Design criteria of different heat exchangers for the optimal thermodynamic performance of regenerative refrigeration systems

Abstract

Heat exchanger effectiveness significantly influences the corresponding regenerative refrigeration system performance, a larger heat exchanger effectiveness, however, does not always lead to a better system performance. This study analyzes the optimal thermal conductances1 of each heat exchanger to explore their different effects and inherent relations on the optimal system performance. We first derive the theoretical relation between system requirements and design parameters, and then optimize the system by the Lagrange multiplier method, which directly gives the optimal solutions. By analyzing different variations of the optimal thermal conductances versus various system requirements and boundary conditions, the contributions of each heat exchanger to the whole system are explored. It is found that the hot-end heat exchanger is to transfer heat from refrigerant to external fluid, thus its thermal conductance should match the mass flow rate of external fluid. The cold-end heat exchanger is essential to accomplish heat transfer from environment to refrigerant, so it is dominated by the cooling requirements. In addition, the regenerator is to reduce the system pressure ratio and it always induces most irreversibility of the system, thus it depends on both the pressure ratio and other operating conditions significantly. The results above provide useful design criteria of heat transfer processes for regenerative refrigeration system optimization.