Shape of a Vapor Stem During Nucleate Boiling of Saturated Liquids

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Abstract
The transport processes occurring in an evaporating two-dimensional vapor stem formed during saturated nucleate boiling on a heated surface are modeled and analyzed numerically. From the heater surface heat is conducted into the liquid macro/microthermal layer surrounding the vapor stems and is utilized in evaporation at the stationary liquid–vapor interface. A balance between forces due to curvature of the interface, disjoining pressure, hydrostatic head, and liquid drag determines the shape of the interface. The kinetic theory and the extended Clausius–Clapeyron equation are used to calculate the evaporative heat flux across the liquid–vapor interface. The vapor stem shape calculated by solving a fourth-order nonlinear ordinary differential equation resembles a cup with a flat bottom. For a given wall superheat, several metastable states of the vapor stem between a minimum and maximum diameter are found to be possible. The effect of wall superheat on the shape of the vapor stem is parametrically analyzed and compared with limited data reported in the literature.