Performance analysis of an ejector-assisted two-stage evaporation single-stage vapor-compression cycle

Abstract

• An ejector-assisted 2-stage evaporation 1-stage vapor-compression cycle is proposed. • New cycle works for different refrigerants, especially for CO 2 transcritical cycle. • Energy savings depend on reasonable design and variable operating conditions. For actual vapor-compression refrigeration or heat pump systems with variable-temperature heat reservoirs, two-stage evaporation cycle is an efficient way to improve the coefficient of performance (COP). However, its application is limited because the two-stage evaporation cycle requires two individual suction pressures carried out by two cylinders or two compressors. To solve this problem, a two-stage evaporation cycle with a common single-stage compressor is proposed. An ejector is applied to lift the lower evaporation pressure up to the higher evaporation pressure or the compressor suction pressure. A thermodynamic model is developed to analyze its performance. Numerical results indicate that the COP of the novel cycle is 12.1% higher than the ejector cycle, 6.9% higher than the two-stage evaporation cycle and 22.0% higher than the basic refrigeration cycle under rated operating conditions. The exergy analysis indicates that TSEC-E can reduce 49.6% exergy loss of expansion process and 21.5% exergy loss of heat transfer process in evaporators in comparison with the basic refrigeration cycle. Although TSEC-E is applicable with various refrigerants, particularly it is more effective for CO 2 transcritical cycle. Moreover, performance improvement of the novel cycle under variable operating conditions is numerically investigated.