Breakup and coalescence models for turbulent air-water mixtures in a vertical pipe

The evolution of bubble size distribution and radial air volume fraction was studied by an efficient 1D test solver. New constitutive models for bubble coalescence and breakup due to different mechanisms, including coalescence due to turbulent fluctuation, velocity shear and wake entrainment, and breakup due to turbulent fluctuation, velocity shear and interfacial slip velocity, was proposed. Simulation results showed that at relatively low superficial gas velocities, the bubble size was small and had a narrow distribution, and coalescence was predominant; with an increase in the superficial gas velocity, large bubbles began to form due to the dominance of coalescence, resulting in a much wider bubble size distribution, and breakup became dominant. The simulation results were compared with the recent experimental data achieved on the TOPFLOW facility and good agreements were achieved.