The effects of surface films in damping eddies at a free surface of a turbulent liquid

Abstract

Mass-transfer rates across a gas liquid surface into a turbulent liquid depend markedly on the hydrodynamic behaviour of the liquid immediately subjacent to the interface. Though turbulence is always somewhat damped at a free liquid surface, there may remain significant movements of liquid into the plane of a clean surface. A very small amount of surface-active material, however, sets up gradients of surface tension between different parts of the surface, and the accompanying (elastic) stresses are shown to damp very strongly eddies approaching the surface, thus reducing the rate of ‘surface renewal’: mass-transfer of a solute across the liquid surface is correspondingly retarded. This paper treats these phenomena quantitatively, and includes five predictions of the effects of surface-active agents. Comparison is made with published experimental data.