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 ca se of a freely rising air bubble, good agreement was obtained with the theoretical drag coefficient values of Ryskin and Leal. For a given w orking fluid, the rise velocity decreased monotonically as the confini ng wall was inclined from the vertical. For the case of a nearly verti cal confining wall, the rise velocities were in good agreement with He stroni et al.'s analysis as long as the air bubbles were nearly spheri cal. The drag coefficients of the bubbles were found to be uniquely co rrelated with the bubble Reynolds number and the Eotvos number, modifi ed 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 f rom 0.008 to 1.6.