Interfacial mass and heat transfer during evaporation: II. Effect of monomolecular films on natural convection in water



The reduction in evaporation from a water substrate and the accompanying change in heat transport through the water induced by monolayers of cetyl alcohol and stearic acid are investigated. Evaporation resistance of the monolayer and Nusselt number in the water are determined at 2° to 22°C. The evaporation resistance increases with increasing surface pressure of the monolayer. In the presence of natural convection in the water, the Nusselt number decreases during monolayer compression. This reduction is larger than could be expected just from the lowered evaporative heat flux and the resulting reduction in the Rayleigh number. It may be due to a change in the surface hydrodynamic characteristics caused by the monolayer.