Comparative assessment for drop in replacement of R134a in domestic refrigerator.

Comparative assessment for drop in replacement of R134a in domestic refrigerator. Pravin K. Katare Research Scholar, Department of Mechanical Engineering, G.H.Raisoni College of Engineering Digdoh Hill, Nagpur 440016, INDIA E-mail: pravinkatare10@gmail.com Dr.Vilayat M. Kriplani Professor, Department of Mechanical Engineering G.H.Raisoni College of Engineering Digdoh Hill, Nagpur 440016, INDIA E-mail: v.vmk@rediffmail.com ABSTRACT The refrigeration industry has seen the rise and fall of a large number of refrigerants during the last 150 years. The research and development efforts in the field of refrigeration and air conditioning have always trying to find the alternative refrigerants which contribute to global warming. Conventional refrigerants are to be replaced by environment friendly working fluids. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are being substituted by hydrofluorocarbons (HFCs), hydrofluorooelifins (HFOs) and a variety of mixtures. It is important to estimate the thermodynamic properties of working fluids for simulation and efficient operation of thermal systems such as refrigerators and its performance. The proper working fluid must be chosen for the best performance of the system and the thermodynamic properties of those working fluids should be correctly evaluated. In this study the thermodynamic properties for the refrigerants R134a (HFC), mixture of hydrocarbon R290/R600a (50:50), R1234 yf (HFO) and R32 (HFC) have been investigated for the domestic refrigerator. Index Terms: Comparison, Alternative Refrigerant, R134a, Refrigerator I. INTRODUCTION Stratospheric ozone deplation as well as atmospheric greenhouse effect due to refrigerant emision have led to drastic changes in the refrigeration and air conditioning technology since the beginning of the 90s. With the introduction of the revised EU Ozone Depleting Substances Regulation in October 2000 and the introduction of a Climate Change Policy by the UK Government in November 2000, it is considered likely that more refrigeration system designers and users will be turning to alternative refrigerants such as HC, HFC and HFO. The increased application of this technology will bring with it many technical and safety issues. Hydrocarbons are excellent refrigerants, both for their energetic efficiency and their environmental compatibility witnessed by zero ODP and negligible GWP. Unfortunately, they are highly flammable and for this reason they are not widely applied. On the other hand, HFCs are good refrigerants, but due to their high GWP they could be not considered long term alternatives to traditional refrigerants, especially in view of the application of the Kyoto Protocol. Mixtures of HCs and HFCs are promising since they can contemporarily reduce the flammability of HCs and the GWP connected to HFCs.HFO like R1234 yf, the low GWP refrigerant has also been accepted in spite of flammability. A large number of development tasks have been completed. An extensive range of compressors and equipment is already available for the various alternative refrigerants. Most important criteria in this concern are flammability,thermodynamic properties and globle warming potential. Refrigerant selection and its properties Refrigerant selection is generally based on matching refrigerant vapour pressures to operating conditions, although this is not always the case. Refrigerants should also be selected so that they contribute to good system efficiency. With respect to blended refrigerants, these should only be selected when the effect of temperature glide and composition shift is not an issue. Refrigerant properties are necessary to describe the operating characteristics of the refrigerant within a system. In particular, physical properties of refrigerants are useful for determining the applicability of a refrigerant under design operating conditions. Thermodynamic and transport properties of refrigerants are necessary for predicting system behaviour and performance of components. Basic properties are provided in Table 1. 94 www.ijaegt.com

Table 1: Physical Properties of Refrigerants Leck (2009) presented modeling results for a basic thermodynamic cycle with a suction line heat exchanger and evaporation temperature of -2 C, which would be considered medium temperature refrigeration [7]. The results indicated that the COP of the R1234yf cycle would be between 1.7% and 7.2% lower than the R134a cycle depending on the condensing temperature, which was studied from 30 C to 56 C. Leck (2010) also presented modeling results for a basic thermodynamic cycle for medium temperature commercial refrigeration at an evaporation temperature of -10 C and a condensing temperature of 40 C [8]. The results indicated that R1234yf would have a 43% lower evaporation capacity and 7% better COP than the R404A, and an equal evaporation capacity and 1% lower COP than R134a. II. LITERATURE REVIEW One of the major segments of the refrigeration industry is the household refrigerator-freezer market. The widespread use of household refrigerator-freezers provides an opportunity for substantial energy savings, and the 100 million new units sold annually across the globe represent a considerable quantity of refrigerant [1]. Household refrigerators in the North American market typically use HFC-134a as a refrigerant because it has zero ozone depletion potential, favorable thermodynamic properties, and is non-flammable. The issue with R134a is that it has a relatively high 100-year GWP of 1,430 [2], which is a measure of its effect on the environment as a green house gas relative to carbon dioxide. Two alternative low GWP options that are being considered as replacements for R134a in household refrigerators are hydrocarbon mixture(r290+r600a) and HFO-1234yf. The household refrigerator-freezer sector is paying particular attention to these refrigerants as an R134a replacement due to the similar thermodynamic characteristics. Another reason that R1234yf is being considered as a replacement option for R134a is because it has a very low 100-year GWP rating of ~4, which is approximately 350 times lower than R134a [3], [4]. Among the various alternative low GWP refrigerant choices, one of the advantages of using R1234yf as an R134a replacement is that it shows promise as a direct drop-in replacement without system modifications because of the similar thermodynamic properties. The biggest issue for the acceptance and implementation of R1234yf is the fact that it is mildly flammable, which can create potential fire hazards for equipment which utilizes the refrigerant. The burning velocity of R1234yf has been found to be less than 10 cm/s, which qualifies it for the new 2L classification defined in ANSI/ASHRAE Standard 34 [5]. Pending new regulations, this classification has the potential to allow the implementation of R1234yf for household refrigerators, from which Class 2 refrigerants are currently banned [6]. Fujitaka et al. (2010) studied the performance of R1234yf as a drop-in replacement for R410A in a 4 kw room air conditioning application [9]. The ideal theoretical model predicted a 5.6% increase in COP when using R1234yf, while the experimental work showed a COP decrease of 58% and cooling capacity decrease of 30%. The differences between the theoretical model and the experimental work were attributed to the increased pressure drop of the pipes and the evaporator when using R1234yf, which would indicate that a system redesign would be required. A theoretical analysis was developed for R134a, propane (R290) and the mixtures of R290/R600a in the ASHRAE standard refrigeration cycle (evaporation temperature: -23.3 C, condensation temperature: 54.4 C) using the thermodynamic properties of REFPROP 6.0, as recommended by Kim et al. [10]. III. THEORETICAL MODEL The system has been developed for theoretical computational analysis of the cooling system in order to obtain estimates of the process of system operation as well as its performance. For this analysis the dedicated software, namely REFPROP 9.0 is used for evaluation of thermodynamic and thermo physical properties of refrigerants. A theoretical analysis was implemented for the use of R134a, mixture of R290/R600a (50%/50%), R1234yf and R32 in the ASHRAE standard cooling cycle (evaporation Temperature : - 23.3 C, condensation temperature : 54.4 C) using the thermodynamic properties of REFPROP 9.0.The ideal refrigeration cycle is considered for the working substances that change phase during cycle. It is known that the actual refrigeration cycle systems have some deviations from the ideal one due to pressure losses of fluid flow and heat transfer exchange between the surroundings. Cycle performance determination is performed to ease the theoretical calculations by means of some assumptions as follows: neglect of the 95 www.ijaegt.com

pressure drops and the heat losses to the environment from the devices evaporators and condensers, steady state operation is considered. Fig. 1 shows the thermodynamic cycle model used in theoretical and computational analysis. For drop in acceptance of working fluid in refrigeration system that already exists, some important performance characteristics should be considered. These are operating pressure, volumetric cooling capacity, coefficient of performance and compressor discharge temperature [11]. In the cycle analysis, the same cooling capacity was applied to all simulations of refrigerants considered. The cycle cooling capacity of 89 watt was obtained by conversion of freezing capacity of 165 L domestic refrigerator, provided by the manufacturer. Fig. 2 Vapour Pressure Vs evaporator Temperature Fig. 2 illustrates the variation of the saturation pressure as a function of the evaporator temperature for the four refrigerants. As shown in the figure, the mixture has the lowest pressure with mean pressure of 11.0% lower than that of R134a and R32 has the highest pressure. The pressure of R1234yf was very close to that of R134a. Refrigerant with low pressure is desirable in the system because the higher the pressure the equipment parts and accessories are also heavy in weight. Fig. 1 Real Thermodynamic model of a domestic refrigerator IV. RESULT AND DISCUSSION Applying the various equations in cooling circuit have shown in Fig.1 under predetermined conditions of operation (ASHRAE cycle) and using software REFPROP 9.0 were obtained operating data relating to selected refrigerants. Table 1 shows these results. The analysis of the variation of physical properties of refrigerants such as vapour pressure, density, viscosity, thermal conductivity, specific heat for liquids well as vapour for the temperature range -30 C to 20 C was considered. The theoretical results has been compared for four ozone-friendly refrigerants viz. R134a,R290/R600a(50:50) R1234yf and R32 in a vapour compression refrigeration system.these are shown in Figs. 2 to 12. Fig. 3 Liquid viscosity Vs evaporator Temperature Fig. 4 Vapour viscosity Vs evaporator Temperature 96 www.ijaegt.com

Figure 3 shows the characteristics of the refrigerants viscosity with different temperatures, it is observed that the liquid viscosity for R32 and the mixture had the lowest viscosity values across the temperature range.while as shown in fig. 4 the vapour viscosity for the mixture is lowest. This provides a reduction of pressure losses in the pipes of the refrigeration circuit. ability to dissolve the refrigerant in the lubricant. High levels of refrigerant solubility lead to reductions in viscosity of the refrigerant/lubricant, which is beneficial for the oil return to the compressor, but can act over the bearing lubrication. Fig. 7 Suction Volume Vs evaporator Temperature Fig. 5 Vapour Density Vs evaporator Temperature Fig. 5 presents that the vapor density of the R290/R600a (50:50) is lower for the whole range of operating temperatures, and thus an expected reduction in the work of compression required. The reduction in density is a more important factor than the latent heat of vaporization of the fluid Fig. 7 shows the variation in the suction specific volume conditions (suction temperature) of the compressor. It is observed that higher values of specific volume in the compressor suction provides a higher volumetric cooling capacity, resulting in the need for higher displacement of the compressor to the same cooling capacity of the system. It is observed that in order to carry out a drop-in of refrigeration system, the substitute fluid must have similar volumetric cooling capacity to the original fluid so as not to be necessary to replace the compressor. In this regard, it is observed that the R290/R600a (50:50) shows the highest specific volume. The R 32 and R1234 yf had values closer to R134a. Fig. 6 Liquid Density Vs evaporator Temperature According to fig. 6, the R290/R600a (50:50) gives the lowest liquid densities, providing thereby reducing frictional losses in the system. In any refrigeration system a portion of lubricating oil circulating with the refrigerant by the various components of the system. The oil effects are strongly correlated with the Fig. 8 Liquid Thermal Conductivity Vs evaporator Temperature 97 www.ijaegt.com

Fig. 9 Vapour Thermal Conductivity Vs evaporator Temperature Figures 8 and 9 have explained the liquid and vapour thermal conductivity of various refrigerants examined as a function of temperature. It is observed that R1234yf has the lowest conductivity throughout the temperature range. As the fraction of R134a is reduced, these values increase. The R290/R600a and (50:50) have higher conductivity throughout the temperature range. This fact provides a higher heat transfer rates to the refrigeration system. Fig. 11 Liquid specific heat Vs evaporator Temperature Fig. 12 Vapour specific heat Vs evaporator Temperature Fig. 10 Latent Heat Vs evaporator Temperature As shown in fig. 10, it can be noted that the latent heat of vaporization (refrigeration effect) of the R290/R600a is about twice that of R134a. However, due to the low specific volume of R134a in the suction, the volumetric cooling capacity of the two fluids are similar. As shown in Fig 11 and 12 the specific heat for mixture is highest as compared to other refrigerants. The ratio of specific heat calculates the isentropic work.the lowest ratio is desirable for lower isentropic work. 98 www.ijaegt.com

Table 2: Refrigerants computational parameters of ASHRAE cycle somewhat low, mixtures of medium GWP fluids such as R32 and low GWP refrigerants such as R1234yf may be the working fluids of choice in the immediate future. Meanwhile, the quest for better molecules continues. Barring new inventions, natural refrigerants appear to be the best choice in the long term. REFERENCE: [1] United States Environmental Protection Agency (EPA), 2010, Transitioning to Low-GWP Alternatives in Domestic Refrigeration, October 2010, <http://www.epa.gov/spdpublc/downloads/epa_hfc_domre f.pdf>. [2] Intergovernmental Panel on Climate Change (IPCC), 2007, IPCC Fourth Assessment Report: Climate Change 2007: Working Group 1: The Physical Science Basis: 2.10.2 Direct Global Warming Potentials, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Analyzing the Table 2 can be noted that the latent heat of vaporization (refrigeration effect) of the R290/R600a blend is about twice that of R134a. However, due to the low specific volume of R134a in the suction, the volumetric cooling capacity of the two fluids is similar. In order to accept a working fluid as a replacement for a domestic refrigeration system, a similar volumetric cooling capacity and performance compared with the original refrigerant are required [11]. Due to increase in cooling effect and decrease in specific volume, Volumetric cooling capacity increases which means that the higher the VCC the smaller is the size of compressor required. The VCC obtained for R152a was 3.5% higher than that of R134a, while that of R32 was 25.2% lower than that of R134a. Therefore, bigger size of compressor is required for R32. The VCC for R1234 yf is quite close to that of R134a. V. CONCLUSION The research and development efforts in the field of refrigeration and air conditioning apply to use HFCs that replaced CFCs in the last decade have high GWP and need to be eventually phased out. Environment friendly natural refrigerants such as ammonia, carbon dioxide, hydrocarbons have specific practical deficiencies that limit their universal use. Recently suggested HFOs have low GWP compared to natural refrigerants, but are flammable. The thermo-physical properties, restrictions 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 vapour phases, high latent heat, and small temperature glide are the desired thermo-physical properties of refrigerant mixtures in the literature. As a result of the analysis in this paper, the energy efficiency of HFOs is [3] Wilson, D., and Koban, M., 2009, HFO-1234yf Industry Update, EPA R1234yf Commercialization Meeting, February 6, 2009. [4] Papadimitriou, V., Talukdar, R., Portmann, R., Ravishankara, A., and Burkholder, J., 2008, CF3CF=CH2 and (Z)-CF3CF=CHF: Temperature Dependent OH Rate Coefficients and Global Warming Potentials, Physical Chemistry Chemical Physics, Vol. 10, pp. 808 820. [5] American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE), ANSI/ASHRAE Standard 34-200: Designation and Safety Classification of Refrigerants. [6] Underwriters Laboratories (UL), 2011, White Paper: Revisiting Flammable Refrigerants, Underwriters Laboratories Inc. [7] Leck, T., 2009, Evaluation of HFO-1234yf as a Potential Replacement for R-134a in Refrigeration Applications, 3rd IIR Conference on Thermo physical Properties and Transfer Processes of Refrigerants, Boulder, CO, USA, June 23-26, 2009. 8] Leck, T., 2010, New High Performance, Low GWP Refrigerants for Stationary AC and Refrigeration, International Refrigeration and Air Conditioning Conference, Purdue, July 12-15, 2010. [9] Fujitaka, A., Shimizu, T., Sato, S., and Kawabe, Y., 2010, Application of Low Global Warming Potential Refrigerants for Room Air Conditioner, 2010 International Symposium on Nextgeneration Air Conditioning and Refrigeration Technology, Tokyo, Japan, February 17-19, 2010. 99 www.ijaegt.com

[10]Kim,M.H.,Lim, B.H. and Chu,E.S.,1998,The performance analysis of a hydrocarbon refrigerant R600a in a household refrigerator/freezer,ksme International Journal Vol. 12,No. 4,pp 753-760 [11] Fatouh, M. and EI Kafafy, M. 2006, Assesment of propane/commercial butane Mixtures as possible alternatives to R134a in domestic refrigerators, Energy conversion and management, Vol.47, pp 2644-2658. 100 www.ijaegt.com