Computer Aided Design Studies of a Multiple Cylinder Refrigeration Compressor

Abstract

A multi-cylinder refrigerant compressor was analytically modeled and simulated on a digital computer. The modeling includes the kinematics of the mechanical compressor, the thermodynamic processes in the cylinders and the flow process of the refrigerant gas in and out of the cylinders. In addition the modeling includes the valve dynamics in controlling the gas flow, the thermodynamic processes in the common suction and discharge plenums and the interaction of the cylinder processes through the common plenums. The remainder of the refrigeration system was treated as pressure-temperature drop. The analytical model was compared to experimental data in terms of cylinder pressures, suction-discharge plenum pressures and temperatures, valve motions and the average mass flow rate of the refrigerant gas. The correlation between the comparison variable was quite good with some error in the prediction of suction valve closing time. The analytical model was used to predict the effect of increased compressor speed on the performance of the compressor. The speed was increased from 500 rpm to 2700 rpm with a decrease in volumetric efficiency from 87 percent to 60 percent, an increase in mass flow rate from 0.0378 kg/s to 0.151 kg/s. Valve impact speeds were also calculated to predict degradation in valve life.