Applying position and time dependent nusselt number and friction factor into 1D model to improve regenerator design for solid-state caloric cooling cycles

Abstract

Active caloric regenerative cycles have recently attracted much attention as a promising cooling technology that can potentially replace the vapor compression cycle based on its high efficiency and eco-friendly characteristics. The use of modeling is necessary in optimizing the active caloric regenerative cycle due to the system’s complex structure and numerous parameters that need to be taken into account. The cycle uses oscillatory flow to efficiently exchange heat between the caloric material and the heat transfer fluid and to generate a desired temperature gradient in the regenerator. When the oscillatory flow is used, hydrodynamically and thermally developing regions occur all over the regenerator when the direction of the fluid flow changes.To the best of the authors’ knowledge, no previous research has considered the oscillatory developing regions in a 1D model. Therefore, this study incorporated the developing regions generated by the oscillatory flow as well as the entrance developing regions into a regenerator model for the first time. Based on the modeling results, the influence of the oscillatory developing regions and the average Nusselt number increase with higher cycle frequency. Additionally, the new 1D model produces average Nusselt number similar to the 2D model with a maximum error of 4 %. Considering that the 2D model requires very high computational cost to solve the transient condition of the caloric cycle, the advanced 1D model can accurately assess the performance of the caloric cycle and provide a detailed analysis of heat transfer phenomena and fluid dynamics in the regenerator at modest computational cost.The parallel plate type, optimized using the new model, has a hydraulic diameter of 0.1 mm. However, maintaining such a small space between the plates can be challenging from an application standpoint. Therefore, this study proposes the use of a wide rectangular microchannel matrix as the regenerator. The rectangular microchannel matrix, with an aspect ratio of 30, produces a coefficient of performance of 5.65, which is comparable to the parallel plate matrix. Consequently, the wide rectangular microchannel matrix can achieve both high Nusselt number and structural stability simultaneously.