Author(s): M. Higashino; H. G. Stefan

Linked Author(s): Makato Higashino

Keywords: Mass transfer; Diffusive boundary layer; Sediment/water interface; Sherwoodnumber; Water quality

Abstract: A model to estimate the development of a diffusive boundary layer is formulated. The information can be used to determine where a microprobe is to be deployed or how long a sediment bed is needed to achieve a certain vertical diffusive flux at the sediment/water interface. The dependence of the mass transfer rate at the sediment/water interface on shear velocity, bed length and the Schmidt number has been investigated. A Sherwood number (Sh) as function of both the distance (x) from the point at which the diffusive boundary layer begins to develop and the Schmidt number (Sc), and a mean Sherwood number (Sha ve) over a distance are introduced to investigate how the boundary flux varies as the diffusive boundary layer develops. The Sherwood number is largest around x=0 and decreases as x increases, and finally, approaches a constant value which is for fully developed diffusive boundary layer (Sh∞). The distance to a fully developed diffusive boundary layer (L99) and the required length (L) of a sediment bed, are related to the Schmidt number (Sc), the shear velocity (U*), and the relative errors of Sh and Sha ve against the Sherwood number for fully developed diffusive boundary layer (Sh∞). Both lengths L99 and L decrease as the Schmidt number increases, and finally become independent of the Schmidt number.

DOI:

Year: 2003