Exploration of refrigerant vapor-lubricating oil two-phase flow in a scroll compressor

Precise information about the oil discharge rate (ODR) of a compressor and the oil retention rate (ORR) in the oil sump is essential for compressor design, development, and operation. An extended two-fluid model (E-TFM) is developed to study the complicated refrigerant vapor-lubricating oil two-phase flow inside a compressor. Gas-liquid bubbly, droplet, and well-mixed flows are defined on the local cell scale in the E-TFM. Numerical simulations are conducted to investigate the oil-vapor flow field and predict the ODR and ORR of a scroll compressor. The ODR predictions given by the volume-of-fluid method, the conventional Euler-Euler model, and the E-TFM are compared and validated against available measured data. The results confirm the reliability and applicability of the E-TFM. Most oil droplets escaping from the discharge pipe are found to originate from the newly generated droplets via stripping and breakage of the down-flowing thin oil film in the middle cavity. The droplet diameter significantly influences the predicted ODR, whereas the termination criterion for gas-liquid bubbly flow has little effect on the predicted ODR or flow field over the range considered in this study. To improve the ODR prediction performance of E-TFM, efforts should be made to implement a population balance equation to capture the droplet size.