Innovative Heat-Driven Solid-State Refrigeration Using Shape Memory Alloys for Sustainable Cooling
A research team at the Karlsruhe Institute of Technology and the University of Tsukuba in Japan has unveiled a novel approach to refrigeration, leveraging residual heat and solar energy. This groundbreaking system employs two ultrathin shape memory alloy films that transform thermal energy directly into mechanical work, ultimately producing cooling effects.
Traditional refrigeration methods rely on electric-powered compressors which significantly contribute to global energy consumption, with cooling and heating now accounting for nearly half of worldwide energy use. Furthermore, common refrigerants exacerbate global warming, highlighting the need for alternative solutions. The new system offers a promising sustainable alternative by exploiting elastocaloric effects in solid-state systems that can operate without electric actuators.
At the core of this innovation are two nickel-titanium films with complementary functions. The first film responds to heat by contracting, converting thermal energy directly into mechanical work without the need for an electric motor. This motion is immediately transferred to the second film, which cyclically applies and releases mechanical load. These actions reversibly alter the films crystal structure, generating a cooling effect analogous to refrigeration.
According to Dr. Jingyuan Xu, head of the Young Investigators Group at the KITs Microstructure Thermal Laboratory, the key innovation is the combination of two functions within the shape memory alloys: one converts heat into mechanical work, while the other utilises that work to produce cooling. This approach opens new avenues for heat-based refrigeration, harnessing energy that is otherwise wasted, such as residual heat or solar thermal energy.
Initial laboratory tests with the proof-of-concept prototype demonstrated a temperature difference of 4 C at an actuator temperature of 86 C, while the elastocaloric refrigerant achieved nearly 13 C. These results confirm the feasibility of the system under realistic operating conditions. The prototype also operated reliably when supplied with external heat at 130 C, confirming that it can function with real-world heat sources. Yi-Ting Hsiau, the lead researcher, noted that measuring the cooling produced was a pivotal validation that the concept works outside theoretical models.
Although the current setup is conceived as a viability study and has not yet reached its maximum capacity, there are plans to connect multiple films in parallel to boost cooling performance. Potential applications include cooling processors in computers by using their own residual heat or cooling sensitive electronic components in electric vehicles by utilising waste heat from the transmission system. This technology represents a significant step towards sustainable, heat-driven refrigeration solutions that could reduce reliance on electrical energy and harmful refrigerants, particularly in sectors with high cooling demands.
Developed in collaboration with the University of Tsukuba, this innovative system paves the way for practical, energy-efficient refrigeration that could transform how cooling is achieved across various industries. As Xu emphasises, expanding this technology could lead to compact systems that utilise abundant heat sources, supporting sustainable cooling practices globally.