Miscibility of Refrigeration Oil and Refrigerant
The refrigerating oil is highly miscible with the refrigerant and enters the condenser and the evaporator with the refrigerant. Therefore, the refrigerating oil has to lubricate and cool the moving parts without adversely affecting the refrigeration system. The physical, chemical and thermal properties of the frozen oil should meet the following requirements:
(1) Appropriate viscosity: The viscosity is too large, the flow resistance is large, the frictional power consumption and starting resistance of the compressor will increase; the viscosity is too small, the lubricant film is not easily formed, and the sealing property is also affected.
(2) the cloud point is lower than the evaporation temperature;
u Cloud point: Traces of paraffin remain in the frozen oil. When the temperature drops to a certain value, the paraffin begins to precipitate. The temperature at this time is called the cloud point.
(3) The freezing point is sufficiently low; (the freezing point of the R22 system is below 55 degrees below zero)
u Freezing point: the temperature at which the frozen oil loses fluidity
(4) The flash point is high enough: 20-30 degrees higher than the compressed exhaust gas temperature.
u Flash point: the lowest temperature at which flash oil vaporizes when in contact with flame
(5) Good chemical stability: low acid value
(6) Low impurity content: 1kg of frozen oil should contain less than 40mg of water and no mechanical impurities;
(7) Good insulation performance: the breakdown voltage is required to be above 25kV.