Microlayer evaporation during steam bubble growth

This paper presents analysis of the evaporation of the microlayer beneath a steam bubble growing at a heated surface. The microlayer depletion rate, and the associated evaporative heat flux, have been assessed using optical measurements of its thickness, and infrared measurements of the temperature of the solid surface beneath the bubble. Depletion of the liquid film is modelled from a molecular point of view, and comparison with measurements is attempted. A model of evaporation based on a simple kinetic theory representation of the molecular fluxes impinging on and emitted from a liquid surface is studied. From this, strong support is obtained for the hypothesis that only a fraction of impinging vapour molecules are absorbed by a liquid surface. The measurements suggest a value for the ‘accommodation coefficient’, of approximately 0.03 and a corresponding ‘effective evaporative heat transfer coefficient’, that are reasonably consistent with estimates from other workers.