Possible Mechanism for Formation of Nonwettable "Dry Spots" on a Heated Surface during Nucleate Pool Boiling: II. Feedwater Stop Regime

The problems of simulation of heterogeneous nucleate pool boiling on a horizontal surface on the ascending branch of the boiling curve from the formation of a steam lens (SL) to the boiling crisis are considered. The proposed hypothesis provides in a number of cases a logically consistent interpretation of experiments and outlines the organizational principle of transferring the wall-liquid-steam system into the regime of nonwettable "dry spot" formation. The model includes the following types of nucleate boiling: (a) cyclic boiling with the contact line reverse to the bubble bottom center and bubble departure from the surface (at low heat flux q and the contact angle theta < 90A degrees); (b) single steam bubble conversion into a steam lens, i.e., local film boiling with the possibility of spreading of a single "dry spot" at the variation of the contact angle theta >= 90A degrees, and substantial growth of the departure diameter D (d) and SL lifetime tau d; (c) formation of a single steam cluster of four SLs at a given pressure, the liquid underheating, and the average wall overheating.