EXERGY-BASED FIGURE OF MERIT FOR REGENERATIVE AND RECUPERATIVE HEAT EXCHANGERS WITH APPLICATION TO MULTISTAGE CRYOCOOLERS

摘要

One of the major losses in cryogenic refrigerators operating on oscillating regenerative cycles or steady state recuperative cycles is due to regenerative or recuperative heat exchangers in the cycles, respectively. Accurate numerical modeling of these losses requires extensive numerical simulation of coupled mass, energy, and momentum conservation equations. In this study, a unified model based on exergy flow is developed to define the Figure of Merit (FOM) for heat exchangers with application to multistage cryogenic refrigerators. It is shown that the conventional definition of exergetic efficiency used for heat exchangers is not convenient for their performance evaluation in their application to multistage cryocoolers. It is shown that a rational definition of exergy input to the heat exchanger component is necessary for proper definition of the FOM. The result of the first order model of the regenerator is compared to the results of computational fluid dynamics using REGEN 3.2. The effect of intermediate cooling on the FOM of recuperative heat exchangers is presented. The exergy destruction in the heat exchangers due to heat transfer and fluid flow are presented and discussed.