Courtesy: Anthony D. Cato and Dan D. Edie, Clemson University

Carbon fibers are manufactured through heating and stretching processes. Poly-Acrylo-Nitrile (PAN) and pitch are the two most common raw products used to produce carbon fibers. Unlike the synthetic PAN based fibers, pitch is a coal-tar petroleum product that is melted, spun, and stretched into fibers. CFD can very effectively model the melting in the extruders and spinning through the spinneret.

POLYFLOW is capable of predicting the temperature rise due to viscous heating during high shear flow of mesophase pitch through the spinneret capillary. Typically, these spinnerets have an exit diameter of 150 mm and the wall shear stresses are in the range 2500 1/s to 7500 1/s. This study focuses on identifying flaws in spinneret design in terms of recirculation in the tapered spinneret capillary, while spinning the high temperature viscoelastic melt. Such recirculating flow can cause degradation of the mesophase pitch and disrupt the structure of the spun fiber. Using Fluent's POLYFLOW software, the spinneret design can be modified to have smoother outflow through the capillary.

Stream function distribution for shear rate of 7500 /s showing recirculation