Dealing with the hydrodynamics of bubbles

Imagine a large bubble column with bubbles moving up as reactants. While the bubbles travel upwards, they collide or combine with each other. The combination of the two or several bubbles results in a smaller surface area. Mass transfer and reaction output, being dependent on the surface area, is hampered due to that. In this research a wire-mesh was introduced to cut these large bubbles. The developed cutting model outperforms the present geometrical one while taking into account the effects of surface tension, viscosity and bubble dynamics. It could be applied in reactors such as bubble column reactors which hold potential in converting CO2 to useful chemicals.

Before revealing the details about the bubble cutting, a few words on the lift modeling is necessary. Using a trial and error method, it was found that the lift force in a bubble column is dependent on the bubble proximity and the average vorticity(rotation) in the flow. Moving on, the outcomes of bubble cutting was analyzed by applying energy balance of the bubble focusing on buoyancy and surface tension, based on several bubble-wire interacting configurations. Upon analysis, it was observed that a narrow mesh spacing and a smaller bubble Eötvös number generally results in bubbles getting stuck underneath the wire. The derived energy balance is generalized to large meshes with multiple openings and different configurations.

Insights into bubble cutting design

Finally, a model based on the outcomes of energy-balance analysis is proposed for simulating micro-structured bubble columns. This model is tested with different experiments and it is found that the model functions very well, even for cases with moderate to high superficial gas velocities. These models can be used to provide insights into bubble cutting design.

Title of PhD thesis: Numerical modeling of microstructured bubble columns. Supervisors: Prof. Niels Deen, and Dr. Yali Tang.