The promotion of dropwise condensation by monolayers of radioactive fatty acids I. Stearic acid on copper surfaces

Abstract

AbstractA study has been made of the promotion of dropwise condensation by monolayers of stearic acid‐I−14 C on copper. The desorption of promoter during condensation was followed by 14C counting and by autoradiography, and the accompanying increase in wettability was characterised by changes in heat transfer. Rough surfaces were not promoted by a Langmuir monolayer. On a smoot surface the life of dropwise condensation was 10–100 min. Sulphiding the surface before depositing the monolayer increased the life ten‐fold. It was shown that complete coverage of the surface by promoter is not necessary for the promotion of dropwise condensation. The desorption of promoter was uneven and some promoter invariably persisted after the surface had become completely wettable. Condensation was always accompanied by the dissolution of copper, and the change from dropwise to filmwise condensation is attributed to the combined effects of corrosion and promoter desorption.