Thermodynamic Properties of HFC-32/HFC-125 Mixtures and an Estimation of Its Environmental Impact and Utility in Refrigeration

A cubic equation of state for HFC-32/HFC-125 mixtures developed on the basis of our experimental data was used for thermodynamic analysis of refrigeration cycles using this blend. The influence of composition changes on energy efficiency and Total Equivalent Warming Impact (TEWI) was studied. Comparisons of this blend with HCFC-22 and other alternative refrigerants were also carried out. Detailed comparisons have been made for refrigerants R410A and R41 OB on the basis of the calculated coefficient of performance (COP). INTRODUCTION Among the small number of alternatives proposed as substitutes for the widely used working fluid, HCFC-22, the mixture HFC-32/HFC-125 has good long-term prospects for domestic and medium-temperature commercial refrigerating appliances, heat pumps, chillers and especialy general air conditioning applications [ 1-7]. On the basis of this mixture, the following working fluids were recently developed: mixture HFC-32/HFC-125 50150 wt.%, assigned R-410A by ASHRAE and mixture HFC-32/HFC-125 45/55 wt.%, assigned R-410B by ASHRAE . In comparison with HCFC-22 these blends have much higher saturation pressures versus temperature and capacity that require complete systems redesign. Alternatively, refrigerant systems optimised for R-410A and R-410B display a slightly better energy efficiency than existing systems using HCFC-22 due to more favorable vapor pressures level for the compressor [6, 7]. In addition, the HFC-32/HFC-125 blend belongs to class of near-azeotropic mixtures and has a temperature glide less than 0.1 within the entire concentration and temperature interval, which is useful in technological applications of the mixture as a refrigerant (the issues of filling and refilling the working fluid, its solubility in oils, constancy of its composition inside the compressor, condenser and evaporator). In addition, specific refrigerating effects, coefficients of performance (COP) and heat transfer coefficients for R-410A and R410-B refrigerants are higher than the corresponding properties for the other binary mixtures alternatives [7, 8]. However, there are some contradictions in estimation of the coefficient of performance for HFC-32/HFC-125 by different authors [1, 3, 7-10]. Some thermodynamic cycle analyses [3, 10] indicated a slightly better coefficient of performance for HCFC-22 in comparison with R-410A. Alternatively, others [1, 7] have drawn attention to the possibility of improving the COP for HFC-32/HFC-125 by properly calculating of influence of transport properties and optimizing of heat exchangers in re-designed systems. It is obvious that the calculation of the energy efficiency of this mixture should to be done on the basis of reliable thermodynamic properties. In present paper, our experimental PVT-data [11] and data by Sato et al. [12] have been used to develop an equation of state for HFC-32/HFC-125 blend. This equation of state then applied to calculate COP and compare energy efficiencies of this mixture with HCFC-22 and other alternatives. The possible long-term influence of using HFC-32/HFC125 is also considered. EQUATION OF STATE The data sourses for developing an equation of state for the HFC-32/HFC-125 blend in the vapor region included our experimental data [11] on the vapor-liquid coexistance curve and in the vapor state for compositions of 13.15, 45.00