Modified homogeneous relaxation model for the R744 trans-critical flow in a two-phase ejector

Abstract

The proposed modified homogeneous relaxation model (HRM) applied to the numerical model of a CO2 two-phase ejector was numerically investigated and developed based on the optimisation of the relaxation time (RT) correlation. The optimisation procedure was performed using a genetic algorithm. The study of the RT definition on model accuracy was carried out using literature correlations and constant relaxation time, and by comparing the developed modified HRM with experimental results. The modified HRM showed the higher accuracy of the motive nozzle mass flow rate (MFR) than that of the other available numerical models for the subcritical operating regimes and similar high accuracy as the homogeneous equilibrium model (HEM) for the trans-critical operating regimes. The application range of the modified HRM was defined for the motive nozzle pressure above 59 bar to predict the motive nozzle MFR with the relative error below 15%. For the motive nozzle pressure level below 59 bar, the modified HRM improved the accuracy of the motive MFR prediction by 5%–10% compared to the HEM formulation.