Plastic crystals could replace greenhouse gases used in refrigerators

A team of chemical engineers at Deakin University, working with colleagues from the University of Western Australia, the University of Sydney and Monash University, all in Australia, has found that a type of plastic crystal can be used as a refrigerant, possibly replacing the greenhouse gas currently used in most refrigerators.

Their study is published in the journal Science. Josep-Lluís Tamarit and Pol Lloveras, with Universitat Politècnica de Catalunya, in Spain, have published a Perspectives piece in the same journal issue, outlining the work.

The most commonly used gas in modern refrigerators is R-134a, a hydrofluorocarbon that has largely replaced freon. And while it does not contribute to the breakdown of the Earth’s ozone layer, it is a greenhouse gas and thus, as it leaks from refrigerators, contributes to global warming. In this new effort, the researchers have found a possible replacement—one that is not even a gas.

The idea involves the use of “plastic crystals”—so named because once they are grown, their molecules can move under certain conditions. Prior research had shown that when pressurized, the molecules in organic ionic crystals move from a disorganized state to a neat grid configuration. When pressure is released, the molecules return to their disorganized state. More importantly, when they are pressed into an organized state, the crystals absorb heat, which chills the air around them.

In their work, the researchers tested several types of such crystals to find one that viably chills the air around it when compressed at ambient temperatures. They found several that were capable of pulling heat from the air at temperatures ranging from -37°C to 10°C.

To use the crystals as a refrigerant, the researchers built a compression chamber to squeeze the crystals and added a fan to blow the chilled air into the area around the device. By repeatedly squeezing and un-squeezing the crystals, the researchers found they functioned as a clean refrigerant. They acknowledge that more work is required due to the extreme amount of pressure needed to squeeze the crystals, making it an expensive way to cool a home.

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