"Solutocapillary Marangoni flow induced in waterbody by solute source"

TL;DR

This study combines experimental and analytical methods to investigate solutocapillary Marangoni flows caused by solute sources on water surfaces, revealing flow patterns, cone angles, and effects of solute diffusion on flow strength and duration.

Contribution

It provides the first analytical solution describing solutocapillary flow patterns induced by solute sources and validates it with experimental PIV and PLIF data.

Findings

Flow resembles a doublet flow with inward and outward regions.

Cone angle increases with source strength and Schmidt number, exceeding 80 degrees.

Flow strength and duration are enhanced by reduced solute diffusion coefficient.

Abstract

The aim of this paper is to experimentally and analytically study the solutocapillary flow induced in a waterbody due to the presence of a solute source on its surface and the mixing induced by this flow of the solutes and gases dissolved at and near the surface into the waterbody. According to the analytic solution, the induced flow is analogous to a doublet flow in the sense that the flow is directed towards the source within a conical region with its vertex at the source, and outside the conical region the flow moves away from the source. The half cone angle for a negative source increases from $\sim$60 degrees with increasing source strength and Schmidt number reaching values greater than 80 degrees. When the cone angle is large, the outflow is restricted to a thin annular boundary layer region. These analytic results are in agreement with our experimental data obtained by the PIV (Particle Image Velocimetry) and PLIF (planar laser-induced fluorescence) techniques. As the solute gradient at the surface gives rise to the force that drives the flow, when the solute diffusion coefficient is reduced the flow becomes stronger and persists longer because the solute gradient is maintained for a longer time and distance. In experiments, the flow changes direction into the waterbody and the surface flow stops when the solute induced surface tension gradient driving the flow becomes comparable to the surface tension gradients that exist on the surface due to temperature gradients.