DRAG COEFFICIENTS FOR AIR BUBBLES RISING ALONG AN INCLINED SURFACE

An experimental study was conducted to measure rise velocities of air bubbles along an inclined flat wall for small Weber numbers. In the case of a freely rising air bubble, good agreement was obtained with the theoretical drag coefficient values of Ryskin and Leal. For a given working fluid, the rise velocity decreased monotonically as the confining wall was inclined from the vertical. For the case of a nearly vertical confining wall, the rise velocities were in good agreement with Hestroni et al.'s analysis as long as the air bubbles were nearly spherical. The drag coefficients of the bubbles were found to be uniquely correlated with the bubble Reynolds number and the Eotvos number, modified to account for the angle of inclination of the confining wall. The Reynolds number varied from 0.3 to 130 with the Weber number varying from 0.008 to 1.6.