Eddy Diffusivity in the Viscous Sublayer

Resumo

An attempt is made to resolve a long standing difference in the predicted distribution of the eddy diffusivity in the viscous sublayer, where the literature shows a dependence on either the cube or the fourth power of the distance from a solid wall. The resolution suggested is that a y³ dependence prevails very close to the wall while a y⁴ dependence may prevail in the outer part of the viscous sublayer near the border with the outer turbulent flow. However, at high values of the Schmidt number, the overall mass-transfer rate will show behavior corresponding to the y³ dependence, and any hints of the y⁴ dependence would be very hard to observe experimentally.