Computational analysis of the selective capture of binary mixtures of particles by a bubble in quiescent and fluid flow

Abstract

This paper presents a computer simulation analysis of the selective capture of binary particle mixtures by a central bubble, as influenced by the relative strength of the hydrophobic interaction assigned to each type of particle. The analysis was carried out for a quiescent fluid using two different configurations of initial particle positions, namely: spherical (particles released from within a spherical shell surrounding the bubble) and top (particles released from a horizontal plane located above the bubble) distributions. The top distribution was also used to study the effect of fluid velocity (<0.05m/s). The results show that in the case of a quiescent fluid the collection efficiency was greater for the top distribution than for the spherical one. In addition, when the strength of the hydrophobic force was less than the net particle weight, particles easily detached from the bubble surface. In the presence of fluid flow the collection efficiency followed an exponential decay with the fluid velocity and a quadratic relationship with an effective cross-section for the particle-bubble collision. The latter closely follows the collision models in the literature. Importantly, we have shown that selective capture only occurs when one type of particle possesses a hydrophobic force magnitude close to or less than the net particle weight, while the hydrophobic force for the second type needs to be much larger than the net weight of the particle. Therefore, we have concluded that selectivity does not depend solely on the hydrophobicity differences, but also requires that one type of particle has to be weakly interacting with the bubble.