Reynolds number stratified flow

When multi-liquids co-flow in a microchannel, there form interfaces between them due to the low Reynolds number. This is known as liquid-hquid stratified flow. 

Liquid-liquid stratified flow in microchannel is often used in biological analysis, such as during ion exchange or solvent extraction from one phase to another phase [1]. For liquid flow in microfluidics, the Reynolds number is small and the flows are always laminar. Laminar fluid diffusion interfaces (LFDIs) are generated when two or more streams flow in parallel within a single microstructure [2], as shown in Fig. la. 

The data-base which has been found suitable for extracting the information on the dynamic interaction and correlating the dynamic interfacial shear stress component consists of the fluids flow rates along a stratified-smooth/wavy transitional boundary. More experimental data is needed to further substantiate the correlation for the dynamic coefficient. In particular, there is a need for additional data on this transition in systems of high liquid Reynolds numbers (e.g., high pressure steam/ water systems and large diameter tubes) and in two-fluid systems of either comparable phase velocities or faster lower turbulent layers (e.g., viscous-oil/water systems, downward inclined gas liquid systems). 

Recently, an analysis of stratified mixing layers at different Ri and Pr numbers has been performed. With the help of mathematical models for visualising flow structures and temperature fields a direct comparison of simulation results, obtained for various Prandtl and Reynolds numbers, is possible. The drastic effect of Pr on the temperature distribution in a neutral mixing layer is demonstrated in figure 5. 

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