Abstract: The oil superheat is currently adopted as the criterion of the reliability for rotary compressors in air-conditioning systems. It is generally acknowledged that the viscosity of the oil increases monotonously with oil superheat. Experimentally studied the relationship between the solubility characteristics of refrigerant in oil, the oil superheat and the oil viscosity. The results showed that the dissolved refrigerant levels were almost the same at various positions within the oil pool, and the saturation state was not reached. Therefore, the oil viscosity in positions with high temperature was rather low, and for a fixed position within the oil pool, the oil viscosity could decrease when the superheat raised in some testing conditions, which indicated that viscosity is not monotonously related with oil superheat. The experiment results proved the limitation and irrationality of the current methodology which utilized oil superheat as a standard for compressor reliability, to a certain extent. It is also recommended to use oil viscosity as a more reasonable criterion.

Key words: Compressor, Oil superheat, Viscosity, Solubility, Experimental study