HKUST NiTi cooling structure withstands over 100 million cycles in tests
HKUST engineers stamped and stacked porous NiTi chips into an elastocaloric refrigerant structure; a lab prototype reached an 11.7 K temperature span.
A team at the Hong Kong University of Science and Technology (HKUST), led by Prof. Sun Qingping, has built a porous nickel-titanium (NiTi) refrigerant structure for elastocaloric cooling that operated for more than 100 million cycles, according to hkust.edu.hk. The work was published in Science under the title "Stacked porous NiTi structure with low cost and ultrahigh fatigue life for elastocaloric cooling" hkust.edu.hk
hkust.edu.hkhkust.edu.hkOpen source ↗. The authors estimate a service life of over 10 years under the tested operating conditions.
Elastocaloric cooling absorbs and releases heat through the reversible phase transformation of shape memory alloys (SMAs), and it is considered a solid-state alternative to vapor-compression refrigeration. The latter is energy-intensive, and its refrigerants can contribute to the greenhouse effect.
Stamping and stacking method
Existing SMA refrigerant structures rely on commercial tubes, plates and wires, or on thin-walled parts made by wire-cut electrical discharge machining (WEDM). According to the authors, these approaches are costly, slow, and prone to fatigue failure and buckling under repeated loading.
The HKUST team instead stamps commercial SMA thin sheets into porous chips and stacks them into a tubular refrigerant structure. The design draws on the stacked porous architecture of honeycombs and on bamboo hkust.edu.hk
hkust.edu.hkhkust.edu.hkOpen source ↗. The stamping process produces 100 chips per minute, which the authors say is more than 100 times faster and 95% cheaper than WEDM.
Durability and prototype results
The structure is assembled from individual chips rather than a single long tube. The interfaces between adjacent chips help arrest crack propagation and prevent catastrophic longitudinal splitting. In tests, the structure withstood more than 100 million operating cycles.
Using a 30-mm-long refrigerant unit with 200 stacked chips, the team built an elastocaloric cooling prototype. It reached a maximum temperature span of 11.7 K and a specific cooling power of 3.85 W g⁻¹.
The authors note that similar structures could be made from thin SMA sheets produced by laser cutting or etching hkust.edu.hk
hkust.edu.hkhkust.edu.hkOpen source ↗. The team's next steps are improving heat-transfer performance, developing more energy-efficient actuation systems, and engineering higher-performance SMAs. First author of the paper is PhD student Su Changfeng; PhD students Li Yang and Hu Jiyuan also contributed.
