Application range of the HEM approach for CO 2 expansion inside two-phase ejectors for supermarket refrigeration systems, International Journal of Refrigeration (2015), http://dx.doi.org/ HighlightsThe accuracy of the HEM approach for the R744 expansion inside ejectors was assessed.The HEM accuracy decrease with the decreasing motive nozzle inlet temperature.The HEM guarantee accurate results for operating regimes close to the CO2 critical point. AbstractIn this study, the accuracy of the homogeneous equilibrium (HEM) applied to 3-D CFD-based simulations of CO 2 expansion inside two-phase ejectors is presented. The HEM approach previously reported in the literature were assessed by comparing the computed and measured mass flow rates that pass through an ejector motive nozzle. In addition, the HEM approach implemented using CFD was tested over a vast range of ejector operating regimes. To ensure that all of the computations were performed consistently, a validated CFD model combined within an in-house developed script was used. The comparison of the experimental and computational results showed that the HEM accuracy varied for the different sets of operating parameters. Accurate results were obtained for operating regimes near or above the CO 2 critical point. The model accuracy decreased with the decreasing temperature and decreasing distance to the saturation line.

No abstract

No abstract

Highlights The modified homogeneous relaxation model of the R744 two-phase ejector was proposed. The application range of the proposed model is for a motive nozzle pressure above 59 bar. The proposed model improved the motive nozzle mass flow rate accuracy when compared to the homogeneous equilibrium model.

In this study, the accuracies of the homogeneous equilibrium (HEM) and homogeneous relaxation models (HRM) were compared. Both models were implemented in the ejectorPL computational tool. The HEM and HRM were used to simulate the carbon dioxide flow in ejectors that were designed for supermarket refrigeration systems. The model accuracy was evaluated by comparing the computational results with the experimental data. The discrepancy between the measured and computed motive nozzle mass flow rates was analysed. In addition, the difference between the experimental and computational mass entrainment ratios was calculated. The operating regimes in this study ranged from 47 bar to 94 bar and from 6 • C to 36 • C for the pressure and temperature, respectively. The model accuracy strongly depends on the distance between the operating regime and the critical point of the refrigerant. The discrepancy for the selected operating regimes ranged from 0.3% to 43.3% and 0.7% to 42.0% for HEM and HRM, respectively. For lower pressures and temperatures, the HRM has higher accuracy than the HEM. The errors of the HRM results were approx. 5% lower than those of the HEM results. The accuracy improvement of the HRM was considered unsatisfactory. The low accuracy improvements were possibly caused by the relaxation time formulation in the homogeneous relaxation model.