In this study, computational fluid dynamics (CFD) was used to investigate the performance of the steam ejector used in refrigeration systems to increase operational flexibility and COP. A 2Daxisymetric model of a two-stage ejector (TSE) was developed and its performance was compared to that of the commonly used single-stage ejector. The SST k-omega (k-ω-sst) model was applied as a turbulence model. In the simulation, the TSE was analyzed using generator temperatures between 100 and 130°C and evaporator temperatures between 0 and 15°C, as in a previous study. The CFD simulation results showed that the TSE provided high entrainment ratios up to 77.2% while showing a marginal decrease in the critical back pressure up to a maximum value of 21.9%. Therefore, it can be concluded that the TSE can significantly benefit refrigeration systems requiring high refrigerating capacity while maintaining a slightly low condensing pressure.

Abstract. In this research, performance of a hybrid compressor and ejector refrigeration system for automotive air conditioning application was investigated theoretically and experimentally. Mathematical modeling integrated the 1-dimensional analysis of ejector with the thermodynamic analysis of the hybrid compressor and ejector refrigeration system via EES (Engineering Equation Solver) software was proposed. Also an experimental rig of the hybrid compressor and ejector refrigeration system for automotive air conditioning application was built. This hybrid system has a rated cooling capacity of 3.5 kW. Refrigerant R134a and R141b were used for mechanical vapor compression sub system and the ejector sub system, respectively. The operating conditions are chosen accordingly as, generator temperature between 100 °C and 120 °C, condenser temperature between 30 °C and 40 °C, and evaporator temperature between 0 °C and 10 °C. Theoretical results of the ejector's entrainment ratio (Rm) and COP of the system with variations on operating conditions were compared with the experiment values. From the results, mathematical modeling seems to provide error in COP prediction up to 15.5% when compared with experimental values. Fortunately, modification of the mathematical modeling by applying the computational fluid dynamics (CFD) technique provides less error about 5.5%. It's also found that the COP of the hybrid system can be increased by 10-20% compared to a simple stage ejector refrigeration cycle (EJC). Moreover, estimated power consumption of the automotive air conditioning system can be approximately reduced 20% under the conventional vapor compression cycle.