Article Source: New Scientist
A fridge that runs on plastic crystals could solve a big problem: our need to stay cool is warming the planet.
Refrigeration equipment, air conditioners, and heat pumps are estimated to consume between 25 and 30 percent of the world’s electricity – and many rely on greenhouse gases to transfer heat.
Bing Li at the Chinese Academy of Sciences’ Institute of Metal Research in Shenyang and his colleagues have used an alternative cooling material known as plastic crystals, which they believe could use less energy and be better for the environment.
Conventional fridges rely on compressing a material so it changes from gas to liquid. The liquid absorbs heat from its surroundings, in this case the inside of the fridge, causing it to turn back into a gas and beginning the cycle anew.
These refrigerant materials are fluids that absorb and release heat efficiently but are problematic because they contribute to global warming.
One type, chlorofluorocarbons (CFCs), are known to deplete the ozone layer and have been mostly phased out, but their more ozone-friendly replacement, hydrofluorocarbons (HFCs), are also powerful greenhouse gases.
Developed countries began reducing HFCs this year, but exactly what chemicals refrigerators and air conditioners will use instead is still unclear – carbon dioxide has been considered as a possible replacement.
Solids that change temperature in response to external pressure have been floated as greener alternatives. Plastic crystals, soft and mouldable solids with a powder-like appearance, were created decades ago and have been used in a range of products, including cosmetics, paints, and plastics.
Some have been considered as a material to store energy, but Li and his colleagues found that they work surprisingly well as a refrigerant.
Plastic crystals have a disordered structure, says Li, meaning they don’t have a regular lattice formation. “A tiny pressure can switch the materials between the disordered state and the ordered state,” says Li, resulting in a large change in energy.
One type of plastic crystal, neopentylglycol, has an energy change tens of times greater than other potential solid refrigerants, meaning it has a far greater cooling effect on its surroundings when the same pressure is applied.
“We identified plastic crystals as promising materials for solid-state refrigeration,” says Li, but the team needs to do more work to reduce heat loss and maximize the energy efficiency of the process in order to match that of existing liquid-to-gas refrigerants.