Development of a Film-Based Elastocaloric Cooling Device

Elastocaloric cooling is a new emerging solid-state technology with the potential to provide environmentally friendly cooling with high efficiency. Superelastic shape memory alloys films are especially promising for elastocaloric cooling, since they combine a high elastocaloric effect size with highly efficient heat transfer due to the large surface-to-volume ratio of film geometries. In the present work, we investigate thermomechanical characterization of ultra-low fatigue TiNiCuCo films and evaluate performance at an elastocaloric cooling device with out-of-plane loading. Firstly, two film designs are addressed with different transition regions for stress homogenization. The design criteria include control of phase transformation kinetics, release/absorption of latent heat, and compromise of thermo-mechanical performance and overall film size governing temperature change and cooling capacity, respectively. Secondly, digital image correlation and finite element method simulation of phase transformation kinetics at the meso-scale are performed to understand mechanical and thermal local response of the films including band formation and evolution, tilt angle as well as strain-rate dependence. Then, the elastocaloric effect at the material level is evaluated for the two film designs, including temperature span, adiabatic limit, coefficient of performance and lifetime. Finally, a test device is developed considering ultra-low fatigue TiNiCuCo films, enhanced heat transfers and adaptable SMA fixtures, and its cooling performance at the device level are studied. In this study, we present a strategy involving optimized mechanical fixations and loading mechanisms, alongside enhanced thermal contact, with the aim of maintaining the ultra-high cyclic stability of TiNiCuCo films at the device level.