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Different
regimes of flow in the microfluidic rectifier
Streak lines of flow in the microfluidic rectifier in different regimes. The upper photos show the flow from left to right and the lower photos represent the flow from right to left. The flow of an elastic polymer solution was visualized with fluorescent beads and epifluorescent microscopy. The applied pressures per segment appear in the insets. The photos on the left correspond to linear regime, and low applied pressure, low flux and low Weissenberg number, Wi. The resistance in this regime is the same in the both directions, and the flow lines are smooth and similar. At higher applied pressures and higher Wi, non-linear elastic effects make the flows to look differently, and to exhibit different resistance. The Reynolds number was always below unity. The flow resistance is lower in the direction from left to right, in the upper row. The flow from right to left at large Wi does not lead to stationary patterns and keeps changing chaotically. So, flux through the channel for the flow shown at the top right was almost twice larger than for the flow on the photo at the bottom. Curiously, these streak line images somewhat resemble those in the flow of pure water in the same channel at moderate Re, but in the opposite directions. |