Abstract:
The refrigeration industry today needs refrigerant with global warming potential (GWP) ≤ 150 - in accordance with the European Union protocol, alongside other ideal properties, which a single chemical refrigerant have not met as at today. This has led to theconnsideration of refrigerant blends for possible solution. The aim of this work is to investigate the performance of refrigerant blends with estimated GWP ≤ 150. Thus, R-134a and R-600a of known GWP (1300 and 3 respectively) were blended at ratios 11%/89%, 7.5%/92.5% and 3.6%/96.4% to form new refrigerant blends K, L, M, with expected GWP of 150, 100 and 50 respectively. The ratios were determined by Ali’s model, used to estimate the GWP of refrigerant blends when those of the individuals are known. The flammability of the blends were tested by igniting with a flame, before being charged into a domestic compression system, where they were run simultaneously with systems using R-134a and R-600a. Their respective operating temperatures and pressures were obtained with the aid of thermometers and barometers attached to the evaporator, condenser and compressor of the systems with readings taken every 5 minutes during the experimentation. The flammability test indicated they were slightly flammable. The results obtained when subjected to same operating conditions: ambient temperatures (37oC, 32oC), compressor power, mass charge (1 kg) and flow-rate (0.05 kg/s), with R-134a and R-600a showed they attained lower evaporator temperatures (-3.1oC, -3.7oC and -4.7oC for blends K, L, M respectively at 37oC; and -3oC, -4oC and -4.8oC at 32oC) to R-134a (7.7oC and 6.2oC) but higher temperatures to R-600a (-5.3oC and -6.5oC); and have close pressure ratio (5.5 bars and 5.3 bars). Analysis of the obtained results showed coefficient of performance (COP) of: 0.8389, 1.0708, 1.0898, 1.1181, and 1.1373 at 37oC ambient temperature; and 0.8283, 1.0923, 1.1254, 1.1579, and 1.2159 at 32oC ambient temperature, for R-134a, blends K, L, M and R-600a respectively. These imply, the blends can replace R-134a in domestic vapour refrigeration system without changing: existing piping system (due to their close operating pressure), cooling methods, and lubricants, and still achieve higher COP, except that, they are slightly flammable. That blend K offers a significant improvement in flammability compared to R-600a alongside higher COP to R-134a, makes it the best alternative of the three blends for domestic systems.
