The relative effects of the size of gas sparger orifices and properties of solid particles on gas-liquid mass transfer are not yet fully understood. Here, the impact of sparger orifice sizes, solid particle shapes, and their loading amounts in a bubble column reactor on the absorption of oxygen in tap water was investigated. Their influence on the mass transfer coefficient and bubble hydrodynamic parameters was evaluated. The results show that the addition of solid particles can have both positive and negative effects on hydrodynamics and mass transfer, depending on the orifice size of the gas sparger. The introduction of ring-shaped solid particles can improve the mass transfer rate by up to 28 % without requiring any significant additional power.

This paper presents a demonstration of the visualization and the characterization of gas−liquid mass transfer in a small bubbly column. The aim is to show how simple experiments can be used to directly quantify mass transfer without the need of sophisticated probes or complex titrations. The method here proposed is based on the "red bottle" reaction, i.e., the reversible oxidation by oxygen of dihydroresorufin to red resorufin. This reaction produces a distinctive red color, and in the specific condition identified, the time required to turn from colorless to red solution can be directly correlated with the inverse of the volumetric mass transfer coefficient k L a (s −1). Therefore, this reaction can be used to estimate the mass flux of oxygen transferred from the gas phase (bubbles) to the liquid phase and to study how this flux is affected by geometrical and operating parameters of bubbly flows. The lab work described is thus very convenient for education purposes. This is the first visual demonstration allowing mass transfer to be quantified with good precision, opening up a wide range of applications.