CH-24-C077 - An Experimental Study of Refrigerant Leakage in Variable Speed Rolling Piston Compressors

Many researchers have modeled the refrigerant’s internal flank leakage in rolling piston compressors as a convergent, divergent nozzle flow for simplicity in simulation work. To provide an accurate prediction, the mass flow rate of the isentropic nozzle flow was corrected by a flow coefficient, which was typically regressed from experimental data. In the rolling piston compressor, oil lubricant seals the clearance and improves the volumetric efficiency. The visualization experiments demonstrated that the oil-refrigerant mixture well sealed the clearance and showed a bubbly flow after passing the clearance. This phenomenon indicated that the refrigerant leakage comes from the solubility difference of the refrigerant in oil. Several researchers also proposed numerical approaches to simulate the leakage flow based on this phenomenon. Furthermore, there are barely any experimental works to support this idea. Our work studies the oil-refrigerant mixture leakage flow inside the variable-speed rolling piston compressor. The amount of mixture leakage caused by wall velocity and pressure difference could be evaluated by using the solubility difference and measured volumetric efficiency while adjusting the compressor's operating frequency at the same pressure ratio. The experimental results suggest that the mixture leakage caused by wall velocity is likely independent of the leakage by pressure difference. The leakage amount related to compressor speed has been identified by analyzing the mixtures at different compressor speeds. A mass flow rate prediction was improved from the 40% deviating manufacturer’s map prediction under lower evaporating temperatures to a 2% deviation.