Assessment of the flow behavior of power-law fluids in spinnerets

We employed the computational fluid dynamics (CFD) simulation to capture the flow behavior in spinnerets based on various flow angles (90 degrees, 75 degrees, 60 degrees, and 30 degrees), different power-law fluids (0.5 < n < 1), and two different flow rates (0.2 mL/min and 1.4 mL/min). The simulation results moderately agreed with the semi-analytical solution obtained from the literature. The sensitivity analysis was performed, showing that spinneret's flow angles and powerlaw indices are additional critical variables that facilitate the alignment of the polymeric chain in the dope solution due to the enhanced shear rate. The maximum viscosity reduction is observed in this study when a more shear-sensitive dope fluid extrudes through the spinneret at a given flow rate. The low shear rate gradient prevalence elevates the viscosity in the annular spinneret region, strongly dependent on the flow and shear-sensitive fluid (n < 1). The trends of dimensionless velocity, shear rate, and viscosity distribution are independent of the dope solution flow rates at the exit of a spinneret except for the more shear-sensitive fluids at 60 degrees flow angle spinneret. We attempted to correlate the shear rate and viscosity distributions of the dope solution at the exit of the spinneret with the literature finding on the hollow fiber morphology under wet spinning conditions. It shows a possibility of producing finger-like macrovoids near the outer/inner membrane layer while extruding the hollow fiber through straight/conical spinneret due to relatively low shear rate and lower viscosity region. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.