The liquid refrigerant absorbs the heat of the cooled object in the evaporator, vaporizes it into low temperature and low pressure steam, is sucked by the compressor, compressed into high pressure high temperature steam and discharged into the condenser, and in the condenser to the cooling medium (water or air ) Exothermic, condensed into high-pressure liquid, the throttle valve throttling low-pressure low-temperature refrigerant, re-enter the evaporator heat absorption vaporization, to achieve the purpose of circulating cooling. In this way, the refrigerant in the system through the evaporation, compression, condensation, throttling four basic processes to complete a refrigeration cycle. In the refrigeration system, the evaporator, condenser, compressor and throttle valve is essential in the refrigeration system of four pieces, which is the evaporator is the cooling capacity of the equipment. The refrigerant absorbs the heat of the cooled object therein to achieve refrigeration. The compressor is the heart, plays the role of inhalation, compression, and delivery of refrigerant vapor. The condenser is a device that emits heat, passing the heat absorbed in the evaporator together with the heat transferred from the compressor work to the cooling medium. The throttle valve acts as a throttle to the refrigerant, and controls and regulates the amount of the refrigerant liquid flowing into the evaporator, and divides the system into two parts: the high pressure side and the low pressure side. In the actual refrigeration system, in addition to the above four pieces, there are often some auxiliary equipment, such as solenoid valves, distributors, dryers, heaters, fusible plugs, pressure controllers and other components, they are to improve the operation Economy, reliability and security.