Article by: Charles Fatima, on 06 July 2023, at 01:03 am PDT

Researchers from the University of Maryland and China have successfully developed an innovative elastocaloric cooling system that harnesses the heat-absorbing properties of metal tubes under tension. Led by Ichiro Takeuchi, the team achieved a cooling performance comparable to other caloric materials, opening doors for potential commercial use in the near future.

Traditionally, refrigeration systems rely on gases that have adverse environmental impacts due to their potent greenhouse effects when released into the atmosphere. To address this concern, scientists are exploring alternative solid-state refrigeration technologies based on caloric materials. These materials undergo temperature changes in response to external magnetic or electric fields, as well as mechanical stress or pressure. Apart from avoiding harmful chemicals, caloric-based cooling systems have the potential to be more energy-efficient than existing refrigerators.

While research has primarily focused on magnetocaloric materials, elastocaloric materials have emerged as even more promising candidates for commercial caloric cooling. One such material is nickel-titanium (NiTi), a highly elastic alloy that can be easily manufactured.

The team led by Takeuchi discovered over a decade ago that thin wires of NiTi can expel significant amounts of heat when subjected to tension and absorb it when the tension is released. Their journey to develop commercially viable cooling applications, however, encountered a significant technical hurdle. The repeated cycles of tension and release damaged the NiTi wires, limiting their practical lifespan.

To overcome this challenge, Takeuchi's team devised a novel heat exchange system that pumps water through bundles of NiTi tubes. Takeuchi explains, "It took us a long time to overcome various engineering challenges, but with our recent demonstration, we were able to realize what we envisioned a decade ago. We are utilizing water as a heat exchange fluid, making it colder so that it can be used for refrigeration or air conditioning purposes."

The team evaluated their approach based on two key metrics. The first is "delivered cooling power," which measures the rate of heat removal, while the second is the "temperature span," representing the temperature difference between the water at each end of the system. Takeuchi states, "We have achieved 260 W for delivered cooling power and 22.5 K for temperature span, respectively." By adjusting the operation sequences of valves in their heat-exchange system, the researchers maximized each of these values.

These recent advancements demonstrate how elastocaloric materials are rapidly catching up with the cooling performance of magnetocaloric counterparts, suggesting their potential as viable candidates for commercial cooling systems. Nevertheless, Takeuchi acknowledges that the practical utilization of elastocaloric materials may require the development of more advanced substances. He notes, "The high stress required for NiTi remains an obstacle, but there are other superelastic materials on the horizon that exhibit elastocaloric effects at much lower stress levels."

While these materials are still in the early stages of development and not commercially available, Takeuchi's team envisions their integration into low-stress cooling systems as an exciting prospect. They have already outlined plans for a compact elastocaloric wine cooler and aim to demonstrate a successful prototype once these advanced materials become accessible.

The findings were published in Science.