CFD simulations of a two-phase ejector for transcritical CO2 cycles applied to supermarket refrigeration systems.

The use of carbon dioxide (CO2), as a working fluid for large refrigeration systems, has grown tremendously in recent years. Factors such as its low cost, easy accessibility and environmentally friendly characteristics compared to HFCs and HCFCs, has made CO2 a viable alternative. To efficiently operate with CO2, the thermodynamic cycle needs high-pressure levels that can easily exceed the critical point due to the low critical temperature. By replacing conventional expansion valves with ejectors, the thermodynamic losses of the high-pressure throttling are mitigated, and the overall system performance is improved. To design and efficiently control the whole cycle, a thorough comprehension of the ejector fluid dynamics is mandatory. In this work, Computational Fluid Dynamics (CFD) is used to thoroughly investigate such a device. The employed CFD solver uses a modified form of the Homogenous Relaxation Model (HRM) to deal with twophase flows in a non-thermodynamic equilibrium state, per Colarossi et al. (2012). Preliminary numerical results for an ejector in supermarket refrigeration system operating conditions are presented and discussed.