrigerants, Journal of Engineering Science and Technology, Vol. 5, No. 4 (2010) [10] Alka Bani Agrawal and Vipin Shrivastava, Retrofitting of vapour compression refrigeration trainer by an ec0-friendly refrigerant, Indian Journal of Science and Technology, Vol. 3, No. 4 (2010) [11] M.M. EI-Awad, Validation of computerized analytical model for evaluating natural hydrocarbon mixtures as alternative refrigerants, Journal of Sustainable Energy and Environment 2 (2011) [12] Abhishek Tiwari, R.C. Gupta, Recent developments on domestic refrigerator-a review, International Journal of Engineering Science and Technology, Vol. 3, No. 5(2011) [13] <http;// [14] Report of the TEAP HFC and PFC Task Force, The implication to the Montreal protocol of the inclusion of HFCs and PFCs in the Kyoto Protocol: October [15] C.P.Arora, Refrigeration and Air Conditioning, Tata MeGraw Hill, New Delhi, India,