Lubricating oil is also called refrigerating oil, which lubricates the moving parts of the compressor, not only reduces friction and wear, but also plays a cooling role, so that the moving parts keep a low temperature and improve efficiency. The influence of lubricating oil on refrigerant performance is mainly shown in the following aspects.
1. Thermodynamic performance, the oil dissolved into the refrigerant, the refrigerant thermal performance is reduced. At a certain condensing pressure, the pressure difference between evaporator and condenser increases, and the power consumption of compressor increases. In general, the evaporation temperature decreases by 1℃, to increase the power consumption of 4%. In addition, lubricating oil carrying refrigerant into the oil system will reduce the circulation of refrigerant in the system, resulting in a decline in refrigeration capacity.
2. Heat transfer effect Lubricating oil dissolved into refrigerant will cause the decrease of heat transfer coefficient. Pure refrigerants in the process of evaporation and condensation is boiling in heat and condensation heat transfer, the existence of oil will make heat exchange surface forming a layer of oil film, the heat transfer will be made by boiling way of heat transfer in heat and condensation heat transfer into oil and the coefficient of thermal conductivity is far less than that of boiling heat transfer coefficient and the condensation heat transfer coefficient, usually in oil 6%, will have a significant performance.
3. After the refrigerant enters the oil system, it fricts and heats up at the lubrication point. The refrigerant in the oil flashes due to the low boiling point, resulting in poor local cooling and excessive heating. It may flash in the thrust bearing to form the change of axial balance thrust, which causes the axial pulsation of the machinery and affects the sealing and bearing bearing capacity.
