Modelling bubbly flow and its transitions in vertical annuli using population balance technique

Bubbly flow and its transitions in vertical annuli is studied using population balance technique. Bubble breakup and coalescence is accounted separately to track the evolution of the bubble size during the simultaneous flow of gas and liquid. The conventional two-fluid model is used to simulate the hydrodynamics. The model enables the prediction of voidage profile at any axial location. Presence of peak in the void distribution at the walls of the annulus, center of the annulus and both at walls and centers is observed depending on the phase superficial velocities. Further, transition from bubbly to slug and bubbly to dispersed bubbly is predicted based on the evolved bubble size. The model prediction gives a good match with the experimental data and existing theory. A shift in the transition boundary is noted due to the variation in inlet bubble size and the dimension of the annulus.