Bubble-wall interactions in a vertical gas-liquid flow: bouncing, sliding and bubble deformations

The paper presents results of a study on the motion of bubbles rising in upward shear liquid flow in the vicinity of a vertical wall. Bubbles were found to slide along the wall, when their diameter is small. Bubbles could also experience multiple collisions with the wall at certain experimental parameters (geometry of a channel, range of superficial liquid velocity, bubble size, etc). The latter was theoretically predicted by solving the equation of the bubble motion for the lateral direction in the boundary layer of the channel. For this, the available in the literature constitutive models for the interfacial forces acting on a bubble in the vicinity of the wall were used. A simplified 1D model predicting bubble lateral displacement near the wall and taking into account the balance of drag and non-drag forces acting on a bubble was proposed. The numerical results were verified against the experimental ones obtained by non-intrusive high-speed video observations and subsequent image processing.
The experiments on the bubble motion were conducted in a vertical acrylic duct having a square cross-section of 25 cm2 and a height of approximately 1.3 m. Desalinated water and air both taken at the room temperature were used in the experiments. All measurements on the bubble motion were performed at channel heights between 0.8 and 1 m above the gas injection point.