Researchers at the Hong Kong University of Science and Technology (HKUST) have developed a low-cost refrigerant structure for solid-state cooling that survived more than 100 million operating cycles in tests. Inspired by honeycomb-like architectures, the design could help address two major barriers to elastocaloric refrigeration: manufacturing costs and mechanical durability.The structure uses thin sheets of nickel-titanium (NiTi), a shape-memory alloy, stamped into porous chips and stacked to form a tubular refrigerant unit. The team estimates it could last more than 10 years under the tested operating conditions.The findings, published in Science under the title “Stacked porous NiTi structure with low cost and ultrahigh fatigue life for elastocaloric cooling,” offer a potential route to producing elastocaloric cooling components at a scale and cost more suitable for commercial applications.How elastocaloric cooling worksConventional air conditioners and refrigerators generally use vapor-compression systems, which circulate refrigerants through a cycle of compression, condensation, expansion, and evaporation. These systems consume substantial energy, while some refrigerants can contribute significantly to global warming if released.Elastocaloric cooling takes a different approach. It uses shape-memory alloys that undergo reversible changes in their internal crystal structure when subjected to mechanical stress.When a suitable alloy is compressed or stretched, this transformation releases heat. Removing the stress reverses the process, allowing the material to absorb heat. Repeating this cycle, alongside a system that transfers heat in and out of the material, produces a cooling effect without conventional refrigerants.However, developing practical components remains challenging. They must withstand repeated mechanical loading while providing sufficient surface area for efficient heat exchange. Existing designs often rely on tubes, plates, and wires, or thin-walled components manufactured using wire-cut electrical discharge machining (WEDM). These approaches can be expensive and slow to produce, and some structures are vulnerable to fatigue damage.Stamping and stacking improves durabilityTo address these limitations, a research team led by HKUST professor Qingping Sun developed a technique called “stamping and stacking.”The process begins with commercial NiTi sheets, which are stamped into individual porous chips. These are then stacked to create a tubular refrigerant structure. Its layered architecture draws inspiration from the mechanical robustness of natural structures such as honeycombs and bamboo.The individual chips also help limit crack propagation. Instead of allowing a crack to travel along one continuous tube and potentially cause a major structural failure, the interfaces between adjacent layers can interrupt its spread.The manufacturing process offers a substantial cost advantage. HKUST says it can produce around 100 porous alloy chips per minute, making it more than 100 times faster and 95 percent less expensive than the WEDM method used for comparison.Tests showed that the structure could withstand more than 100 million operating cycles. Based on its performance under the tested conditions, the researchers estimate a service life of more than 10 years.A compact prototype demonstrates cooling potentialThe team incorporated the structure into an elastocaloric cooling prototype with a refrigerant unit measuring just 30 millimeters (1.2 inches) in length and containing 200 stacked NiTi chips.The prototype achieved a maximum temperature span of 11.7 kelvin (about 21°F) and a specific cooling power of 3.85 watts per gram. The temperature span represents the difference the system can establish between its hot and cold sides, rather than a room-temperature drop.The results demonstrate the potential of the design to combine compact dimensions with useful cooling performance. However, they do not establish the overall energy efficiency or operating costs of a complete commercial refrigeration system.The researchers plan to improve heat transfer, develop more energy-efficient actuation systems, and engineer higher-performance shape-memory alloys. The manufacturing method could also be adapted to thin alloy sheets processed through laser cutting or etching.The team has filed multiple international patents for the technology. While further development is needed before commercial deployment, the work offers a promising approach to making solid-state cooling components more durable and affordable.