Capture of hydrophobic particles by freely rising buoyant bubbles

Buoyant bubbles rising through a suspension of particles can remove hydrophobic particles and carry them upward, leaving hydrophilic particles in the slurry. Here, the passage of a layer of buoyant bubbles through a suspension of hydrophobic particles is examined using fully resolved numerical simulations. Particles colliding with the bubbles are attached, using a simple attachment model. The particles move into the bubble until the contact angle of the triple line is equal to the static angle and slide toward the back of the bubbles, where they accumulate and reduce the rise velocity of the bubbles due to their weight. The passage of the bubbles reduces the volume fraction of the freely suspended particles, as the captured particles are carried upward with the bubbles. A simple averaged drift flux model is introduced to model the rise of the bubbles and their scavenging of hydrophobic particles, and it is shown that relatively simple closure models capture the evolution reasonably well.