Active Sites in Boiling

Effects of cavity size, shape, and their population on nucleation characteristics of a surface were investigated. A theoretical model has been developed for the stability of a cylindrical cavity in boiling considering the wetting characteristics of the fluid and the transient inertial, viscous, and heat transfer effects. For cavities having small depth/diameter ratio and boiling with organics (low contact angle) the model predicts higher superheats than those predicted by the static equilibrium criterion, and as depth/diameter ratio becomes large, the static criterion successfully predicts the required superheat. The predictions of the model are consistent with the experimental observations made on the natural and artificial cavities made by laser. A qualitative theoretical approach has been presented to predict the population of active sites at different superheats for a given fluid and surface.