Application range of the HEM approach for CO2 expansion inside two-phase ejectors for supermarket refrigeration systems

Abstract

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.

Performance comparison of fixed- and controllable-geometry ejectors in a CO2 refrigeration system

“…In this study, the computations were performed using an HEM that has been extensively validated for a number of ejector geometries and operating conditions relevant to supermarket applications. As described in a study performed by Palacz et al (2015), the accuracy of this model for the prediction of the mass entrainment ratio was found to be very satisfactory. For transcritical and supercritical parameters, the discrepancies between the numerical and experimental results were below 10%.…”

“…This approach and a more advanced homogeneous relaxation method (HRM) have both been successfully implemented in the literature (Colarossi et al, 2012;Lucas et al, 2014;Yazdani et al, 2012). Recently, Palacz et al (2015) presented an extensive study on the accuracy of the HEM approach for the ejector technology used in supermarket refrigeration systems. In all of those simulations, the ejectorPL platform was used to analyse the considered cases in a controlled and systematic manner .…”

Thermodynamic Modelling of Supersonic Gas Ejector with Droplets

“…By assuming that the secondary choking pressure is uniform across L3 for both flows, the area occupied by the primary jet is calculated according to Equation (19):…”

“…The simplest choice is the Homogeneous Equilibrium Model (HEM), which assumes complete thermodynamic equilibrium between the phases. This model gives accurate results in the region close to and above the critical point [19]. Using this approach, Ameur et al [20] developed a model for determining the ejector flow properties in the context of Ejector Expansion Refrigeration Cycles, where the primary and secondary flows are, respectively, liquid and vapor and the entrainment ratio is indirectly fixed by the system through the quality at the outlet of the diffuser.…”

Performance improvement of the R744 two-phase ejector with an implemented suction nozzle bypass

“…According to the substantial developments of R744 ejectors, one of the most advanced numerical analysis investigations was delivered by (Palacz et al 2017), where full optimisation of ejector geometrical parameters was provided. A validated computational tool was used to simulate a transonic two-phase flow of the carbon dioxide trough ejector characteristic of the high pressure supermarket conditions (Palacz et al 2015;Smolka et al 2013). Six parameters describing the ejector shape were taken into the objective function of the optimisation procedure.…”