Influence of the bubble size distribution on the bubble column flow regime

The role of the bubble size dependent lateral lift force on the flow regime is experimentally investigated in a tall bubble column. In the experiments, only the initial bubble size distribution was modified by using a gas sparger with different injection needles and varying the flow through specific injection needles. The gas flow rate was kept unchanged in all experiments. Depending on the bubble size distribution homogeneous, transitional or heterogeneous flow regimes were observed. The flow regime is in good agreement with the predictions from the stability criterion obtained by a previously done linear stability analysis for poly-dispersed flow. It was found that as a rule of thumb the following criterion can be used.
If most of the gas volume is transported by bubbles smaller than the critical diameter at which the lift force changes its sign, the flow is stabilized leading to a homogeneous flow regime. If most of the gas volume is transported by bubbles larger than that diameter the flow is de-stabilized leading a heterogeneous flow regime. If the fraction of gas transported by small and large bubbles is about the same, the initial conditions remain dominant throughout the column height.