An analysis of homogeneous relaxation model accuracy for the CO2 expansion inside the two-phase ejector.

Abstract

In this study, the CO2 expansion inside the two-phase ejector was modelled. To simulate the two-phase flow inside the device, two models were applied, namely homogeneous equilibrium model (HEM) and homogeneous relaxation model (HRM). The two-phase flow models were implemented on the effective computational tool called ejectorPL. This script guarantee the fully automated and systematic computations for various ejector shapes and operating conditions. Originally, only the HEM approach was implemented in ejectorPL. However the accuracy analysis of the HEM showed lack of model fidelity for the operating conditions far from the carbon dioxide critical point. The simulated motive nozzle mass flow rate showed very good agreement with the experimental values for the operating regimes, while for the points far from the critical point the motive nozzle mass flow rate was underestimated. To improve the ejectorPL performance, the HRM was applied to simulate the refrigerant flow inside the ejector. Then, the accuracy of that approach was evaluated. To assess the accuracy of the model, the computed motive nozzle and suction nozzle mass flow rates were compared with the experimental data. The operating conditions used for that analysis were typical for the supermarket refrigeration system. The results of the HRM accuracy analysis and the difference between the HEM and HRM accuracy for the specific operating regimes will be presented in 12th IIR Gustav Lorentzen Natural Working Fluids Conference.