Numerical modeling of a novel two-stage linear refrigeration compressor

Linear compressors have started to apply 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. Two-stage operation is considered as a feasible solution to the aforementioned issues due to the lower pressure ratio for each stage. A numerical model of two-stage compression system using linear compressors is presented in this study to investigate the system performance under various operating conditions. The proposed numerical model consists of a thermodynamic sub-model, a piston dynamic sub-model and a reed valve dynamic sub-model. Experiments are also conducted based on a refrigeration system with two linear compressors connected in parallel to validate the proposed model. The mean absolute percentage errors of the predicted mass flow rate and power input are 2.47% and 8.49%, respectively. The modeling results show that the coefficient of performance 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.