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.