Multiphase Mixture Simulations of a Specific Two-Phase R-744 Ejector Geometry

Two-phase carbon dioxide (R-744 or CO₂) ejectors are energy recovery devices of the transcritical R-744 vapor-compression refrigeration systems to counteract the energy loss at the throttling stage. However, understanding of the multiphase mixture inside the ejector geometry is complex from the viewpoints of multiphase turbulent mixing, transcritical expansion, and high-velocity flow profile. This study reports on Computational Fluid Dynamics (CFD) simulations for a specific two-phase R-744 ejector geometry with two inlets (motive inlet and suction inlet), a single outlet, and converging-diverging nozzle geometry. Four operationally different cases are investigated, all of them featuring supercritical motive nozzle inlet conditions and saturated or superheated gas suction nozzle inlet conditions. The CFD study is performed in the Simcenter STAR-CCM+ CFD environment using the Two-Phase Thermodynamic Equilibrium Model that represents a coupled multiphase mixture solver for the continuity, momentum, and energy equations for compressible flow phenomena. A comparison of the results with experimental data from the literature shows that the mass entrainment ratio deviates between 3.2% to 8.3%. The relative errors of the motive and suction mass flow rates are in the ranges of 15.7% to 21.7% and 0.1% to 12.4%, respectively. Detailed analysis of the fields of pressure and velocity are provided.