Modeling of Leakage Through Small Clearances in a Hermetic Rotary Compressor

Leakage is an important factor in compressor energy efficiency. Flow through small clearances is a large fraction of the overall mass flow in small hermetic compressors, and an understanding of its mechanism is important. In this paper the leakage in a hermetic rolling piston compressor is modeled as the flow of lubricating oil with dissolved gas. The internal leakage gaps are modeled as channel flow. The model calculates the leak rate as the geometry dependent gap size changes. The thermodynamic relation for the solubility of refrigerant in oil is used to determine the refrigerant leak rate as a percentage of the oil leak rate. Compressor calorimeter tests are used to verify how compressor modifications affect the leak rate. Good agreement has been found between the experimental and theoretical model. The model can assist in determining optimum compressor geometry parameters, such as bore and stroke, that will minimize leakage. Also there is an indication that oil with a low refrigerant miscibility will reduce internal leakage losses. It is shown that additional research is needed to improve methods of direct measurements of leakage and to better characterize the nature of the mass transfer process.