1. Model classification of compressor refrigeration oil: 1. Select lubricating oil according to different compression types; There are three kinds of compressors for freezers, namely, piston, screw and centrifugal. Piston and screw lubricating oil are in direct contact with refrigerant, so the interaction between them should be considered when selecting lubricating oil, while centrifugal lubricating oil is only used to lubricate rotor bearings, so N32 or N46 turbine oil can be selected according to load and speed. 2, according to the type of refrigerant to choose lubricating oil, which must take into account the interaction between lubricating oil and refrigerant. For example, refrigerants such as freon can be dissolved in mineral oil, so the viscosity of the selected lubricating oil is one level higher than that of the insoluble refrigerant, which ensures that the lubricating oil can be lubricated after dilution. In addition, we should also pay attention to the fact that a small amount of lubricating oil mixed with refrigerant will not affect the operation of the refrigeration system, and check whether the lubricating oil mixed with refrigerant precipitates wax crystals to block the refrigeration system, which is the quality index of the flocculation point of refrigeration oil that we often say. 3. In addition to selecting lubricating oil according to the type of refrigerant, lubricating oil can also be selected according to the evaporation temperature of refrigerant. Generally, the oil with corresponding freezing point is selected according to the evaporation temperature of refrigerant, and the freezing point of lubricating oil used in refrigerator with ammonia as refrigerant should be lower than the evaporation temperature. When freon is used as refrigerant, the freezing point of lubricating oil can be slightly higher than the evaporation temperature. 4. Different lubricating oils are selected for different working conditions of the refrigerator. Large and medium-sized multi-cylinder, high-speed (the average linear speed of piston is above 3m/s) and heavy-load refrigerators should use VG46 or VG68 or VG 100 refrigeration oil with high viscosity. VG68 or VG 100 refrigeration oil for high-load refrigerator with exhaust temperature around 145℃. Small, miniature or low-speed (average linear speed of piston is not higher than 2m/s) refrigerators can use VG22 or VG32 refrigeration oil. 2. Concept introduction: 1. The compressor is a fluid machine that lifts low-pressure gas into high-pressure gas, and it is the heart of refrigeration system. It sucks in low-temperature and low-pressure refrigerant gas from the suction pipe, drives the piston to compress it through motor operation, and then discharges high-temperature and high-pressure refrigerant gas from the exhaust pipe to provide power for the refrigeration cycle, thus realizing the refrigeration cycle of compression → condensation (heat release) → expansion → evaporation (heat absorption). 2. Refrigerator refers to the mechanical equipment that uses compressor to change the pressure change of refrigerant gas to realize low-temperature refrigeration. The compressor used is different from the general air compressor because its operating conditions and compressed working medium are different. According to the different structure and working principle, refrigerator is similar to air compressor, and can also be divided into several different forms, such as piston, screw and centrifugal. Refrigerator is one of the most important components in compression refrigeration equipment.