Comparison of rheological properties of fiber suspensions with model predictions

The rheological behavior of fiber suspensions in a Newtonian fluid is compared with the simulations results of two families of models. The well-known Folgar-Tucker model for fiber motion, combined with the Lipscomb constitutive equation, was used and compared to an extended Jeffery model developed by Grmela et al. (2004). The high shear-thinning behavior and the constant normal stress differences predicted by this model, for the fiber suspensions in Newtonian matrix, required modifications and the stress tensor equation was replaced by the Lipscomb constitutive equation. The steadystate and stress growth behavior of fibers suspensions in a Newtonian polybutene are fairly well predicted by both models. The viscosity and normal stress overshoots during stress growth in forward and reverse flows are better described by both models when using a slip parameter and l larger than 1 in the Folgar-Tucker-Lipscomb model. The extended Jeffery model has more potential to describe properly the behavior of concentrated fiber suspensions, but this is achieved by using a large number of parameters.