Recirculation and transport processes in segmented laminar flows

Enhancing heat and/or mass transfer rates under laminar flow conditions is critical to a wide variety of problems, such as biological microsensor applications and cleaning of surfaces. In this work, momentum and mass (or energy) transfer aspects of recirculatory flow in segmented liquids under oscillatory flow conditions are investigated both theoretically and experimentally.;Theoretical studies are conducted with the aid of the finite-element numerical method on three different systems: symmetric and non-symmetric transport processes in a liquid in a parallel-plate channel confined by two gas-liquid interfaces, and symmetric mass transfer in a liquid in a parallel-plate channel in the neighborhood of the moving contact line. The analyses always examine the outer region of flow in the limit of small Capillary and Bond numbers. In the first two studies, interfaces are modeled as non-deformable slip surfaces to avoid the complications due to deformability. In the third study, the gas-liquid interface is modeled with all its complications. In all systems, Navier's slip condition is applied in the immediate neighborhood of the contact lines to eliminate the stress singularity that would otherwise arise.;In the experiments, electrochemical principles are applied in the determination of transport rates to the boundary. More specifically, the cathodic reduction of ferricyanide to ferrocyanide in excess supporting electrolyte is utilized in the measurement of current densities using the limiting-current technique.;The effects of geometry-related and flow-related parameters are investigated. Results show that transfer rates at modest oscillation frequencies can be four times higher when compared to those obtained for unsteady-state transport in a stagnant fluid. Results also show that the mobility of the fluid-fluid interfaces has a modest effect on the rate of mass (or heat) transfer, the transfer rate being greatest with zero-stress, free-slip interfaces. On the other hand, the value of the contact angle between the interfaces and the parallel walls has an insignificant effect on the transfer rate in a liquid confined by two gas-liquid interfaces.