Homogeneous Nucleation of Vapor at Preferred Sites During Rapid Transient Heating of Liquid in Micropassages

Abstract

Rapid heating of a liquid at the wall of a micropassage may produce homogeneous nucleation of vapor in the liquid in contact with the surface. In such circumstances, nucleation is generally expected to be most likely to occur in the hottest liquid closest to the surface. It is known, however, that in many cases, the liquid molecules closest to the surface will experience long-range attractive forces to molecules in the solid, with the result that the equation of state for the liquid near the surface will differ from that for the bulk liquid. In micro- and nanopassages, this wall-affected region may be a significant fraction of the passage interior volume. Recent investigations of wall force effects on the liquid indicate that these forces increase the spinodal temperature in the near-surface region. The results of these previous investigations suggest that for heated surfaces with nanoscale roughness, protrusion of bulk fluid into crevices in the surface may make them preferred sites for homogeneous nucleation during rapid heating. A detailed model analysis of the heat transfer in a model conical crevice is developed and used to explore the plausibility and apparent mechanisms of preferred-site homogeneous nucleation. The analysis predicts that protrusion of bulk liquid into a conical cavity does, under some conditions, make the cavity a preferred site for the first occurrence of homogeneous nucleation. The analysis is used to examine the range of conditions under which a crevice will be a preferred site. The implications for nucleation near a solid surface during rapid heating are also explored for circumstances similar to those for bubble nucleation adjacent to heaters in microheater reservoirs in inkjet printer heads.