Computational fluid dynamics simulation of bubble size and local gas holdup in stirred vessel

The bubble size and local gas holdup in a stirred vessel with dual impellers were simulated numerically with computational fluid dynamics, in which the Euler-Euler multiphase flow model, multi-reference frame method and a transport equation for bubble number density (BND) function were combined. The effects of bubble coalescence and breakage were involved in the bubble number density function. The numerical results were in good agreement with the experimental values measured with double-tip conductivity probes. The results show that the bubble size and local gas holdup distribution in the stirred vessel are very non-uniform under relatively high superficial gas velocity. The bubble sizes in the impeller discharge region is quite small and increases with the discharge currents of the impeller. Bubbles coalescences play a dominant role in the inter-impeller region and the region above upper impeller. Local gas hold up is much high just behind the baffles and the blades where cavitation forms and in the centre of circulation loop.