Relation of turbulent mass transfer to a wall at high Schmidt numbers to the velocity field

Abstract

Turbulent mass transfer to a wall at high Schmidt numbers is controlled by the velocity field within the viscous sublayer. Measurements have been obtained of the root-mean-square fluctuating mass transfer coefficient and the frequency spectrum of the fluctuating mass transfer coefficient for a Schmidt number of about 2300. From an order-of-magnitude analysis it is concluded that flow fluctuations in the direction of mean flow have little effect on the mass transfer fluctuations. A comparison of the mass transfer spectrum with the spectrum of the component of the velocity gradient in the transverse directionszreveals that the high-frequency portion of theszspectrum is not effective in transferring mass. Approximate relations between the mass transfer spectrum and theszspectrum are developed for high frequencies and for low frequencies.