Experimental investigation of R-134a and R-600a refrigerant blend in domestic vapour compression refrigeration system
The refrigeration industry today needs refrigerants with global warming potential (GWP) ≤ 150 according to the European Union protocol, alongside other properties, which no single refrigerant has met as at today. This study focused on blending of existing refrigerants towards obtaining blends with GWP ≤ 150. It investigated the performance of blends of two existing refrigerant, R-134a and R-600a, blended together at ratios of 11%/89%, 7.5%/92.5% and 3.6%/96.4% to form blends K, L and M respectively. The blends were to have, according to the blending ratios, estimated GWPs ≤ 150 using Ali’s model. The blends flammability was tested and the blends were then charged into domestic vapour compression systems, where their operating temperatures and pressures were obtained every 5 minutes during the experimentation. The flammability test shows they are flammable while results obtained at ambient temperatures (37oC, 32oC) under same operating conditions indicated evaporator temperatures (7.7oC, -3.1oC, -3.7oC, -4.7oC, -5.3oC) ; (6.2oC, -3oC, -4oC, -4.8oC, -6.5oC) for R-134a, K, L, M and R-600a respectively. Also the analysis of the results gave corresponding average Coefficient of Performance (COP) of (0.8389, 1.0708, 1.0898, 1.1181, and 1.1373) and (0.8283, 1.0923, 1.1254, 1.1579 and 1.2159) for the aforementioned respective refrigerants at ambient temperatures of 37oC and 32oC, respectively. Thus, the blends can replace R-134a without changing pipe, cooling method and lubricants and still obtain higher COP, though mildly flammable−having slow burning velocity and low heat of combustion. That blend K offers significant improvement in flammability compared to R-600a alongside higher COP to R-134a, makes it the best alternative of the blends.
Keywords: Coefficient of Performance (COP), Vapour Compression Refrigeration System, Flammability, Global warming Potential (GWP), Refrigerant, Refrigerant blend