A comparison of modeling paradigms for dynamic evaporator simulations with variable fluid phases

Abstract This paper provides a comparison of evaporator modeling techniques for dynamic vapor compression system simulations that can handle the appearance and disappearance of fluid phases in the heat exchanger using a fixed-step solver. This paper compares moving boundary models with different switching mechanisms as well as a finite control volume approach. Switching approaches include (1) enthalpy based switching which uses two-phase region length and evaporator outlet enthalpy as an event trigger, (2) void fraction based switching which includes the mean void fraction in the state variable vector, and (3) density based switching which uses two-phase region density to trigger mass conservative switching. Simulations are performed for three different refrigerants under three different operating conditions and results are compared through pressure, superheat, and air temperature outputs. The number of switches triggered during simulation are also presented for comparison. These results are used to provide recommendations for the minimum threshold length commonly used in these switching methods and also to highlight the advantages and disadvantages of each approach.

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