Hong Kong developers boost elastocaloric efficiency

HONG KONG: Researchers in Hong Kong claim to have developed an elastocaloric cooling device capable of achieving a record-breaking temperature lift of 75K.

Solid-state elastocaloric refrigeration based on latent heat in the cyclic phase transition of shape memory alloys (SMAs) could provide an environmentally friendly alternative to traditional vapour compression refrigeration technology. However, the relatively small temperature lift between 20K and 50K, which is a critical performance indicator of the cooling device’s ability to transfer heat from a low-temperature source to a high-temperature sink, has hindered the commercialisation of this emerging technology.

Researchers at the School of Engineering of the Hong Kong University of Science and Technology (HKUST) have developed a multi-material cascading elastocaloric cooling device made of nickel-titanium (NiTi) shape memory alloys, boosting efficiency by over 48%.

The research team led by Prof Sun Qingping and Prof Yao Shuhuai from the Department of Mechanical and Aerospace Engineering selected three NiTi alloys with different phase transition temperatures to operate at the cold end, intermediate end, and hot end, respectively. 

By matching the working temperatures of each unit with the corresponding phase transition temperatures, the overall device’s superelastic temperature window was expanded to over 100K and each NiTi unit operated within its optimal temperature range, significantly enhancing the cooling efficiency. 

The built multi-material cascading elastocaloric cooling device achieved a temperature lift of 75K on the water side, surpassing the previous world record of 50.6K. 

The research team now plans to further develop high-performance shape memory alloys and devices for sub-zero elastocaloric cooling and high-temperature heat pump applications.