A concept of performance improvements for R744 two-phase ejector with bypass duct.

A concept of the two-phase ejector with a bypass duct for CO2 applications is proposed in this study. A geometry and bypass positioning, idea of regulation as well as integration with suction nozzle duct was designed and described. Preliminary numerical analysis of the proposed bypass geometry was performed. Computational platform ejectorPL integrated with well validated mathematical model of transcritical R744 two-phase flow were used. Gas cooler and evaporator conditions characteristic for large systems such as supermarket refrigeration units were examined. Separation pressure of 32 bar in liquid receivers were simulated for the bypass variants with two duct shapes and six attachment positions. The perspective results were obtained for this low pressure conditions. Namely, the suction mass flow rate increment was of 36.9% for the bypass angle of 19°. Hence, the bypass implementation resulted in the efficiency improvement from 22.2% to 30.4%. Significant influence of the bypass geometry into the overall ejector efficiency was reported. Finally, a possible shape optimisation of bypass duct as well as further analysis focused on the regulation and control strategy were given.