Distributions of fiber orientation and fiber concentration in slit flows of concentrated suspensions were measured. Slit channels were used in the experiments: a channel with an abrupt expansion and a crank geometry with six L-shaped corners. Such channels are usually used in a polymer processing. For visualization of fibers, an index-of-refraction matching method was employed, and tracer fibers having birefringence were suspended to observe between crossed polarizers. When fibers flow through an abrupt expansion, they rapidly orient in the direction perpendicular to the flow direction near the centerline. The fiber orientation, however, returns to the flow direction in the downstream region. In the L-shaped corner, fibers randomly orient because of the decelerating flow. In the downstream region of the L-shaped corner, fiber orientation is not symmetric with respect to the centerline. This seems to result from fiber-fiber interactions in the concentrated suspension. The fiber concentration is uniform over a width of a channel except adjacent to the side wall in the concentrated suspension, while it has a maximum apart from the side wall in the dilute suspension.

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