A Parametric Study on the Effect of Mixing Chamber for Expansion Work Recovery CO2 Ejector

A numerical study of supercritical CO 2 two-phase flow in the ejector was carried out by computational fluid dynamics (CFD) methods. Through the comparison of simulation results and available experimental data in the literature, the accuracy of the three-dimensional CFD model was verified. A comparison of the effects of four turbulence models on the simulation calculation results was also presented. The distributions of pressure, velocity, two-phase volume fraction, shock wave and exergy flux inside the ejector were analyzed. The effects of the mixing section geometry on the performance of the ejector were obtained. Then, the entrained performance of the ejector was investigated by changing the area ratio between the constant-area mixing chamber and the outlet of the motive nozzle (AR) and the ratio between the length and the diameter of the constant-area mixing chamber (LDR). Finally, the optimum AR and LDR were determined to be 8.3 and 8.1, respectively based on the maximum entrained ratio and the minimum exergy destruction. Through optimizing the mixing chamber geometry, the minimum total exergy destruction and the maximum mass entrainment ratio (MER) of the ejector can attain 0.33 J/(kg·K) and 0.698 respectively.