Invaluable to modern society, refrigeration faces challenges from traditional vapor-compression systems, which are energy-intensive and employ refrigerants that exacerbate the greenhouse effect and damage the ozone layer. Addressing this, a research team from The Hong Kong University of Science and Technology (HKUST) has unveiled the world’s first zero-degradation elastocaloric cooling device. Powered by a fatigue-resistant, solid-state refrigerant, this innovation delivers durable and green cooling, maintaining its stable performance even over a stunning one million operational cycles. This breakthrough will usher in highly efficient eco-friendly cooling, driving progress towards sustainable global development.
Elastocaloric cooling, which is based on the reversible stress-induced phase transformation of shape memory alloys (SMAs), offers a promising green alternative to traditional refrigeration. Despite its great potential, commercialization has been impeded by performance degradation and low reliability. The prevalent use of commercial NiTi SMA as the refrigerant in most existing elastocaloric cooling devices is a key challenge. This material is prone to functional fatigue, causing its cooling power to decline over extended use.
To overcome this bottleneck, a team led by Prof. SUN Qingping, Chair Professor in the Department of Mechanical and Aerospace Engineering at HKUST, has developed a fatigue-resistant SMA and integrated it into an innovative refrigerant structure. By combining advanced SMA materials with device-level design and engineering, they have successfully addressed the critical issues of material functional fatigue and structural reliability. The breakthrough has resulted in a zero-degradation elastocaloric cooling device capable of maintaining stable cooling performance over long-term operation, characterized by the following distinct features:
(1) Fatigue-Resistant Shape Memory Alloy: A new quaternary TiNiCuCo alloy was engineered. Compared with traditional NiTi alloys, this material provides stable elastocaloric performance throughout numerous cyclic phase transitions. Its consistent release and absorption of latent heat are key to its function as a dependable solid-state refrigerant, crucial for the device’s sustained cooling capabilities.
(2) Mechanically Reliable Refrigerant Structure: A double-layer fin-type refrigerant structure was designed and fabricated to enhance both heat transfer efficiency and buckling resistance, achieving an ultra-high fatigue life exceeding 10 million cyclic compressive cycles.
(3) Compact and Durable Device Architecture: The device architecture was optimized to reduce thermal losses and improve system stability. This innovative design achieved a 50% reduction in components and reduced the proportion of ineffective parts from 15% to 5%.
Utilizing this novel material and device design, the research team constructed a novel elastocaloric cooling device integrated with multiple refrigerant units. This device achieved a constant cooling power of 400W and maintained a constant temperature span of 41K (a temperature difference of 41°C) over one million operation cycles without degradation. Accelerated fatigue testing of the TiNiCuCo refrigerant also showed no functional degradation after 100 million cycles. Under real-world cooling conditions, the refrigerant is expected to operate reliably for more than a decade.
Prof. SUN Qingping, corresponding author of the paper, stated, “While significant progress has been made in cooling performance over the past decade, long-term cooling stability is crucial for practical deployment. By integrating advanced shape memory alloy materials with innovative device engineering, we have tackled this key challenge. This breakthrough in cooling stability, achieved at both the material and device levels, brings the technology one step closer to real-world applications beyond laboratory demonstrations. We are currently developing an air-conditioner based on this technology. Moving forward, we aim to further enhance energy efficiency, power density, and cost competitiveness of elastocaloric refrigeration systems to accelerate their market adoption as a sustainable cooling solution.”
Dr. LIN Hongyang, a Postdoctoral Fellow in the Department of Mechanical and Aerospace Engineering at HKUST, is the co-corresponding author of this study. PhD student LI Yang is the first author. Contributing alongside them were Postdoctoral Fellow Dr. LI Xueshi, and PhD students SU Changfeng and HU Jiyuan. The findings have been published in Joule, a leading academic journal in the energy field, under the title “A zero-degradation elastocaloric cooling device using fatigue-resistant refrigerant”.
