Suxin Qian

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.

Refrigeration is indispensable to modern society¹, yet the dominant vapour-compression systems rely on environmentally harmful fluorocarbon refrigerants with high global warming potential^2,3,4. Solid-state caloric refrigeration offers a low-carbon alternative^5,6,7, but its practical deployment has been hindered by limited cooling capacity and the inefficient indirect heat transfer that requires secondary fluids. Here we report an extreme barocaloric effect in NH₄SCN aqueous solutions enabled by pressure-tuned dissolution and precipitation. This mechanism delivers an exceptionally large cooling capacity and markedly enhanced cooling efficiency. We obtain an in situ temperature drop of 26.8 K in the solution at room temperature, surpassing all known caloric materials. A Carnot-like cycle is designed to deliver 67 J g⁻¹ cooling capacity per cycle with a second-law efficiency of 77%, benefiting from the extremely large temperature drops and direct heat transfer due to the self-circulating aqueous solution. Beyond the phase-transition scenario, this dissolution-based approach that combines the merits of current leading technologies emerges as a promising sustainable refrigeration solution.

Elastocaloric cooling offers a solid-state alternative to conventional vapor-compression systems by leveraging stress-induced phase transitions in materials like shape-memory alloys (SMAs). This review comprehensively analyses the development and performance of elastocaloric cooling systems to date. We explain the thermodynamic mechanisms and material requirements, emphasizing challenges such as low latent heat and fatigue life. Subsequently, we categorize and compare thermal contact and heat-transfer-fluid (HTF)-based prototypes, discussing their achievements in temperature span and cooling power. The technical maturity of elastocaloric cooling systems is not comparable to commercial vapor-compression systems yet in terms of coefficient of performance (COP) and practicality. We further explore innovative approaches like work recovery, modular design, and novel loading modes (e.g., torsion) to bridge application gaps. The review concludes that elastocaloric cooling holds promise for sustainable refrigeration, though material fatigue, system COP, and heat transfer efficiency remain critical bottlenecks for future research.

Elastocaloric cooling is considered a leading alternative to traditional vapor-compression refrigeration. While current research has primarily focused on room-temperature applications, elastocaloric technology holds significant potential for low-temperature solid-state refrigeration. This study develops the first elastocaloric refrigerator operating below −60 °C. The refrigerator features a compact design driven by a single power source that manages the loading and unloading of shape memory alloy ribbon. A synchronized linkage mechanism regulates contact between the ribbon and the heat source/sink, facilitating efficient solid–solid contact heat transfer. By employing a TiNiCuNb quaternary alloy specifically designed for low-temperature superelasticity and elastocaloric response, with the ambient environment precooled from room temperature to −60 °C in an environmental simulation chamber, the system achieves a temperature span of 8.5 K under adiabatic conditions and a pull-down temperature of 4.8 K when rejecting heat at −60 °C, with a maximum cooling power of 5.9 W at zero temperature span. These mechanical innovations demonstrate the viability of elastocaloric cooling at low temperatures, offering valuable insights for future advancements in elastocaloric refrigeration technology.

Directional liquid transport (DLT) is essential for water harvesting, thermal management, and biomedical systems. Temperature-responsive structures offer a promising route for adaptive DLT control. However, fully passive and reversible shape transformation with effective directionality remains challenging. Here, we present a temperature-responsive valve (TRV) that converts thermal stimuli into uni-directional liquid transport via automatic mechanical deformation. The proposed unit is a shape memory alloy (SMA) slice embedded within an elastic tube lined with internal fin arrays. Upon heating, the curvature of SMA slice increases. Thus, the fin array beneath is compressed into an asymmetric configuration that generates driving force for stable uni-directional liquid transport. It operates across a wide wettability range of liquid, and supports modular configurations for multifunctional integration. We introduce key applications including reconfigurable direction switching, multimode mixing, and thermal patterning. The system achieves to transport ~ 3000 µL liquid volume over ~ 66 mm, which outperforms the existing DLT systems of thermal stimuli. These performances originate from augmented Laplace pressure difference, reverse pinning, and asymmetric wetting structure. This work establishes a scalable framework of reconfigurable DLT control, offering new opportunities for intelligent microfluidic systems.