Engineering: A cool new way to refrigerate

Plastic crystals may be a promising material for the development of new refrigeration technologies with reduced energy use and environmental impact, suggests a paper in Nature this week. Novel approaches to cooling are desirable, as current refrigeration technologies are estimated to consume around 25-30% of the world’s electricity.

Most conventional refrigeration systems use vapour compression to cool, but there is growing concern about the environmental impact of the materials used in this technology. Solid materials that show a change in temperature in response to an external stimulus, such as pressure, have been proposed as a promising alternative. However, the performance of existing solid-state materials has been limited to low energy changes (only tens of Joules per kilogram per kelvin, J kg-1 K-1), restricting their potential application.

Bing Li and colleagues demonstrate large pressure-driven thermal changes in a variety of plastic crystals. One of the tested materials, called neopentylglycol, produced energy changes of around 389 J kg-1 K-1. This substantial effect is attributed to the molecular structure of plastic crystals, which are highly disordered (that is, they do not have regular lattice formations). Relatively small pressures can induce large changes to these structures and therefore produce large energy changes. These materials require further optimization to improve their efficiency, the authors note, but they may offer a new route for exploring next-generation solid-state refrigeration technologies.