People in the U.S. are turning up their air conditioning to beat the heat. These and other cooling devices use hydrofluorocarbons, which are potent greenhouse gases. Scientists reported a prototype device that could one day replace existing A/Cs. Solid Refrigerants are used to cool a space.
The results of the research will be presented at the fall meeting of the American Chemical Society.
"Just installing an air conditioner or throwing one away is a huge driver of global warming," said Adam Slavney, who is presenting this work at the meeting. Refrigerants used in these systems are thousands of times more potent than carbon dioxide and can accidentally leak out of systems when they are being handled.
Air conditioners cause a refrigerant to cycle between being a gas or a liquid. When the liquid becomes a gas, it expands and cools a room or the inside of a fridge. A compressor that works at 70– 150 pounds per square inch can turn gas into a liquid. The heat is directed outside the home by air conditioners. Concerns about climate change and stricter regulations on hydrofluorocarbons are driving the search for more eco-friendly ones.
It could be an ideal solution to use solid refrigerants. Solids will not leak from A/C units. Barocaloric materials are similar to gas-liquid cooling systems. The pressure drives a solid-to-solid phase change in this case. The internal structure of the material is different. The barocaloric solid materials have long, flexiblemolecular chains that are usually floppy and disorganized. The chains become more rigid under pressure. Jarad Mason, the project's principal investigator, says that the process of going from an ordered structure to a relaxed one is similar to melting wax. The material absorbs heat when the pressure is released.
Most barocaloric systems require a lot of pressure to drive heat cycles. The systems need specialized equipment that is impractical for real-world cooling applications. Barocaloric materials can act as cooling agents at lower pressures. They have shown that the metal-halide perovskites can work in a cooling system. According to Slavney, the materials we reported are able to cycle at about 3,000 psi, which is a lot of pressure.
A first-of-its-kind prototype has been built by the team to demonstrate the use of these new materials. There are three main parts. There is a metal tube with a liquid in it. There is a piece of the device that applies force to the liquid. The liquid helps carry heat through the system.
The team has shown that the barocaloric materials can turn pressure changes into full temperature changing cycles. Mason says that their system doesn't use pressures as low as commercial systems. This is the first working cooling system that uses solid-state refrigerants that rely on pressure changes.
A variety of barocaloric materials will be tested with the device now in hand. "We're hoping to use this machine as a testbed to help us find even better materials, including ones that work at lower pressures and that conduct heat better." Solid-state refrigerants could be a viable replacement for air conditioning and other cooling technologies if the material is optimal.
More information: Materials for practical solid-state barocaloric cooling: A chemist (re)invents an air conditioner, ACS Fall 2022. www.acs.org/content/acs/en/mee … tings/fall-2022.html
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