Numerical analysis and optimization of CO2 vapor injection heat pump cycle with two phase ejector.

Refrigeration and air conditioning industry is influenced by environmental issues such as global warming and air pollution. Therefore, new refrigerants for solving and preventing global warming problem are strongly required. In this reason, natural refrigerants are getting attention again. Among many natural refrigerants, carbon dioxide has a lot of advantages as a refrigerant. However, simple CO2 heat pump cycle has low COP compared to that of other cycles with commercial refrigerants. In this study, to enhance the performance of heat pump system using CO2 refrigerant, a novel vapor injection cycle equipped with an ejector is proposed and its performance is analyzed. By using an ejector to feed extra refrigerant into vapor injection line, the cycle can utilize expansion energy of refrigerant and reduce compression work. The performance of this cycle can be changed by many cycle characteristic variables. The injection pressure and the mass flow rate are the major parameters which influence the performance of vapor injection cycle. Ejector performance and the mass flow rate ratio of the primary and secondary flows can also be main parameters of this cycle. The effect of these parameters on the target cycle performance is investigated. From these results, optimization of this cycle is conducted.