I. Experimental observations of the microlayer in vapor bubble growth on a heated solid. II. An investigation of the theory of evaporation and condensation

Citation

Koffman, Larry Douglas (1980) I. Experimental observations of the microlayer in vapor bubble growth on a heated solid. II. An investigation of the theory of evaporation and condensation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/M1H1-S690. https://resolver.caltech.edu/CaltechETD:etd-12082006-131228

Abstract

Two fundamental problems related to the evaporation of the microlayer formed beneath growing vapor bubbles on a solid surface are investigated. First, experimental measurements of microlayer formation and evaporation have been obtained for nucleate boiling of water and ethanol using laser interferometry combined with high speed photography. For pool boiling of water at atmospheric pressure with low subcooling, the initial microlayer profile is wedge-like with a thickness of 1.85 µm at a radius of 0.25 mm; the thickness for ethanol is approximately 1.6 times that for water. The measured evaporation rates from the microlayer correspond to local heat fluxes of the order of 1000 kW/m2 over the bubble lifetime. The measurement technique of laser interferometry is discussed in detail with emphasis on the difficulties encountered in interpretation of the fringe patterns. In the second investigation, the theory of evaporation and condensation is considered from a kinetic theory approach. The moment method of Lees is used to solve the problem of the flow of vapor between a hot liquid surface and a cold liquid surface. A result of the theory is that the temperature profile in the vapor for the continuum problem is inverted from what would seem physically reasonable. Because of this behavior, the theory is questioned on physical grounds leading to the conclusion that the usually assumed boundary conditions for emission of molecules from a liquid surface are probably incorrect.

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