ABSTRACT
Boiling is a phase change process in which vapor bubbles are formed either on a heated surface and/or in a superheated liquid layer adjacent to the heated surface. It differs from evaporation at predetermined vapor/gas-liquid interfaces, as it also involves creating these interfaces at discrete sites on the heated surface. A boiling curve similar to that in pool boiling is obtained when flow occurs over the heater surface (external boiling) or inside a heated tube (internal boiling). In internal flow boiling, the vapor/liquid flow configurations change due to the addition of vapor along the flow direction. Fully developed nucleate boiling curves (B’C’) at different velocities generally overlap each other, suggesting the dominance of the heat removal by phase change. In fully developed nucleate boiling, bubble merger occurs at the heated surface. However, the phasic structure is influenced by the flow regime that exists in the bulk.
