Alignment of carbon fiber and PDMS mixture flowing in 90° elbow channel

Abstract

In this study, flow visualization experiments and computational fluid dynamics simulations are conducted to analyze the rotation of carbon fibers flowing in a 90° elbow channel. In the corner of the 90° elbow channel, a directional change in velocities and velocity gradients results in the rotation of the fibers from a horizontal to vertical alignment. To analyze the fiber rotation, a mixture comprising uncured polydimethylsiloxane and ball-milled carbon fibers is utilized as the working fluid in a flow visualization experiment. The velocity and velocity gradients inside the channel are calculated via computational fluid dynamics simulation and then compared with the angular changes in the fiber rotation along different trajectories inside the elbow corner. A Lagrangian approach using a local coordinate system to trail each fiber along the trajectory is utilized to compare the effects of shear rate on fiber rotation. It is discovered that the fibers are affected by a relatively high local shear rate, and that they propagate with the flow, indicating a parallel alignment in the flow direction while exhibiting a 90° turn at the elbow corner.