The structure of bubble non-equilibrium movement in free-rise and agitated-rise conditions Original Research Article

Experimental data on the air bubble rise speed νz, the bubble mean lateral displacement sx and the mean frequency fz of bubble periodic movement are presented as funtions of bubble size for pure and contaminated water, in free-rise and agitated-rise conditions. The entire scope of bubble non-rectilinear movement is considered. The interdependence of the νz, sz and fz values, as functions of bubble equivalent sphere diameter de, is is shown to be very consistent. There are two peaks in s, vs. de, the first characteristic for periodic bubble movement and the second for bubble random rocking. In contrast with the work in the literature, where attempts were made to evaluate the drag on the bubble in a way which is consistent only for the firstpeak of sz, the philosophy presented originates from the second peak of sz. Postulating that a visible bubble path is a unit reflection of several microscales which dissipate bubble rectilinear motion, a new definition of bubble drag coefficient as a function of fractal-like dimension is proposed.