Mixer diameter significantly influences the performance of two-phase ejectors. This study proposes a design method for the mixer diameter of two-phase ejectors based on the turbulent jet mixing mechanism. When the mass flow rate of the mixed jet increases to the target total mass flow rate of the ejector

the diameter of the jet's external boundary should be the optimal mixer diameter. The mixer diameter of a CO2 ejector is optimized based on this method. The optimal diameter is 2.4 mm when the entrainment ratio is 0.5. The performance of the two-phase CO2 ejector is investigated for varying mixer diameters via numerical simulation. The results show that the optimal diameter is 2.2 mm under the same condition. When the mixer diameter is 2.4 mm

the pressure lift is 0.9 MPa

which is 57.9% higher than the baseline performance. Based on the turbulent jet theory

this study also proposes a correlation for the dimensionless optimal mixer diameter. The dimensionless optimal mixer diameter ranges from 1.7 to 2.1 when the entrainment ratio is 0.4–0.8. The correlation exhibits a -6%–10% deviation from the CFD simulation results and can be used to predict the optimal diameter.