Eckhard A. Groll

Modeling of a Two-Stage Rotary Compressor

This paper presents the development and validation of a computer model for hermetic two-stage rotary compressors that can be used for design optimization. The model considers the effects of refrigerant leakage between the compressor chambers, heat transfer between the cylinder wall and the refrigerant gas, and heat loss by natural convection to the surroundings. The model numerically solves mass and energy balances for each of the compressors chambers to predict the pressure and temperature variations over a crankshaft revolution. The compressor power input and refrigerant mass flow rate are calculated and used to determine the isentropic and volumetric efficiencies. The model can operate both with and without intercooling between the stages to allow for study of the effects of intercooling on compressor performance. The model results are compared to the results of external performance tests that were conducted using a prototype compressor. The intermediate temperature and pressure, discharge temperature, power consumption, and mass flow rate were recorded for 17 different operating conditions. The model predicts the compressor power consumption and mass flow rate within ±5% of the experimental results.