Abstract:
In the global energy consumption structure, heating and cooling demand accounts for nearly half of energy consumption, and this demand continues to rise. For more than a century, traditional refrigerators, air conditioners and data center cooling systems have relied almost exclusively on electrically driven compressors and flowing refrigerants to transfer heat. Many traditional refrigerants are also greenhouse gases that contribute to global warming.
Today, a research team from the Karlsruhe Institute of Technology (KIT) in Germany and the University of Tsukuba in Japan has made a major breakthrough and successfully developed the world's first prototype of a solid-state refrigeration system driven entirely by thermal energy, realizing a new technical route that gets rid of electric motors and directly converts waste heat or solar energy into cold energy.
This system overcomes the key bottleneck of "Elastocaloric Cooling", a cutting-edge solid-state refrigeration technology. As a promising alternative to traditional compression refrigeration, shape memory alloys cool when the applied mechanical load is released; however, prior to this, existing elastomeric refrigeration systems still relied on electrically driven actuators to provide mechanical external force, which prevented the technology from directly utilizing readily available waste heat or solar energy from the surroundings.
The joint team's new design revolutionizes this power mechanism, replacing traditional electric actuators with "thermal energy" itself. The core of the system lies in the ingenious combination of two ultra-thin nickel-titanium shape memory alloy films with different divisions of labor: the first film acts as a thermal actuator, shrinking using the shape memory effect when heated, and directly converting thermal energy into mechanical work without the need for a motor; this displacement motion then acts on the second film that plays a refrigeration role. By periodically loading and unloading it, it triggers reversible changes in the crystal structure of the material, thereby continuously generating cold energy.
The research project is led by Dr. Jingyuan Xu, head of the young research team of ZEco Thermal Energy Laboratory of KIT Institute of Microstructure Technology (IMT). He pointed out that the key innovation of this breakthrough is to combine two complementary functions of the shape memory alloy - one film is responsible for converting heat energy into mechanical work, and the other film converts mechanical work into cold energy. This design establishes a new solid-state refrigeration drive paradigm, opening up promising possibilities for efficient utilization of waste heat and solar energy.
Experimental data shows that the prototype device successfully demonstrated measurable cooling effects in laboratory tests. When the actuator is at a temperature of 86 degrees Celsius, a temperature difference of 4 degrees Celsius is achieved at the entire component level, while the temperature change of the elastic refrigerant itself is close to 13 degrees Celsius. In addition, the researchers introduced an external heat source of 130 degrees Celsius to test it, and the system also maintained stable and reliable operation, fully proving the feasibility of the technology to match the heat source in a real industrial environment. Yi-Ting Hsiau, the first author of the paper and a doctoral researcher at KIT, said that being able to measure the cold energy actually produced by the thermal drive system with one's own eyes is a very decisive moment, which confirms that the theoretical principle is by no means just a piece of paper.
The prototype device currently manufactured is mainly used for concept verification and feasibility demonstration, and has not yet been optimized for maximum cooling capacity. The research team is currently trying to exponentially increase the overall cooling capacity of the system by extending multiple layers of films in parallel. As the technology gradually matures and becomes miniaturized, its future application scenarios are very broad: computer processors or server units can "use the waste heat they emit to cool themselves." The waste heat generated by the automotive powertrain can also be directly converted into a cooling power source for sensitive automotive electronic components. The scientific research team stated that this achievement is only the beginning. In the future, with the expansion of the system and the implementation of compact design, the massive amount of environmental waste heat that can be seen everywhere will be expected to be converted into green and sustainable refrigeration resources.
Comments