New study paves way to eco-friendly refrigeration

Chinese researchers have successfully tackled a long-standing challenge in refrigeration technology by discovering a novel method that promises low carbon emissions, high cooling capacity, and efficient heat transfer.

The study, published recently in the journal Nature, addresses the growing energy consumption and heat dissipation challenges that accompany the rapid development of computing power, a crucial component in the digital economy era.

Modern society relies heavily on refrigeration, from preserving food to cooling data centers. However, traditional vapor-compression cooling systems come with high electricity and environmental costs. In China, refrigeration technology accounts for about 2 percent of GDP while consuming nearly 20 percent of the nation's electricity and generating 7.8 percent of its carbon emissions.

Solid-state cooling has long been considered a cleaner alternative, as it avoids the use of fluorocarbon-based refrigerants that harm the environment. However, solid materials struggle with heat transfer efficiency, restricting their practical use in large-scale applications.

The research team, led by Li Bing, a professor at the Chinese Academy of Sciences' Institute of Metal Research, discovered a way to bypass this limitation by integrating solid cooling effects with liquid flow.

In their study of the salt ammonium thiocyanate — a widely-used non-toxic industrial material — the researchers observed that the salt's dissolution in water absorbs massive amounts of heat. By applying pressure, the process is reversed, causing the salt to precipitate and release a large amount of heat. This reversible cycle enables continuous cooling as pressure is alternately applied and released, making it an ideal mechanism for refrigeration systems.

"Unlike traditional solid-state cooling methods, where heat struggles to move across material boundaries, our approach integrates the refrigerant and heat-transfer medium into a single fluid, facilitating thermal conductivity and system integration," Li said. This approach solves what scientists described as the "impossible triangle" of caloric materials by delivering low emissions, high cooling power, and efficient heat transfer simultaneously.

Laboratory experiments demonstrated excellent results. At room temperature, the method achieved a temperature drop of nearly 30 C in just 20 seconds, while at higher temperatures the cooling span reached as high as 54 C, far exceeding that of existing solid-state caloric materials.

In a designated prototype cooling cycle, simulations suggest a cooling capacity of 67 joules per gram and an efficiency approaching 77 percent, demonstrating potential for engineering applications. Moreover, in-situ spectroscopic experiments proved the process' stability, reversibility, and instant response to pressure changes — key requirements for practical refrigeration systems.

"This technology transcends traditional refrigeration principles based on various phase transitions. By turning the 'coolant' into a fluid that can be pumped directly through heat exchangers, it paves the way for the commercialization of powerful, zero-emission refrigeration systems for industrial and home use," Li said.

"It could inspire the expansion of this principle to other chemistries, enabling the development of tailored caloric properties suitable for a variety of temperature ranges and cooling capacities," he said. "However, further efforts are needed for practical application, such as breakthroughs in engineering rapid and reversible pressure-tuned phase transitions."

He emphasized that the technology's excellent high-temperature performance makes it "an ideal candidate for the demanding thermal management requirements of next-generation artificial intelligence computing centers".