The Effect of Wettability on a Large Bubble Rising in an Inclined Circular Pipe Filled with Water

Abstract

Observation has been made on the behavior of a single large bubble rising in an inclined circular pipe filled with water. The inner wall of the pipe is wetted by water. It is coated with fluororesin to get it to be poorly wetted. In the inclined poorly wetted pipe, the rising velocity of a single bubble increases with an increase in the inclination angle, exhibits a mild peak, and then decreases. The wake formed behind the bubble and the shearing and buoyancy forces acting on the bubble are mainly responsible for this phenomenon. In the wetted pipe the rising velocity of a single bubble agrees with the equation proposed by Bendiksen et al. An empirical equation is proposed for the rising velocity of a bubble in the poorly wetted pipe.