In a medium temperature application, the major resistance to heat transfer in the evaporator is the film of refrigerant oil. How may this be reduced?

In a medium temperature application, the major resistance to heat transfer in the evaporator can be attributed to the film of refrigerant oil that forms on the heat transfer surfaces. By adjusting the superheat within the system, the refrigerant’s temperature can be optimized, which helps to improve the heat exchange process.

When superheat is adjusted, it influences the temperature of the refrigerant as it leaves the evaporator. By maintaining optimal superheat, you ensure that the refrigerant is vaporized sufficiently before entering the compressor, thus promoting efficient heat transfer. This process can reduce the thermal resistance presented by the oil film, allowing for better heat transfer with the refrigerant.

This is especially important because excessive oil film can hinder the overall efficiency of the evaporator, leading to lower system performance. Properly managing superheat allows the system to effectively counteract the insulating effect of the oil film, enhancing the heat transfer efficiency within the evaporator.