An experimental investigation of the motion of single bubbles under a slightly inclined surface

The movement of single air bubbles under a downward facing inclined solid surface has been investigated in motionless distilled water body. The effects of surface inclination θ and bubble volume V on the terminal Froude number are studied in details. The bubble volume was varied in the 0.3–9 cm3 range and the inclination angles up to 10° in a gravity driven system. For a typical correlation curve of the terminal velocity uT versus the volume at a given inclination it was found that the increase of uT with V is not monotonous and that four distinct sub-regimes, each characterized by a specific bubble shape, exist. The effect of inclination on uT is more sensitive at both low V and low θ. The different sub-regimes are explained qualitatively. In addition, the drag coefficients for moving bubble underneath a solid surface are presented.