Effects of Mixer Length and Diffuser Angle on Two-Phase CO₂ Ejector

This study employed a validated computational fluid dynamics (CFD) model to investigate the influences of the mixer length and diffuser angle on the ejector pressure-recovery performance. The results demonstrated that an optimal combination of mixer length and diffuser angle exists at which the ejector has the highest performance. The effects of these two geometrical parameters on the ejector performance were highly consistent. When the mixer length was sufficiently long, the mixing was sufficient, and the mixed flow was not subjected to separation during pressure recovery. Under these circumstances, the effect of the diffuser angle on the ejector performance was relatively trivial, varying between 0.5° and 3°. However, when the mixer length was short, the flow was prone to turbulent losses near the diffuser wall. In this case, the effect of the diffuser angle was significant. In addition, the optimal geometries were affected by the operating conditions. The optimal mixer length increased as the nozzle inlet pressure and temperature decreased, whereas the optimal diffuser angle decreased. Under the conditions and nozzle configuration investigated in this study, the optimal mixer length was approximately 38 mm and the optimal diffuser cone half angle was between 1° and 1.5°.