The thermodynamics, heat transer and fluid mechanics role of lubricant oil in hermetic reciprocating compressors

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The present paper reviews recent developments on the influence of oil on several thermophysical phenomena in reciprocating compressors. Besides the more essential role of lubrication, the oil is responsible for several tasks in the compressor, from cooling to keeping a low system pressure while the compressor is idle. Thermodynamics dictates the amount of dissolved refrigerant the oil can retain at a particular condition. Hence, the viscosity of the lubricant is directly affected by the refrigerant solubility in the oil. Heat transfer is crucial for keeping a low temperature in the compressor because thermodynamic losses increase with increasing gas temperature. Fluid mechanics is essential to guarantee that oil is delivered to the bearings and that lubrication is performed efficiently under any operating condition.