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制冷就是使某一空间内物体的温度低于周围环境温度并能维持这个低温的过程。制冷及低温技术有着十分重要的应用,关系到国计民生的多个重要领域,如食品储藏、航空航天、医疗卫生、科学试验等。根据制冷产生的低温环境的不同,制冷技术大体分为三类,120K以上至环境温度以下为普通制冷,20-120K为深度制冷,OK以上至20K为低温和超低温制冷。早期制冷主要采用气体膨胀的方式来获取越来越低的低温,到1932年,荷兰人克西姆采用降低液氦压力的方法获得了0.7K的最低温度。这几乎达到了气体膨胀制冷的极限。因此促使人们探索新的方法以获取更低的温度。
Refrigeration is the process by which the temperature of an object in a space is below the ambient temperature and maintained at this low temperature. Refrigeration and cryogenic technology have very important applications, related to the many important areas of national economy and the people’s livelihood, such as food storage, aerospace, medical and health, scientific experiments. According to the different low-temperature environment, the refrigeration technology can be divided into three categories, 120K above the ambient temperature for ordinary refrigeration, 20-120K for deep cooling, OK above 20K for low temperature and ultra-low temperature refrigeration. Early cooling mainly used gas expansion method to get lower and lower temperatures. By 1932, Kösch got the lowest temperature of 0.7 K with the method of reducing the pressure of liquid helium. This almost reached the limit of gas expansion refrigeration. Thus prompting people to explore new ways to get lower temperatures.