Effect of Superhydrophobic Internals on Flow in a Bubble Column

This study investigates the influence on bubble dynamics of superhydrophobic coatings on internal components within a bubble column. Multiphase flows similar to those considered are relevant to heat exchangers and rod bundles, and we hypothesize that superhydrophobic-coated internal components will result in a change of flow regime, which can be beneficial for maximizing heat transfer performance or avoiding an undesirable operating regime.The presence of a superhydrophobic surface can enable gas to escape faster to the free surface along solid surfaces. This can result in reduced gas volume fractions compared to conditions without superhydrophobic coated internals and allow the flow to remain dispersed at higher gas fluxes. Advanced measurement techniques can measure the phase fraction in these optically opaque systems. We employ multi-plane wire mesh sensors and X-ray computed tomography to study flow patterns in a bubble column with and without internals. We observe for low gas fluxes a minimal effect from the coating, but for a gas flux that in our column leads to a void fraction exceeding 0.2 we observe a plateau in phase fraction as gas layer indeed forms an 'escape route' to the free surface along the superhydrophobic surfaces. The overall flow pattern is significantly modified, and flow remains in a disperse regime in most of the column at higher gas fractions.