The present paper is concerned with the study of the polytropic exponent of reciprocating hermetic compressors. The polytropic exponent finds application in the development of simpler simulation models for hermetic compressors. In such cases it is usually taken as a fixed input value. A previous study has shown that, for a given open reciprocating compressor, it remains fairly constant, even when the compressor is run with different refrigerants. In the present paper experimental data from hermetic reciprocating compressors have been analyzed to investigate the behavior of the polytropic exponent under different operating conditions. A mathematical model, based on mass, energy and momentum balance equations, and using data from standard calorimetric tests as input, was developed to determine the polytropic exponent. Results have shown that, for hermetic compressors, the assumption of a constant polytropic exponent is still valid.
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