Bubble Cutting by Cylinder – Elimination of Wettability Effects by a Separating Liquid Film

A Model for the Fate of a Gas Bubble Interacting with a Wire Mesh

In the concept of a microstructured bubble column reactor, microstructuring of the catalyst carrier is realized by introducing a static mesh of thin wires coated with catalyst inside the column. Meanwhile, the wires also serve the purpose of cutting the bubbles, which in turn results in high interfacial area and enhanced interface hydrodynamics. However, there are no models that can predict the fate of bubbles (cut/stuck) passing through these wires, thus making the reactor optimization difficult. In this work, based on several typical bubble-wire interacting configurations, we analyze the outcomes by applying the energy balance of the bubble focusing on buoyancy and surface tension. Two limiting cases of viscosity, corresponding to the ability of the bubble to reconfigure into the lowest energy state, are investigated. Upon analysis, it is observed that a narrow mesh spacing and a smaller bubble Eötvös number generally result in bubbles getting stuck underneath the wire. We have obtained the threshold grid spacing and the critical Eötvös number for bubble passage and bubble cutting, which are verified by the direct numerical simulation results of bubble passing through a single mesh opening. The derived energy balance is generalized to large meshes with multiple openings and different configurations. Finally, a closure model based on the outcomes of energy-balance analysis is proposed for Euler-Lagrange simulations of microstructured bubble columns.

Euler-Lagrange Simulations of Microstructured Bubble Columns Using a Novel Cutting Model

In the concept of a microstructured bubble column reactor, meshes coated with catalyst can cut the bubbles, which in turn results in high interfacial area and enhanced interface hydrodynamics. In previous work, we developed a closure model for the fate of bubbles interacting with a wire mesh based on the outcomes of energy balance analysis. In this paper, the model is validated using Euler-Lagrange simulations against two experimental cases of microstructured bubble columns. Before validation of the model, the definition of the deceleration thickness, as used in the calculation of the virtual mass term, is refined to introduce the effects of liquid viscosity and wire thickness. Proceeding with the validation, the inclusion of our cutting closure model results in an excellent match of the bubble size reduction by the wire mesh with the experimental data. Consequently, the simulations produce a more accurate prediction of the reactor performance for the gaseous reaction in view of the pH and gas holdup profiles. The effect of liquid viscosity on the bubble size reduction by the wire mesh is replicated accurately as well. Noticeably, the significance of bubble coalescence and breakup in bubble dynamics overperforms the role of bubble cutting at high superficial gas velocities; thus, further improvement is needed there. Finally, based on the validated cutting model, we share some perspectives on the design of wire meshes to increase the bubble interfacial area.