Effects of Turbulence and Containing Wall on Rise Velocities of Single Bubbles in a Vertical Circular Pipe

Experiments were conducted to clarify the single bubble rise characteristics in turbulent flows in vertical flow channels. It was revealed that the rise velocity of a bubble relative to the time-averaged local liquid velocity could be much smaller in turbulent upflows than in stagnant liquids. The reduction of relative velocity was estimated to be caused by the two factors: turbulence in continuous phase and steep velocity gradient near wall; new correlations for describing these two effects were proposed. The relative velocity between the phases significantly affects the lateral phase distribution in multidimensional simulation of bubbly two-phase flow and the present correlations can give reasonable predictions for the relative velocity in turbulent flow. It is hence expected that the new correlations can contribute to the further improvement of the simulation models of bubbly two-phase flows.