Hydrodynamic boundary layer at a rising air bubble and entrapment of fine solids: Gravity effects on particle–bubble interactions

ABSTRACT

A model study of the dynamic interactions of fine non-neutrally buoyant solids with background boundary layer (BL) flow on rising bubbles is developed. The aim is to clarify the specific role of the gravity effects. The approach is based on the acquisition of asymptotic equations about the disturbed flow field in the particle vicinity and accounts for both viscous deformation and sedimentation effects. It is established that two particle density regions are of major interest. In Region I the coupling of hydrodynamic and gravity effects results in granulometric separation of the solids. In Region II the role of particle sedimentation dominates over the purely hydrodynamic interactions. As a result, the lighter the particles are, and the smaller their sizes are, the more important is the granulometric effect inside the BL. For high-density fines and larger bubbles, the gravity effects couple with the BL flow. The particle capture results in significant amplification of the collision chances. The obtained results are expected to refine the approach to recovery of fine species from ground materials in conventional flotation and should be taken into account in the assessment of the overall capture efficiency for fine particles in microflotation and separation processes.

GRAPHICAL ABSTRACT

KEYWORDS:

• Fine solids
• granulometric separation
• gravity effect
• hydrodynamic boundary layer
• particle/bubble interaction

Acknowledgments

I wish to express my special thanks to Prof. Elena Mileva, DSc, for the fruitful discussions of the present results and for the long-standing collaborative work together.