Reduced dimensions elastocaloric materials: A route towards miniaturized refrigeration

Elastocaloric cooling technology has obtained huge attraction over vapor compression systems because it is more efficient with negligible environmental impact. The elastocaloric effect (eCE) is generally concerned with superelasticity and latent heat of shape memory alloys (SMAs), related to the martensitic transformation (MT) under uniaxial loading/unloading. There are various small-scale applications such as microelectromechanical systems, medical devices and lab-on-chip systems, where active local cooling with precise temperature control is essential for their proper functioning. To explore potential eCE for miniaturized active refrigeration, reduced dimensions SMAs (i.e. thin films, microwires, ribbons and foams) may be attractive for micro cooling devices by providing a large surface to volume ratio and thus high heat transfer capacity, low thermal hysteresis and high working frequency. Therefore, the eCE properties of the state-of-the-art reduced dimensions elastocaloric materials (eCMs) are thoroughly reviewed and comparatively discussed with their bulk counterparts. The most appropriate eCMs for miniaturized eCE refrigeration are revealed on the basis of large adiabatic temperature change (△T_ad), low stress hysteresis (△σ_hys), high cyclic stability and large coefficient of performance of material (COP_mat). The challenges and recent achievements for micro cooling eCE devices/prototypes based on small-sized eCMs are summarized.