Shapes and rising velocities of single bubbles in vertical pipes

Abstract

Shapes and rising velocities of single bubbles rising through vertical pipes were measured under stagnant, laminar flow and turbulent flow conditions to examine the wall effects on the drag force and bubble shape. Experiments were conducted using air and water, and three pipes of inside diameter D = 13.3, 15.9 and 24.8 mm. The ratio λ of equivalent bubble diameter d to D was varied from 0.2 to 2.0 in each experiment. The drag coefficient was correlated in the form of CD0φ(λ) where CD0 is the drag coefficient of a bubble in an infinite stagnant liquid and the multiplier φ(λ) is given as the arithmetic mean of Clift's and Wallis's multipliers. Bubble shapes were expressed as a function of the liquid Reynolds number. It was also confirmed through interface tracking simulation that the proposed correlations are applicable not only to the air-water system but also to a low viscosity system, the Morton number of which is less than 10-8.