Highly efficient grooved NiTi tube refrigerants for compressive elastocaloric cooling

Abstract

Elastocaloric (eC) cooling without environmental issues has been a promising substitute for the conventional vapor-compression refrigeration. Commercial superelastic NiTi shape memory alloy tubes show large elastocaloric cooling capacity and ultrahigh fatigue life under cyclic compression but suffer from the limited specific heat transfer area (Aht) and insufficient cooling performance. Up to now, compressive NiTi tube eC refrigerant with Aht larger than 1 m2 Kg−1 has not been available due to the easy buckling problem. In this work, the buckling-free vertically and spirally grooved NiTi tubes (VGT and SGT) with Aht of 1.04 m2 Kg−1 and 1.25 m2 Kg−1 respectively are developed as the compressive eC refrigerants. The VGT and SGT are fabricated by the slow-feeding wire electric discharge machining based on the bared NiTi tubes. Then a compressive eC refrigeration prototype (ERP) is built to experimentally characterize the specific cooling power (SCP) and system temperature span (ΔTspan) of the grooved tubes. Under the regenerative flow configuration, the VGT and SGT achieve large zero-ΔTspanSCP of 2.18 W g−1 and 2.61 W g−1 at the operation frequency (fERP) = 0.5 Hz. Besides, the VGT and SGT produce maximum no-cooling-load ΔTspan of 25.2 K and 27.7 K respectively at fERP = 0.417 Hz. The experimental SCP and ΔTspan exceed most of the reported eC regenerators and there are still rooms for enhancing the cooling results by improving the ERP in future. Overall, the developed VGT and SGT with large Aht records and excellent cooling performance show big potentials of heat transfer structure design in developing highly efficient eC devices.