Theory and Indirect Measurements of the Drag Force Acting On a Rising Ellipsoidal Bubble

Abstract

A series of experiments were performed to obtain the drag force and rise characteristics of oblate ellipsoidal bubbles (OEB) in tap water at room temperature. The experiment utilized a 1.219m tall Plexiglas column with square cross section of 15.24cm sides designed and constructed for this purpose. Photographs captured the bubbles as they rose and grew vertically in the water column, and were analysed to determine the bubble radius. The drag force and velocity of rise were determined indirectly. An equation (CD=2.667/Fr) was derived for the drag coefficient of the OEB where Fr is the Froude number. The merit of this work is in the capability of the bubble's semi-major and semi-minor axes measurement being used to determine the drag coefficient and mean rising velocity of bubbles. Results were compared favourably with the current and published theoretical results.