Behavior of air bubbles in aqueous wood pulp suspensions

The migration of air bubbles in flowing and quiescent wood pulp suspensions were investigated by flow visualization. The bubbles migrated upwards in a series of random steps as they became repeatedly mechanically-trapped and then escaped from pulp flocs. Mechanical entrapment in flocs occurs when the bubble diameter is greater than the dimensions of the inter-fiber void spaces, and the buoyancy pressure of the bubble is less than the yield stress of the floc.