Numerical Prediction of Refrigerant-Oil Two-Phase Flow from The Scroll Compressor Discharge to the Suction Side via the Back Pressure Chamber

Abstract

Оil lubricates the contact of the orbiting and stationary scroll in the refrigerant scroll compressor, while the sealing between the scrolls is achieved by the refrigerant vapour pressure in the sealed back pressure chamber. The back pressure should be adjusted by the refrigerant-oil two-phase flow from the oil separator at the compressor discharge to the back pressure chamber and the refrigerant-oil flow from the back pressure chamber to the compressor suction side. Both flows are conducted through connecting tubes with corresponding high-pressure and low-pressure nozzles of small diameters. Models for the prediction of refrigerant-oil critical and subcritical flows through nozzles are developed and applied for the prediction of back pressure. The models are original since the slip between oil and refrigerant as well as the refrigerant solubility in oil are taken into account. The critical flow model is validated against experimental data available in the literature. The back pressure is predicted by equating the mass flow rates of refrigerant and oil two-phase mixtures through the high and low-pressure nozzles. The results show that the critical flow takes place through the high-pressure nozzle, while the subcritical flow through the low-pressure nozzle can also exist in cases with small pressure difference between the back pressure chamber and the compressor suction side. The refrigerant solubility in oil has a small influence on the critical and subcritical refrigerant-oil mixture mass flow rates, while the influence on the back pressure is more pronounced.