Mixing layer effects on the entrainment ratio in steam ejectors through ideal gas computational simulations

• Ejector entrainment ratio ER is influenced by pressure-driven and mixing layer effects.
• The significance of pressure driven effects on ER is specified through inviscid CFD simulations.
• The difference between ER based on viscous and inviscid simulations specifies entrainment due to mixing layer effects.
• ER is increasingly influenced by pressure driven effects when the secondary stream pressure increases.
• Mixing layer effects have an increasing influence on ER for lower secondary stream pressures.

Ejector entrainment ratios are influenced by both pressure-driven effects and the mixing between the primary and secondary streams, but the significance of each factor has not been identified in prior literature. This paper presents a computational simulation investigation of flow in a representative steam ejector to specify the contribution of mixing and pressure-driven effects to the overall ejector entrainment ratio under different operating conditions. The simulation of mixing layer growth was validated by using experimental data available in the literature, while the application of the computational method to the ejector flows was validated using static pressure distribution and entrainment ratio data in the particular experimental ejector arrangement. Simulation results show that under a fixed operating condition for the primary and discharge streams, at lower secondary pressure the ejector entrainment ratio is more strongly influenced by the mixing effects. For the particular ejector and the operating conditions considered herein, about 35% of the ejector entrainment ratio is due to mixing effects when the secondary stream pressure lift ratio is 4.5, while this portion is reduced to about 22% when the secondary stream pressure lift ratio is 1.6.