Abstract
In this study, the homogenous relaxation model (HRM) for CO2 flow in a two-phase ejector was modified in order to increase the accuracy of the numerical simulations The two- phase flow model was implemented on the effective computational tool called ejectorPL for fully automated and systematic computations of various ejector shapes and operating conditions. The modification of the HRM was performed by a change of the relaxation time and the constants included in the relaxation time equation based on the experimental result under the operating conditions typical for the supermarket refrigeration system. The modified HRM was compared to the HEM results, which were performed based on the comparison of motive nozzle and suction nozzle mass flow rates.
Highlights
Due to the restrictive legal regulations for environmental protection in refrigeration, common synthetic refrigerants are replaced by the environmentally friendly natural refrigerants, such as carbon dioxide
The acceptable motive nozzle mass flow rate relative difference of the homogenous relaxation model (HRM) was reached for case #3, #4, #5, #6, and #7 for the relaxation time higher than 0.0001 s
The different constant relaxation time for whole vapour ejector was defined in order to evaluate the discrepancy difference of the motive nozzle mass flow rate and suction nozzle mass flow rate between different relaxation time
Summary
Due to the restrictive legal regulations for environmental protection in refrigeration, common synthetic refrigerants are replaced by the environmentally friendly natural refrigerants, such as carbon dioxide (denoted as R744). Prof Lorentzen patented a transcritical carbon dioxide system for automotive air conditioning, which led to the design and manufacturing of rival refrigeration systems with CO2 as the main working fluid [1]. One of the solution to improve the energy performance of the CO2 transcritical refrigeration cycle is the implementation of the two-phase ejector as the main expansion device in the cycle. Theoretical and experimental analyses have indicated that replacing the expansion valve with the ejector in the CO2 transcritical vapour compression cycle improves the energy performance [2]. The energy performance improvement of the R744 ejector expansion transcritical cycle up to 18.6% is indicated in [5].
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