The era of burning power to fight heat may finally be coming to an end. Researchers at the Germany’s Karlsruhe Institute of Technology (KIT) and Japan’s University of Tsukuba have introduced the “world’s first” heat-driven, elastocaloric solid-state cooling system.
Interestingly, the system doesn’t require electric motors and runs directly on ambient warmth, waste heat, or sunlight. It links two ultra-thin nickel-titanium (NiTi) shape-memory alloy films to eliminate the need for an electric motor.
“The crucial innovation is that we combine two complementary functions of shape memory alloys, with one film converting heat into mechanical work and the other film converting this work into cold,” explained Dr. Jingyuan Xu, who leads the Young Investigator Group of the ZEco Thermal Lab at KIT’s Institute of Microstructure Technology (IMT).
“This way, we’re establishing a new approach to drive solid-state cooling, thereby opening up exciting possibilities for the use of waste heat and solar energy,” Xu added.
Two film structures
Cooling and heating consume nearly half of global energy. Meanwhile, chemical refrigerants continue to leak into the atmosphere, worsening the climate crisis.
Early models of solid-state “elastocaloric” materials offered a greener path because these alloys cool down when stretched and released. However, those early systems still used electricity to drive the mechanical force.
The new approach removes the plug altogether by pairing two paper-thin nickel-titanium films that work in tandem.
The first film acts as the system’s internal engine. When exposed to warmth, this shape-memory alloy contracts sharply, converting thermal energy directly into a powerful mechanical pulling force without needing an electric motor. This mechanical action instantly stretches the second film, acting as the refrigerator. As the load releases, reversible structural shifts within the metal drop its temperature drastically, generating cold air directly from heat.
The system utilizes a 22-micrometer one-way shape-memory alloy actuator film paired with a 26.5-micrometer superelastic alloy refrigerant film. The mini actuator foil generates a high force-to-displacement ratio of 14.5 N/mm — outperforming comparable commercial electromechanical actuators by more than ten times.
Shows promise in testing
In initial experiments, the prototype successfully proved its practical feasibility by delivering a 4°C (39 F) component-level temperature drop and nearly 13°C (55 F) of cooling in the elastocaloric material using an 86°C (186 F) actuator input. The system also demonstrated robust real-world capabilities by operating reliably when powered by external heat sources reaching up to 130°C.
“The decisive moment for us was when we were able to measure the cold that had indeed been generated by a heat-driven system. This showed us that the principle doesn’t just work in theory,” said Yi-Ting Hsiau, lead author of the study and doctoral researcher at the IMT.
According to the study, elastocaloric cooling is far more efficient than existing compact technologies. It can reach up to 84 percent of its maximum theoretical cooling efficiency, leaving other thermoelectric cooling modules far behind.
Although current prototypes serve as early feasibility models, researchers are actively scaling the system’s cooling output by connecting multiple alloy films in parallel. Future practical applications include using processor exhaust heat to self-cool computer chips and repurposing drivetrain heat to cool automotive electronics.
High-performance computer chips could soon use their own exhaust heat to stay cool. Electric vehicles could chill their sensitive cabin electronics using thermal waste from the drivetrain.