Elastocaloric cooling is a solid-state refrigeration method that uses shape-memory alloys to pump heat by mechanically stressing and unstressing the material. It works by exploiting a reversible phase change that releases heat when the alloy is loaded and absorbs heat when it is unloaded. A new compression-based prototype using NiTi tubes recently reached a heat-source temperature of −12 °C from a 24 °C heat sink, a 36 °C temperature lift, without greenhouse-gas refrigerants (Nature, 2026; IEEE Spectrum).
What is elastocaloric cooling?
Elastocaloric cooling is a form of solid-state cooling that replaces the vapor-compression refrigeration cycle with a mechanically driven heat-pumping cycle in a solid material. The most studied materials are shape-memory alloys such as nickel-titanium, often called NiTi or Nitinol.
The elastocaloric effect is a stress-driven phase transformation that causes a solid to heat up under loading and cool down under unloading, enabling a repeatable heat-pump cycle in a solid.
Because no high global warming potential gases are required, elastocaloric systems can, in principle, deliver high performance with a low environmental footprint.
How does elastocaloric cooling work?
The core mechanism is a stress-induced transition between austenite and martensite phases in the alloy. In a device, an array of NiTi tubes or wires is cyclically loaded in compression or tension while a heat-transfer fluid shuttles heat between a hot and a cold side.
- Loading step, heat out: apply mechanical stress, the alloy transforms and releases latent heat to a hot heat exchanger.
- Unloading step, heat in: remove stress, the reverse transformation absorbs heat, cooling the alloy below its starting temperature.
- Regeneration: an oscillating fluid flow through a porous or shell-and-tube regenerator stacks these small temperature changes into a larger temperature lift.
A widely studied configuration uses short NiTi tubes in compression arranged like a shell-and-tube heat exchanger, which prevents buckling and improves durability while allowing efficient cross-flow heat transfer. A 2022 regenerative device of this type achieved a 31.3 K span and more than 60 W heating or cooling power using only 13.7 g of alloy, with over 300,000 cycles without degradation (Joule, 2022).
How cold can elastocaloric cooling get?
Historically, many lab devices operated near room temperature because alloy transition temperatures and water-based fluids limited sub-zero operation. Two advances overcame this:
- Low-transition-temperature NiTi alloys that retain superelasticity down to roughly −20 °C
- Low-freezing-point heat-transfer fluids, for example aqueous calcium chloride brine
A desktop, compression-based, regenerative elastocaloric device using low-Af NiTi reached a heat-source temperature of −12 °C from a 24 °C heat sink, a 36 °C lift, demonstrating sub-zero performance without refrigerant gases (Nature, 2026).
These sub-zero results build on earlier records, including a 31.3 K temperature span and robust cycling in compression-loaded NiTi regenerators (Joule, 2022).
How efficient is elastocaloric cooling?
Device efficiency is reported using coefficient of performance, COP, and exergy efficiency, the fraction of the ideal Carnot limit achieved.
- Measured COP up to 5.2 in heat-pump mode at modest temperature span
- Exergy efficiency up to about 11 percent in heat-pump mode
- Specific heating or cooling powers of 3,700–4,400 W per kg of alloy at small spans
In a compression-loaded NiTi regenerator, COP values up to 5.2 and exergy efficiencies up to 11 percent were measured, with more than 60 W absolute power and linear power–span characteristics (Joule, 2022).
Further gains are expected with work-recovery schemes, lower-hysteresis alloys, optimized geometries, and higher operating frequencies. Unlike magnetocaloric systems, elastocaloric devices avoid rare-earth magnets, which simplifies cost and supply considerations.
Why is elastocaloric cooling important for climate?
Conventional vapor-compression refrigeration uses hydrofluorocarbon (HFC) refrigerants, which are potent greenhouse gases. Although sealed, leaks during manufacturing, servicing and end-of-life release HFCs to the atmosphere. Global cooling demand is already responsible for a large share of electricity use and emissions. Replacing gas refrigerants with solid-state refrigerants removes that direct climate risk while preserving high efficiency. Policy frameworks such as the Kigali Amendment target a global HFC phase-down, and eliminating them in new cooling technologies supports those goals. See overviews on sectoral emissions at Our World in Data and HFC markets from the UNEP Ozone Secretariat.
What are the limitations of elastocaloric cooling?
Key challenges remain before widespread deployment:
- Materials and hysteresis: NiTi alloys lose some input work to hysteresis, which lowers efficiency. Research targets lower-hysteresis, high-entropy-change alloys and microstructural tuning.
- Durability under load: Tension-loaded elements can fatigue, but compression-loaded NiTi tubes have shown hundreds of thousands to millions of cycles. Device design must prevent buckling while maintaining high heat-transfer area (Joule, 2022).
- System integration: Work recovery between out-of-phase regenerators, compact high-force actuators, and low-loss hydraulics are needed for commercial efficiency and cost.
- Low-temperature operation: Achieving freezing requires alloys with suitable transition temperatures and brines or other fluids that do not freeze, as demonstrated in the −12 °C study (Nature, 2026).
- Scaling power: Absolute power scales with alloy mass and frequency. Designs that increase mass without greatly increasing required force, for example longer regenerators with the same cross section, can raise output power.
Even with these caveats, recent sub-zero results and durable compression designs indicate a credible pathway to green, refrigerant-free cooling for refrigerators, heat pumps and vehicle thermal management.