Bubble sweeping heat transfer mechanism for low flux boiling on downward-facing inclined surfaces

The theoretical analysis of nucleate boiling heat transfer from an inclined heated surface facing downward is presented. Mathematical models for latent heat transfer by rising bubbles and sensible heat transfer by removal of the superheated layer are developed under low-heat-flux conditions to explain why the boiling curves for inclined surfaces facing downward shift with the surface orientation angle. It is shown that the bubble departure diameter and wall heat flux at a fixed superheat can be influenced by the surface orientation and by contact angle hysteresis when the heat flux is low. At low heat fluxes, nucleate boiling heat transfer is associated with bubbles sliding along the surface, stripping downstream superheated liquid off the surface.