Eco-friendly plastic crystals take the gas out of refrigeration
Scientists at the University of Cambridge, UK, and the Universitat Politècnica de Catalunya and the Universitat de Barcelona, Spain, have developed a way to replace the organic gases used in most conventional refrigerators. By using crystals of neopentyl glycol under pressure, it may be possible to build safer, greener, and more efficient cooling systems.
The widespread use of refrigeration for both industrial and domestic purposes has revolutionized society by not only allowing food to be shipped worldwide and preserved for long periods of time, but – when used in air conditioning – making many regions of the Earth as comfortably habitable as any temperate area.
However, most conventional refrigeration devices rely on compression and expansion of gases to produce their cooling effect. It works, but gas refrigerators are energy-hungry, and the hydrofluorocarbons and hydrocarbons (HFCs and HCs) that are most commonly used are toxic, flammable, and are less than environmentally friendly.
"Refrigerators and air conditioners based on HFCs and HCs are also relatively inefficient," says Xavier Moya, a Royal Society Research Fellow in Cambridge's Department of Materials Science and Metallurgy. "That's important because refrigeration and air conditioning currently devour a fifth of the energy produced worldwide, and demand for cooling is only going up."
As an alternative, Moya and his team propose a solid-state refrigeration system. Instead of compressing and expanding gases, the new system uses solids – specifically, neopentyl glycol (NPG, 2,2-dimethylpropane-1,3-diol). This is an inexpensive organic compound widely used to synthesize polyesters, paints, lubricants and plasticizers. However, when NPG and similar crystals are placed under pressure by means of a magnetic field, an electric field or mechanical compression, the microscopic structure alters, producing a colossal barocaloric effect (CBCE).
In plain English, the crystals get very cold very fast.
It's an effect that is also seen memory alloys, but the team says that organic materials are easier to compress as well as cheaper. NPG has nearly spherical molecules that have loose bonds which rotate freely, making it easier to induce the barocaloric effect. It also makes NPG crystals plastic in the sense of being malleable rather than forming polymer chains.
According to the team, NPG produces unprecedentedly large thermal changes that are comparable to those seen in HFCs and HCs. Moya is currently working with Cambridge Enterprise, the commercialization arm of the University of Cambridge, to produce a marketable version of the technology.
The research was published in the journal Nature Communications.
Source: University of Cambridge