The compressor adjusts the cooling capacity by opening and stopping

Taking a household refrigerator as an example, when the refrigeration system is stably operated, the compressor attracts low temperature and low pressure gaseous working medium to become a high temperature and high pressure gas state after being compressed; the condenser is condensed into a normal temperature and high pressure liquid working medium; The capillary is throttled into a low-temperature, low-pressure vapor-liquid mixture into the evaporator; the working medium absorbs heat in the evaporator to cool the refrigerator, becomes a low-temperature, low-pressure gaseous working medium and is sucked into the compressor to complete the refrigeration cycle.

When the compressor is running, from the outlet of the capillary to the inlet section of the compressor, the working medium is in a low pressure state; while the working fluid flows out through the compression of the compressor, and the working fluid of the compressor outlet to the inlet section of the capillary is in a high pressure state. Therefore, when the system is in normal operation, the capillary divides the refrigeration system into a high pressure zone and a low pressure zone. When the temperature reaches the set requirement, the thermostat operates and shuts off the compressor circuit to stop the operation. At this time, since there is a pressure difference between the condenser and the evaporator, the liquid refrigerant will flow from the condenser (high pressure zone) to the evaporator (low pressure zone), and as the refrigerant flows, the entire system pressure gradually approaches equilibrium.

The way in which the compressor regulates the amount of cooling by opening and stopping, inevitably brings some problems to the refrigeration system. First, after the compressor is shut down, the refrigerant in the condenser flows into the evaporator due to the pressure difference. At this time, the working fluid in the evaporator will be more than the number of operating hours. When the compressor is started again, the first process is to move the excess working fluid in the evaporator to the condenser to redistribute the refrigerant in the refrigeration system. If the viscosity of the lubricating oil is too low or the amount of oil is too small, it will not form an oil film with sufficient strength, which will accelerate the wear of the machine. Conversely, if the viscosity is too high or the amount of oil is too much, the airtightness will be destroyed to cause leakage and reduce the productivity of the compressor. Therefore, it is necessary to select a lubricant of appropriate viscosity and control the amount of oil to be injected.