Influence of bubble surface loading on particle-laden bubble rising dynamics in a fluid flow system

Prediction of the rising behaviour of particle-laden bubbles in turbulent flow systems is fundamental to the design and operation of industrial separation processes. However, due to the complexities of such systems, the effect of fluid flow on the rising behaviour of particle-laden bubbles is often ignored. This study examines the combined effect of bubble surface loading (BSL) (particle diameter: 115 mu m and 316 mu m) and fluid flow on the rising behaviour of a particle-laden bubble (bubble diameter: 2.10 +/- 0.08 mm) in a flow system with a pair of counter-rotating vortices, at Reynolds numbers (Re) ranging from 188 to 769. Specifically. the rising trajectory, rise velocity, and aspect ratio of the particle-laden bubbles were determined using the shadowgraphy imaging technique. The results showed that the rise velocity reduces as the BSL increases, reaching a plateau at BSL values > 50%. Over the range of tested conditions, the critical BSL value was appeared to be insensitive to particle size but increased as Re increased. The diminishing bubble surface mobility is believed to be responsible for the observed trend. Further, a drag modification factor as a function of BSL and Reynolds number has been devel-oped. Noticeably, the drag coefficient curves peaked at the corresponding critical BSL values. The drag modi-fication factor may prove to be useful in modelling of the particle separation processes.