Performance analysis of dual ejector-expansion air source heat pump cycle with three-stage evaporation for cold region application

Abstract

In the present study, a modified dual ejector-expansion heat pump cycle with three-stage evaporation has been proposed for air source heat pump applications in cold region. This cycle layout could lead to an improvement in cycle performance due to much expansion work recovery and better temperature variation matching between cooled air and refrigerant. The performance analyses of the proposed cycle and ejectors using refrigerant R290 have been conducted at different operating conditions. In addition, the performance characteristics of the cycle are compared to those of the baseline cycles using a conventional expansion device, as well as a single ejector and a single evaporator. Through thermodynamic analyses, it is found that the improvements in the coefficient of performance of the proposed cycle can reach up to 26.1% and 10.5%, respectively, as compared to the basic vapor-compression heat hump cycle and ejector-expansion heat hump cycle. The exergy destruction of the proposed cycle can be reduced by 28.6% and 13.6% than those of the other two basic cycles. In addition, the performance of ejectors under different operating conditions is studied. The pressure lift ratio of the ejector in the new cycle varies from 1.36 to 1.69, which shows 14.3%∼21.6% improvement compared to the basic ejector-expansion heat pump cycle. Overall, this paper confirms the performance advantages of the proposed new heat pump cycle and its potential application in an air-source heat pump system.