Elastocaloric cooling
Assembly Line
Eco-friendly cooling device with record-breaking efficiency
Researchers have developed an eco-friendly refrigeration device with record-breaking cooling performance in the world, setting to transform industries reliant on cooling and reduce global energy use. With a boost in efficiency of over 48%, the new elastocaloric cooling technology opens a promising avenue for accelerating the commercialization of this disruptive technology and addressing the environmental challenges associated with traditional cooling systems.
A New Way to Beat the Heat: Scientists Develop an ‘Elastocaloric’ Cooling Device
In search of an environmentally-friendly cooling solution, Dr. Ichiro Takeuchi, a materials scientist at the University of Maryland, and his research lab have developed an innovative “elastocaloric” cooling device made of nitinol—a nickel-titanium alloy—that does not rely on the use of harmful liquid refrigerants. Instead, nitinol tubes possess a unique physical property that allows the alloy to absorb heat, thereby cooling the area around it. This new device cools so effectively that it could be used in commercial refrigerators or air conditioners in the future. Widespread adoption of such a “caloric” cooling device would significantly diminish our dependence on environmentally harmful chemicals for cooling.
Caloric cooling devices are a class of newly developed materials that change temperature under certain conditions. For example, ‘magnetocaloric’ materials change temperature when placed in a magnetic field, and ‘electrocaloric’ materials change temperature when exposed to an electric field. Elastocaloric materials, on the other hand, respond to mechanical force, such as stretching or compressing, and absorb heat after the mechanical strain is released. These materials are non-volatile, meaning they do not easily evaporate into a gas. Therefore, their potential to contribute to global warming is, operationally, zero, making them extremely attractive candidates for alternative refrigeration.
A compact elastocaloric refrigerator
Elastocaloric cooling is regarded as one of the most promising cutting-edge alternatives to conventional vapor compression refrigeration systems. This technology is based on the temperature change of materials when being subjected to uniaxial stress, which has been observed in polymers, alloys, and ceramics. However, the existing elastocaloric prototypes have a bottleneck problem of an excessive mass ratio between the actuator and the solid-state refrigerant. To overcome this challenge, this study proposes an elastocaloric refrigerator using a single actuator with an inclined angle to produce a vertical tensile force to nickel-titanium (NiTi) shape-memory wires and a lateral motion to translate the NiTi wires between the hot and cold sides. The refrigerator can achieve a 90% improvement in the mass ratio between the solid-state refrigerant and actuator compared to the currently best-reported elastocaloric cooling prototype. The NiTi wires exhibit an adiabatic temperature change of 6.6 K during unloading at the strain of 4.8%. The proposed refrigerator can achieve a 9.2-K temperature span when the heat source and sink are insulated from ambient and has a cooling power up to 3.1 W under zero-temperature-span condition. By using thinner NiTi wires or NiTi plates, the developed elastocaloric refrigerator could be a starting point to promote applications of this technology in the future.
Materials, physics and systems for multicaloric cooling
Calls to minimize greenhouse gas emissions and demands for higher energy efficiency continue to drive research into alternative cooling and refrigeration technologies. The caloric effect is the reversible change in temperature and entropic states of a solid material subjected to one or more fields and can be exploited to achieve cooling. The field of caloric cooling has undergone a series of transformations over the past 50 years, bolstered by the advent of new materials and devices, and these developments have contributed to the emergence of multicalorics in the past decade. Multicaloric materials display one or more types of ferroic order that can give rise to multiple field-induced phase transitions that can enhance various aspects of caloric effects. These materials could open up new avenues for extracting heat and spearhead hitherto unknown technological applications. In this Review, we survey the emerging field of multicaloric cooling and explore state-of-the-art caloric materials and systems (devices) that are responsive to multiple fields. We present our vision of the future applications of multicaloric and caloric cooling and examine key factors that govern the overall system efficiency of the cooling devices.