This study proposes an optimization guideline for a two-phase ejector's nozzle exit position (NXP) based on the turbulent jet mixing mechanism. Under a given suction mass flow rate

the optimal NXP is the distance that the jet travels when the external boundary of the jet increases to the mixer radius. The performances of two-phase CO2 ejectors with NXP values of 3

5

7.5

10

and 15 mm were studied by numerical simulations. The results show that when the NXP is 5 mm

the jet mixing pattern can exactly satisfy the above guidelines. In this case

the ejector has a maximum pressure-lift of 0.69 MPa

46.8% higher than that of the 15 mm case. By analyzing the jet velocity profiles on different cross-sections in the suction chamber

we show that if the NXP is greater than the optimum value

the external jet boundary will exceed the mixer radius

preventing part of the jet flow from entering the mixer. In addition

a vortex region appears near the suction chamber wall

resulting in jet energy dissipation and thus degrades pressure recovery. When the NXP is less than the optimal value

the entrainment process is completed in the mixer

and the effective length is reduced

causing a 1.5% decrease in pressure recovery. This study is enlightened by the jet velocity characteristic and proposes a correlation for the initial guess of the optimal NXP

which shows a 4.2% deviation from the CFD result.