A Second Law Study of the Regenerators in Cryocoolers based on Pore-level Analysis of Entropy Generation

Abstract

Regenerators are key components of regenerative cryocoolers and losses in regenerators have a significant effect on the performance of cryocoolers. In previous studies, the efficiency of regenerators has been characterized mostly based on the first law of thermodynamics, and second-law analyses have been based on exergy considerations or irreversibility associated with macroscopic flow models. In this work, we investigate the entropy generation in regenerators based on detailed pore-level simulations. Computational Fluid Dynamics (CFD) simulations are used to model two-dimensional regenerator geometries, and examine the microscopic flow and heat transfer phenomena that cause irreversibility. A CFD approach and a volume averaging semi-analytical approach are developed to analyze the entropy generation in pore level. A modified Bejan number (Re conv) and a Performance Evaluation Factor (PEF) are propose as indicators for the level of entropy generation in regenerators. The predicted entropy generation rates at various Reynolds numbers and geometric dimensions are analyzed. The results indicate that the proposed semi-analytical approach can be a convenient alternative to CFD simulations when empirical data of convective heat transfer and friction factor are available. The analysis of entropy generation using Reconv and PEF can be used to minimized the irreversibility of regenerators.