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HEM and HRM accuracy comparison for the simulation of CO2 expansion in two-phase ejectors for supermarket refrigeration systems

Abstract

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.
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Category

Academic article

Client

  • Research Council of Norway (RCN) / 196445
  • Research Council of Norway (RCN) / 244009

Language

English

Author(s)

  • Michal Palacz
  • Michal Haida
  • Jacek Smolka
  • Andrzej J. Nowak
  • Krzysztof Banasiak
  • Armin Hafner

Affiliation

  • Silesian University of Technology
  • SINTEF Energy Research / Termisk energi
  • Norwegian University of Science and Technology

Year

2017

Published in

Applied Thermal Engineering

ISSN

1359-4311

Publisher

Elsevier

Volume

115

Page(s)

160 - 169

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