Modeling of Graded Active Magnetic Regenerator for Room-Temperature, Energy-Efficient Refrigeration

It has been demonstrated experimentally that grading the regenerator along the flow direction with multiple magnetocaloric materials (MCMs) with varying Curie temperatures improves the performance of magnetic refrigeration significantly. The optimization of the graded active magnetic regenerator (AMR) is a multiphysics problem, which is crucial to the realization of room-temperature magnetic refrigeration. Until now, only a few models have been built and further work to understand the grading effects is urgently needed. In addition to the challenges of the coupling of magnetic, heat transfer and fluid dynamic phenomena and the vast parameter space of the graded regenerator (e.g. composition and geometry), relevant material properties of the MCMs may not yet be available for modeling. To address these issues, a COMSOL model with key material properties estimated by the mean field theory and the de Gennes model has been built. In this paper, two-segment regenerators composed of GdxTb(1 - x) alloys are studied first. Compared to a pure Gd regenerator, it is demonstrated that a two-segment one can achieve a > 3-time increase in cooling capacity. Furthermore, the temperature profile of a graded regenerator, which can be estimated using a first-order approximation, is found to correlate strongly with the cooling capacity, and could potentially serve as an index for performance prediction. The finding is applied to the study of three-segment regenerators. It is demonstrated that three-segment regenerators can cool a space faster and achieve cooling capacities higher than these of two-segment ones, especially for large temperature spans.