Pressure Makes Best Cooling - Dr. Kuo Li

MARCH 28， 2019 

New study from an international research team of scientists co-authored by Dr. Kuo Li from HPSTAR found that a class of disordered materials, called plastic crystals, exhibit record-large barocaloric effects under very weak pressure. The study reveals that the plastic crystals are the most promising materials for green cooling applications. The study is published in the recent issue of journal Nature.

Cooling is common and very important in our daily life—for example, food storage and air conditioning—and about 25 per cent of the world’s electricity are consumed for cooling.

Current cooling technology mostly uses the conventional vapour compression cycle. While the materials used in this technology have growing environmental probles because of their large global warming potential.

Cooling induced from the barocaloric effect— refers to cooling effects produced in a material by the application of pressure— is a promising green technology in efficient, economic and environment for cooling.

For barocaloric effect, a parameter called entropy change is always used to evaluate a material for the cooling applications. “For real application, it is desirable for a material to have larger entropy changes while induced by smaller pressure”, said Prof. Bing Li, the lead author of the study from Institute of Metal Research, Chinese Academy of Sciences.

Their neutron scattering and synchrotron X-ray diffraction techniques revealed that the intrinsically disordered structure, high compressibility and anharmonic lattice dynamics in the plastic crystals contribute to the record value of entropy change. It represents a milestone in this field of study.

Caption: Schematic diagram of the refrigeration cycle based on barocaloric effects.

制冷技术在当今社会工农业生产、日常生活等多个领域均起到了至关重要的作用，联合国统计数据表明全球每年25-30%的电力被用于各种各样的制冷应用。而这些应用绝大部分依赖传统的气体压缩制冷技术，普遍使用对环境和人体有害的制冷剂。因此，寻求绿色、环保、低能耗的替代制冷方案已经成为学术界和工业界共同努力的方向。近年来，基于固态相变热效应（caloric effects）的固态制冷技术被认为是最有希望取代传统气体压缩制冷的技术方案。固态相变热效中的压卡效应是一种由于压力诱导晶体结构相变而导致的制冷效应。固态相变制冷材料的性能主要由等温熵变所描述—高的等温熵变对应好的制冷效应。北京高压科学研究中心的李阔研究员参与的研究团队在一系列称为塑晶（plastic crystals）的有机材料里发现了基于分子取向序的压卡效应。 该材料的等温熵变较传统固态相变制冷材料高出了一个数量级。在塑晶体系中，所需驱动压力极低，且材料十分廉价，具有诱人的应用前景。相关研究发表于近日的《自然》。