Numerical analysis for smaller entropy generation of micro-unit magnetic refrigerator at room temperature

Abstract

Magnetic refrigeration (MR) is earning global attention for being a promising alternative for vapor compression refrigeration, due to its characteristic of being energy efficient and environmentally benign. Currently, the widely accepted active magnetic regeneration refrigeration (AMRR) technology is facing some inherent problems caused by using heat transfer fluid, thus fully solid-state MR is proposed to avoid those problems. Micro-unit regeneration (MUR) magnetic refrigeration is a typical kind of it. To compare those MR systems from a perspective of energy utilization efficiency, we combine entropy generation theory with MR theory to establish a new performance evaluation standard of irreversible energy loss. And we constructed the numerical models of both AMR (parallel-plate) and MUR systems for entropy generation comparison analysis. The results show that micro-unit regeneration magnetic refrigeration system owns a smaller systematic entropy generation rate than the AMR system under the selected working conditions. When those two systems provide a temperature span of 8 K, the MUR system's entropy generation rate S˙MUR,tot is 52% smaller than AMR, thus, the performance of MUR system is better. Subsequently, the optimized condition for MUR system is found (for heat regeneration time tlattice=9s and the number of units Nunit=72), the largest temperature span is acquired exactly when S˙MUR,tot is the smallest. The results of MUR system's partial entropy generation rate show that entropy generation caused by heat transfer between MCM units from different heat regenerators takes 60% of S˙MUR,tot, which can provide theoretical guidance for the subsequent optimization for heat transfer enhancement.