New Barocaloric Cooling Technique Promises Greener Refrigeration

A groundbreaking cooling technique developed by researchers from the Institute of Metal Research at the Chinese Academy of Sciences offers a promising, environmentally friendly alternative to traditional refrigeration. This innovative method, based on dissolution barocaloric cooling, achieves a cooling capacity of 67 J/g and an efficiency of nearly 77%, enabling a temperature reduction of 27 K in just 20 seconds.

Traditional refrigeration methods largely rely on vapour-compression technology, a process that has been utilized since the 19th century. This approach involves a liquid refrigerant evaporating into a gas, absorbing heat from its environment, and subsequently being converted back into a liquid by a compressor. While effective, this system is energy-intensive and has reached near its maximum efficiency limits, as defined by the Carnot limit. Furthermore, the refrigerants used often have harmful environmental effects.

Revolutionizing Cooling with Barocaloric Techniques

In recent years, researchers have shifted attention toward caloric cooling, which manipulates entropy within materials through various means, including mechanical forces and applied pressure. Among these techniques, barocaloric cooling stands out as particularly promising. Yet, many existing barocaloric materials are solid, leading to slow heat transfer and limited cooling capacity.

The new system overcomes these limitations by utilizing a fundamental thermodynamic process known as endothermic dissolution. This process occurs when a salt is dissolved in a solvent; it requires energy, resulting in a temperature drop. A team led by metallurgist and materials scientist Bing Li discovered a way to reverse this cooling process by applying pressure. They specifically used the salt ammonium thiocyanate (NH4SCN) dissolved in water.

By applying pressure to the solution, the salt precipitates out, an exothermic reaction that aligns with Le Chatelier’s principle. Upon releasing the pressure, the salt re-dissolves almost instantaneously, resulting in a significant temperature drop of nearly 27 K at room temperature and up to 54 K at higher temperatures.

The choice of ammonium thiocyanate is strategic; it acts as a chaotropic agent, disrupting hydrogen bonding and enhancing solubility in water. Its sizable enthalpy of solution further contributes to the dramatic cooling effect. Notably, it demonstrates a high sensitivity to pressure levels in the range of hundreds of megapascals, making it compatible with standard hydraulic systems.

Applications and Future Prospects

According to Li, the technique detailed in the journal Nature could pave the way for similar non-phase transition cooling methods. The use of aqueous NH4SCN barocaloric cooling is particularly suited for high-temperature applications, such as thermal management in AI data centres. Other potential applications include air conditioning systems for vehicles and buildings.

Despite its promise, several challenges must be addressed before this technology can be commercialized. The corrosive nature of NH4SCN poses risks to refrigerator components, and the high pressures needed in the current system could lead to long-term damage. To tackle these issues, the research team plans to investigate other near-saturated solutions at the atomic level, focusing on their responses to pressure.

“Such fundamental studies are vital if we are to optimize the performance of these fluids as refrigerants,” Li stated.

This research represents a significant step toward more sustainable refrigeration technologies, potentially reshaping the landscape of cooling solutions for various industries. As interest in environmentally friendly technologies continues to grow, the barocaloric cooling technique could play a crucial role in meeting future energy efficiency demands.