Refrigeration and air conditioning technology has become an important subject in the development of science and technology in China. In recent years, refrigeration and air conditioning technology has been widely used in all fields of national economy and people's lives. For example, large and medium-sized cold storage, air conditioning of various civil and public buildings, commercial and household refrigerators, commercial freezers and so on. In order to adapt to the development and application of this special technology, many research institutions of refrigeration and air conditioning technology have been established recently. Many colleges and universities have added and strengthened the specialty of refrigeration and air conditioning technology. At the same time, the professional team engaged in the research, design, production and operation management of refrigeration and air conditioning technology is also expanding. Refrigeration equipment industry"Refrigeration" is to use certain methods to make an object or space reach a lower temperature than the surrounding environment medium within a certain period of time and maintain it within a given temperature range. The so-called environmental medium here is the air and water in nature. In order to make an object or space reach or maintain a certain low temperature, certain methods must be adopted to continuously take out the heat in the object or space and transport this heat to the external environment. According to the development of refrigeration technology, there are two methods of refrigeration: one is to use natural cold sources to refrigerate; Another is "artificial refrigeration". At present, "artificial refrigeration" is developing rapidly and being widely used.Natural cold sources include natural ice or deep well water stored in winter. Using the melting heat of natural ice and the heat absorption of deep well water with lower temperature than the ground, the object or space can be cooled to realize "refrigeration". Natural ice has the advantages of large storage and low price, and it is the earliest cold source used in ancient countries all over the world. As early as in The Book of Songs, China recorded that "two days of ice rushing, three days of ice falling in Lingyin", and in The Great Summer Fu, he also recorded a poem that "the ice accumulated in a secluded pavilion, and the air flew and became a book". These all describe the examples of our ancestors using ice to refrigerate food and prevent heatstroke and cool down, which shows that China has a long history of using natural cold sources to realize refrigeration. Because the use of natural cold source is limited by region, season and ice storage conditions, and the use of natural cold source is limited by refrigeration temperature range, it is difficult to meet the requirements of large refrigeration. Therefore, with the development and progress of artificial refrigeration technology, natural cold source refrigeration has gradually become artificial, and supermarket air curtain cabinets.Refrigeration also plays an important role in the production process of petrochemical industry. The liquefaction of natural gas and liquefied petroleum gas, gas separation and other processes are inseparable from refrigeration technology. The application of refrigeration technology in soil freezing provides safety guarantee and good economic benefits for mining and tunnel excavation.The application of refrigeration technology has promoted the production and development of medical and health products. The medical effect of some diseases. Low temperature provides a guarantee for the preservation and transplantation of biological organs. Development of cryobiology and bioengineering. Low-temperature medical treatment has effectively improved the awareness ofThe application of low temperature technology has further promoted