Numerical Modelling of a Novel Two-Stage Linear Refrigeration Compressor

Abstract

Linear compressors have started to applied in refrigeration owing to their oil-free operation, capacity modulation by variable stroke and higher seasonal efficiency. Nevertheless, linear compressors are subject to a high seal leakage loss and piston offset (drift) particularly at high pressure ratios. Meanwhile, there is a reduction in the accuracy of resonant frequency prediction due to very nonlinear gas spring at high pressure ratios, leading to a reduction in the compressor efficiency. A two-stage operation is considered as a feasible solution to the aforementioned issues, given that each stage can operate at lower pressure ratio while producing sufficient cooling capacity. A numerical model of two oil-free linear compressors using R1234yf for two-stage compression is presented in this study to investigate the characteristics of the system in various operating conditions. The mean absolute percentage errors (MAPEs) of the predicted mass flow rate and power input are 2.47% and 8.49%, respectively. The coefficient of performance (COP) is 5.5 for a two-stage compression system and 2.0 for a single-stage compression system while the condenser temperature and evaporator temperature are 50 °C and -23 °C, respectively. The two-stage compression system offers superior performance to the single-stage system.