Enhancing cooling performance of NiTi elastocaloric tube refrigerant via internal grooving

Abstract

• A grooved NiTi tube is designed and fabricated as the elastocaloric refrigerant. • A buckling-prevention frame is developed to ensure uniform compression of the tube. • Compared with ungrooved one, the grooved tube has 53% larger SCP (1.30 W g −1 ). • With the buckling-prevention frame, the grooved tube endures 2 million cycles. Developing novel heat transfer surface structure on NiTi shape memory alloy tubes has big potential to enhance the elastocaloric cooling performance. In this work, an internally grooved superelastic NiTi tube (outer diameter 5 mm, wall thickness 1 mm and length 50 mm) is designed and fabricated as the refrigerant in a compressive regenerative elastocaloric cooling prototype. The geometric parameters of the longitudinal grooves (groove width, groove depth, and groove spacing) are optimized by a numerical heat transfer simulation. A buckling-prevention frame is developed to ensure uniform compression of the NiTi tube in the cooling prototype. Compared with the ungrooved tube of the same size, the specific internal heat transfer area of the grooved NiTi tube (3.44 mm −1 ) is increased by 360%, producing 53% larger specific cooling power (1.30 W g −1 ) and 33% larger maximum system temperature lift (8 K). With the buckling-prevention frame, the grooved NiTi tube endures 2 million reversible phase transition cycles under the compressive stress of 800 MPa in the prototype. Such significantly enhanced cooling power of the grooved NiTi tube with high fatigue life demonstrates the critical roles of heat transfer surface structure and buckling prevention in enhancing the elastocaloric cooling performance under compression.