Abstract:

Two-stage compression is an effective method to improve the coefficient of performance（COP）of trans-critical refrigeration cycle of CO₂，and COP of a complete inter-cooling mode is higher than that of an incomplete mode. For the trans-critical throttling cycle of CO₂ in a two-stage compression with complete inter-cooling，the throttling cycle can be divided into two types，single-throttling（STDC）cycle and double-throttling（DTDC）cycle. For these two cycles，the effects of outlet temperature of gas-cooler and heat rejection pressure on the COP are investigated，and compared with those in a single-stage compression（STSC）.The results indicate that under given condition，DTDC cycle presents the maximum COP，while the STDC cycle presents the highest optimum high pressure. For the three cycles，increase in gas-cooler outlet temperature decreases the COP，increases the optimum high pressure，and decreases the isentropic compression efficiency. The optimum inter-cooling pressure for STDC cycle and DTDC cycle deviates from the geometric mean of high pressure and low pressure，but this has little effect on the system performance.