Optimization of the two-stage ejector with blocking area ratio of primary nozzle throat under certain liquid volume fraction in two-phase inlet fluids

This paper proposes an innovative two-stage ejector with a needle blocking the main nozzle area within 0%-60% to control the mass flow rate of the inlet. Based on this, under certain liquid volume fraction in two-phase inlet fluids, the nozzle exit positions (NXP₁ and NXP₂) and constant-area mixing chamber lengths (L₁ and L₂) of the first and second stages were optimized with blocking area ratio (BAR) of primary nozzle throat by using CFD simulation, the working fluid is R134a. The main results are as follows: (1) The maximum increase rate of the entrainment ratio (ER) of the first and the second-stage with optimization of four geometries without needle blockage are relatively slight, in comparison, both of them with optimization of L₁ can reach 23.47% and 20.38%, which obtain the best improvement; (2) Under the condition of a needle blockage at the primary flow inlet of the first-stage ejector, the increase rate of ER₁ with optimization of NXP₁ and L₁ are close to that without needle blockage; (3) Under the condition of a needle blockage at the primary flow inlet of the second-stage ejector, the first-stage ejector can achieve relatively large improvement of ER, especially, the optimization of NXP₂ can increase the maximum ER₁ by 258.73% of initial value, and the optimization of L₂ can increase the maximum ER₁ by 239.38% of initial value. The study in this work is helpful to understand the two-stage ejector performance improvement by adjusting the blocking area ratio of primary nozzle throat under certain liquid volume fraction in two-phase inlet fluids.