Performance of a semi-hermetic reciprocating compressor with propane and mineral oil

The experimental performance of a semi-hermetic reciprocating compressor working with propane as the refrigerant is reported in the present paper. Tests have been performed both with and without an internal heat exchanger between the vapour suction line and the liquid line, at different settings of the expansion valve. The suction vapour superheating is shown to improve volumetric efficiency and, therefore, global compression efficiency. Experimental results are discussed and explained by means of the high solubility of propane in the mineral oil used as the lubricant, which can cause an excessive reduction of the refrigeranteoil mixture viscosity at low suction superheating. Besides, the possibility of condensation on a cold spot inside the cylinder has also been considered. A modified version of the empirical model by Pierre (1982) for the prediction of volumetric and global compression efficiencies is proposed for propane.