Effect of inactive section on cooling performance of compressive elastocaloric refrigeration prototype

Abstract

Elastocaloric (eC) cooling using shape memory alloy (SMA) with zero direct carbon emission is a promising alternative of traditional vapor-compression technology. Compressive eC refrigeration prototype (ERP) performs high fatigue life but suffers from the limited cooling performance. Many studies focus on enhancing the heat transfer property of compressive eC regenerators to improve the specific cooling power (SCP). However, reducing the SCP loss is also essential for developing high-cooling-performance compressive ERPs but has not been given sufficient attention. In this study, we revealed that the force holder widely used in compressive ERPs works as an inactive section that dramatically reduce the SCP produced by the NiTi SMA active section. Numerical heat transfer simulations and experiments were conducted to study the impact of the inactive section on the SCP at varied operation parameters. Nondimensionalized governing equations of the numerical model revealed that the volume ratio (Volnon) of the fluid channel of the inactive section to that of the active section is the determinant geometric parameter for the SCP decrease. Numerical results show that, larger operation frequency fERP, smaller dimensionless fluid velocity V* and system temperature span (∆Tspan) lead to more pronounced decreases in SCPnon (ratio of the SCP to ideal SCPideal at Volnon = 0) as the Volnon increases. It also indicates that the Volnon should be minimized to better < 0.08 for achieving excellent SCPnon > 0.95. Experiments validate that the regenerator with a reduced Volnon = 0.08 exhibits a notable increase of 30.8% and 66.7% in zero-∆TspanSCP and no-load ∆Tspan respectively, in comparison to the regenerator with Volnon = 0.5. Therefore, minimizing the Volnon of the inactive section via reducing the length and diameter of the fluid channel inside the force holder is necessary and highly recommended for developing high-performance compressive ERPs.