Refrigeration is critical to modern society, and United Nations statistics show that between 25% and 30% of the world's electricity is used annually for refrigeration. Researchers from the Institute of Metal Research of the Chinese Academy of Sciences have found that plastic crystals (a type of disordered solid crystal that is easily deformed) have a squeezing effect, that is, a cooling effect caused by pressure, which can be used as a high-end refrigeration technology. New materials may reduce cooling energy consumption. This provides new ideas for the development of next-generation solid-state refrigeration technology. Related research results were published in the journal Nature on March 28. The plastic crystals reported in this research have the advantages of abundant raw materials, environmental friendliness and low energy consumption, and have broad application prospects in the field of refrigeration.
Most of the current refrigeration systems use gas compression refrigeration technology, but the materials used in this technology will have an adverse impact on the environment. Refrigeration technology based on solid phase phase change thermal effect has been widely concerned as a most promising alternative technology in recent decades. Moreover, it is estimated that the current refrigeration technology consumes about 25% to 30% of the world's electricity, so new refrigeration technologies are urgently needed.
Currently, a promising alternative is to use solid materials that produce temperature changes in response to external stimuli such as pressure. However, existing solid materials have always had the drawback of small energy changes, which limits their application potential.
The researchers found that a variety of plastic crystals can be greatly entropy-driven under very small pressures. One of the materials, called neopentyl glycol, produces entropy that is as high as 389 joules per kilogram, and the refrigeration capacity is higher than in the past. Phase change refrigeration materials have been greatly improved. This excellent property is attributed to the unique molecular structure of the plastic crystal: the plastic crystal is highly disordered, that is, the molecular orientation is irregularly arranged. This disordered structure is easily compressed, and relatively small pressures can induce regular alignment of these disordered molecules, resulting in large entropy changes.
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