Transcritical carbon-dioxide refrigeration systems with ejectors rely on the interactions between the high-pressure liquid supplied from the condenser and the low-pressure vapor supplied from the evaporator to enable efficient pressure recovery. The liquid is accelerated through a convergent nozzle (motive), which develops a jet. The jet drags the vapor (suction) using shear interactions. A deeper understanding of the interface physics and turbulent flow during the entrainment process is needed to guide internal shape optimizations. This paper focuses on the evolution of coherent structures and their effects on the entrainment of vapor into the liquid jet. The Reynolds numbers (Re) of the liquid jet and the induced vapor flow are 1.2 × 105 and 9.8 × 104, respectively. The pressure difference between the vapor inlet and the ejector outlet is −4.92 bar. Large-eddy simulation is used to understand the physics. Compressibility is important only near the nozzle throat. The downstream flow begins as strongly multiphase. Kelvin–Helmholtz instabilities at the liquid−gas interface trigger perturbations, which form “Ring” vortices. An azimuthal instability leads to waviness in a Ring vortex, which rapidly develops turbulence through vorticity redistribution. As turbulence develops, the flow regime transitions from two-phase flow to essentially single-phase flow without strong density variations. Maximum kinetic energy transfer between the liquid jet and suction vapor flow, responsible for entrainment, occurs in the strongly two-phase regime, showing that shear is more efficient than turbulence and phase change for mobilizing the vapor flow.
Bhaduri et al. (Mon,) studied this question.