Mechanisms of heat and mass transport at gas-liquid interfaces

Abstract

Interfacial transport in turbulent liquid flows has been studied in a flume. Flow visualization experiments indicate that turbulence structure near boundaries (interface or wall) is governed by the shear rate. For low values of the interfacial shear rate, ‘patches’ are observed at the interfaces that are formed from the ejections generated near the wall. The ejections are seen to reach the interface, form renewed surface patches, return and mix into the bulk flow. For high values of the inlerfacial shear rate, the low-speed/high-speed streaks are formed at the interface that break down as ‘bursts’. The qualitative features of the streaks and bursts are similar to the ones observed near the wall, even though the boundary conditions are different. From these observations, it appears that the scalar transport at the interface is dominated by different mechanisms depending on the interfacial shear rate. For low shear rates that lead to patches, transport rates are related to parameters associated with these patches (patch area and patch residence time). For shear rates high enough to form streaks and bursts in the interface region, transport rates are obtained considering that the interfacial bursts/ejections govern the process. Both models show excellent predictions of the transport coefficients near the non-wavy gas-liquid interfaces.