Gas bubble injection from an axisymmetric slot in a tube

Gas bubble formation from an axisymmetric slot in the inner surface of a tube is studied both numerically and experimentally. This process has some resemblance to gas bubble injection from multiple orifices at a fixed axial location in a tube, which is encountered in many practical applications. The axial symmetry that is assumed in this problem facilitates the potential-flow boundary-integral modeling which is similar to that of other gas bubble formation cases. As the bubble grows from the axisymmetric slot it takes a toroidal shape. Depending on the liquid flow rate in the tube, one may expect to see the hole in the toroidal bubble getting smaller and eventually blocking the liquid flow. Simulations show that the blockage occurs when the liquid flow rate is small enough. At high liquid flow rates, a toroidal bubble detaches at the slot when the gas flow rate is moderately high. A set of experiments involving air injection in water has also been carried out. At low liquid flow rates, there is agreement between simulations and experiment. Once the bubble blocks the liquid flow by occupying the whole cross section of the tube, it grows as a single bubble and detaches. However, the predicted toroidal bubble detachment at high liquid flow rates is unlikely in practice due to a premature loss of axial symmetry.