Interaction Between Bubbles and Solids: Three Applications

The main objective of this study is to understand the interactions of solid particles with bubbles in three different situations: interaction between a bubble and solid particles attached at its interface in the liquid layer of a waste tank at the Hanford nuclear reservation; interaction between flowing foam (agglomeration of bubbles) and fine solid particles in porous media; and behavior of bubbles in an unconsolidated porous medium formed by particulates in the sludge layer of Hanford waste tank. A bubble in the midst of a liquid layer can be coated by small solid particles suspended in the liquid phase, giving the bubble an "armor". Numerical simulation shows that this armor can stabilize bubbles against diffusion by reducing the curvature of the gas-liquid interface. Stress between the solid particles caused by the change in interface shape can be very large. But a Vl thermodynamic free-energy calculation shows that a bubble would still not expel solids from the interface to relieve this stress. Coreflood experiments suggest that foam can transport significant amounts of fine particles far enough within a porous medium to cause large reduction in permeability. The amount of fines transported depends on particle properties such as wettability and surface adhesion. Foam appears to have been stabilized in these experiments by PMMA (polymethylmethacrylate) and montmorillonite, but destabilized by kaolinite particles. Bubbles trapped within the sludge of a Hanford waste tank expand and contract in response to ambient pressure changes. Numerical calculations based on a one-dimensional pore-network model show that the effective compressibility of bubbles shows hysteresis with pressure increase and decrease. This hysteresis is caused by the unsteady, impulsive movements of interfaces, which are from pore throat to throat during a pressure decrease and from pore body to body during a pressure increase. Fitting of numerical results to actual waste level changes in the tank implies that bubbles are long and the ratio of pore-body radius to pore-throat radius is close to one in the sludge layer; however, capillary effects can not be quantified unambiguously.