A Numerical Model of the Flow Past a Spherical-Cap Bubble Rising in a Fluidized Bed

The shape and motion of gas bubbles in a fluidized bed are investigated by considering a single spherical-cap bubble rising vertically with free slip at its surface in an incompressible Newtonian fluid. The bubble shape, its terminal rise velocity, and the flow pattern around the bubble have been computed numerically by use of a finite element package solving the Navier−Stokes flow equations. Comparison with experimental findings shows that the bubble shape and the wake fraction can be predicted satisfactorily for a range of bubble sizes by assuming that the fluidized bed behaves as a Newtonian fluid. However, a clear-cut discrepancy was found in the terminal rise velocity. The results indicate that this discrepancy cannot be fully explained from the a priori assumption of the spherical-cap bubble shape, but that, most probably, some non-Newtonian fluid behavior must be invoked.