Wall Interactions

The interaction of drops and bubbles with solid walls affects their motion and the general dynamic behavior. Since the infinite continuous phase is an approximation for a large container, or otherwise distant boundaries, many situations would call for the understanding of the fluid mechanics along with the heat and mass transfer associated with drops and bubbles near boundaries. In particular, the presence of solid boundaries requires serious consideration. Some common examples are the problems associated with dispersed flow in tubes, or interaction of sprays with solid materials. Wall effects in heat transfer are especially important because in many instances the wall is the heat source or the heat sink. The thermal behavior, to a large extent, depends on the fluid flow. There are instances, however, that are weakly dependent on the fluid flow, such as in dropwise condensation. We will first discuss the fluid mechanics concerning the interaction of drops and bubbles with solid walls. Fluid particles near, as well as in contact with, walls are considered in this discussion. The coverage is to the extent of direct application to convective transport of energy or solute. While topics such as cavitation and boiling are discussed briefly, some other areas such as bubble motion in tubes have not been considered. Topics dealing with pure fluid mechanics with inconsequential or undeveloped heat or mass transfer results are not included.