Numerically Optimized Ejector Geometry for Ejector Refrigeration Systems with low-GWP Working Fluids

Abstract

Recently, an ejector refrigeration system (ERS) is a promising cooling strategy with waste heat utilization and minimization of power consumption by evading the compressor. However, analyzing the intricate flow structure inside the ejector and corresponding COP enhancement are major challenges of an ERS. The type of working fluid, design specifications, and working conditions significantly affect the ejector behavior. The environmental issues caused by leakage of the most popular high GWP refrigerant R134a divulge the need for low GWP alternatives. Moreover, the effect of critical design specifications such as area ratio (AR) and nozzle exit position (NXP) for these alternatives are not explored yet. Therefore, five low-GWP alternates for R134a, namely: R1234yf, R1243zf, R152a, R513a, and R440a, are tested numerically under wide-ranging operating conditions. In addition, the ejector performance for all refrigerants is examined for seven distinct ARs and five different NXPs. The effect of the refrigerant variant and NXP on the internal flow structures of the ejector is also analyzed. Besides, the study is extended to find the optimal NXP at various operating temperatures using R1234yf refrigerant. In most cases, the higher entrainment ratio (ER) is obtained with R1234yf and R1243zf, and the increase in AR has a positive effect on ER. The impact of NXP is higher at condenser temperature with minimal waste heat in the generator. Irrespective of the operating conditions for R1234yf, the optimum NXP is obtained as 10 mm, which is 1.67 times the constant-area mixing chamber diameter.