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TURBULENT MASS TRANSFER MECHANISM ACROSS A CONTAMINATED AIR-WATER INTERFACE

Yosuke Hasegawa
Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1, Meguro-ku, Tokyo 153-8505, Japan; Center of Smart Interfaces Technical University Darmstadt Petersenstr. 32, 64287 Darmstadt, Germany

Nobuhide Kasagi
Center for Research and Development Strategy, Japan Science and Technology Agency; Department of Mechanical Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Abstract

Numerical simulation of high Schmidt number turbulent mass transfer across clean and contaminated air-water interfaces is carried out. At the clean interface, the local scalar flux is predicted fairly well from the surface divergence by applying the Chan and Scriven's stagnation flow model. With increasing the Marangoni number, however, the scalar flux is less correlated with the surface divergence and the gas transfer rate detereorates drastically and eventually approaches the value on a solid wall. From an analysis of a one-dimensional advection-diffusion equation, it is shown that the scalar field near the interface is characterized by two time scales, i.e., renewal and transient time scales, and the surface divergence contributes to the mass transfer only when the renewal time scale is longer than the transient time. The effective surface divergence is extracted from time-series data and found suitable for prediction of gas exchange at clean and slightly contaminated interfaces. In the case of the highly contaminated interface, in which the effective surface divergence is strongly damped, the mass transfer is essentially the same as that on a solid wall.