Thermodynamic analysis on a two-stage transcritical CO2 heat pump cycle with double ejectors

• Published in: Energy conversion and management Vol. 88; pp. 677 - 683
• Main Authors: Xing, Meibo, Yu, Jianlin, Liu, Xiaoqin
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2014; Elsevier
• Subjects: Applied sciences; Carbon dioxide; Devices using thermal energy; Ejector; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Heat pump; Heat pumps; Two-stage system; Two-stage system; Ejector; Heat pump; Performance; Carbon dioxide; Thermodynamic analysis
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2014.09.025

•Double ejectors are applied in a two-stage transcritical CO2 heat pump cycle.•The performance of the new cycle with double ejectors is evaluated theoretically.•The new cycle exhibits higher performance compared to the basic two-stage cycle.•The heating COP can be increased by 10.5–30.6% under given operation conditions. In this study, two ejectors are proposed as expansion devices for a two-stage transcritical CO2 heat pump cycle to enhance the cycle performance. The two ejectors are arranged at the low- and high-pressure stages, respectively, to recover more available expansion work, and significantly reduce the throttling loss at each stage. The performance of the improved two-stage cycle is evaluated by using the developed mathematical model, and then compared with those of the basic two-stage cycle with a flash tank. The simulation results show that the improved two-stage cycle exhibits higher heating COP and volumetric heating capacity compared to the basic two-stage cycle. By further incorporating an internal heat exchanger, the heating COP can be increased by 10.5–30.6% above that of the baseline cycle when the subcooling degree varied from 0 to 15°C under given operation conditions of −15°C evaporating temperature, 10MPa gas cooler pressure and 35°C outlet temperature. Additionally, the effects of the gas cooler pressure and intermediate pressure on the maximal heating COP are also discussed.