Conifer-shaped multi-layer elastocaloric regenerators

Elastocaloric cooling enjoyed fast development, however, its full potential has yet to be released, partially due to the inevitable inhomogeneous phase transition in elastocaloric regenerators. Here, we report a conifer-shaped multi-layer elastocaloric regenerator by aligning geometry with variable transformation stress to address this challenge. Inspired by coniferous tree architecture, the design strategically varies the number of tubes across three layers to match the intrinsic transformation stress profile, mitigating overstress and incomplete transitions. Using identical commercial-grade NiTi material, the regenerator achieves a 45.5 K load-free temperature span that is 12.4% higher than the uniform baseline. Scalability is demonstrated via a reciprocating elastocaloric water chiller incorporating two regenerators, achieving 272.6 W cooling power at zero temperature span. We also demonstrate that the conifer shape applies to intra-layer, establishing a geometry-function matching principle for future high-performance elastocaloric regenerators and systems. Conventional wisdom in engineering design is uniform geometry. Here, elastocaloric regenerators with conifer-shaped geometry improve cooling performance because the stress gradient within matches the inevitable inhomogeneous temperature distribution.