Better Solid Refrigerants Beckon

June 3, 2019
Researchers achieved pressure-driven thermal changes at near room temperature using malleable plastic crystals.

A breakthrough in refrigeration science by researchers in the U.K. and Spain promises to revolutionize the way the chemical industry carries out its expensive cooling processes. The team, at Cambridge University, Cambridge, U.K., Universitat Politècnica de Catalunya, Barcelona, Spain, and Universitat de Barcelona, Barcelona, achieved pressure-driven thermal changes — or barocaloric (BC) effects — at near room temperature that they call colossal and an order of magnitude better than those observed in any other BC materials.

At the heart of the breakthrough are highly malleable plastic crystals (PCs), also known as orientationally disordered crystals, which lie at the boundary between solids and liquids. This malleability allows PCs to undergo huge pressure-driven thermal changes as a result of molecular reconfigurations.

In this case, the researchers worked with commercially available samples of the PC neopentylglycol (NPG), which is made from cheap abundant elements and already widely used by the chemical industry in the synthesis of paints, lubricants and cosmetics. As the PCs of NPG transition to an ordered crystal structure under the applied pressure, they yield what the researchers describe as an enormous latent heat.

The temperature change achieved is comparable to that observed in standard commercial refrigerant R134a and other hydrofluorocarbons (HFCs) and hydrocarbons (HCs), the researchers say.

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“Refrigerators and air conditioners based on HFCs and HCs are also relatively inefficient,” notes Xavier Moya, a Royal Society Research fellow in Cambridge’s department of materials science and metallurgy. Moya is also a leader in the field of solid refrigerant research.

Moya believes the demonstration of colossal BC effects in commercially available PCs should immediately open avenues for the development of safe and environmentally friendly solid-state refrigerants.

Following the filing of a priority patent application, Moya now is working with Cambridge Enterprise, the commercialization arm of the university, to obtain funding to develop demonstrations of the technology.

“We are now crossing the so-called ‘valley of death’ which stretches between promising materials and a working prototype ready for industry adoption. We are currently assessing the feasibility of developing an efficient barocaloric cooling cycle for light commercial refrigeration applications while providing zero greenhouse warming potential,” notes Jennie Flint, senior commercialization associate at Cambridge Enterprise. The work already has attracted industrial interest from several sectors — demonstrating both the industry pull and the potential breadth of applications of the technology, she adds. “Industry collaboration is key to incorporating our barocaloric materials into future cooling devices,” Flint stresses.

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