Analysis of flow-induced structure of polynieric fluid in a miatchannel for processing of nano composite materials

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Flow-induced structure of polymer solutions has been estimated quantitatively around a small circular obstacle in a small channel, which has a 4 mm width and 1 mm depth. We made an original optical system to measure the birefringence of the test liquid, which corresponds to the change of the structure at a high resolution in a space of 0.1 mm step. Furthermore, we measured velocity distributions in the flow channel. As a result, in the upstream of the obstacle, the degree of molecular orientation decreases as the fluid particle flows towards the obstacle because the molecular orientation is aligned in the direction perpendicular to the flow due to the decelerating flow. Just upstream the obstacle, however, the degree of molecular orientation became large because the orientation is almost perfectly aligned in the direction perpendicular to the flow. On the other hand, in the downstream of the obstacle, the degree of molecular orientation became large as the fluid flows in the direction of the downstream due to the elongational flow. These measurements were carried out in a very small region in a channel space.Next, we measured the flow pattern and the velocity distribution in the flow of nano fiber suspension made of bacteria cellulose (BC fluid). The flow was visualized in the channel having rectangular cross section and a 4: 1 contraction. The velocity profile of the Newtonian fluid had a parabolic-like flow, but a plug-like flow in a BC fluid. The larger concentration of the BC became more plug-like velocity profile, because the BC fluid has a shear-thinning viscosity. Furthermore, we measured the vortex enhancement in the reentrant corner at the contraction. As a result, the vortex in the BC fluid became larger than that in a Newtonian fluid. This is because the BC fluid has a large elongational viscosity.