Orientation distribution in a dilute suspension of fibers subject to simple shear flow

Abstract

The orientation distribution in a dilute suspension of Brownian fibers subject to simple shear flow is investigated theoretically. The fiber has a large aspect ratio r and may carry charge. The flow strength is characterized by the rotary Peclet number Pe= γ/D, where γ is the shear rate and D is the rotary diffusivity of the fiber. Emphasis is placed on the microstructure of the suspension in strong flows, in which the advection and diffusion are of equal importance in a small region of angular space near the flow direction. A new computational method based on a finite difference scheme is developed to calculate the orientation distribution function and then evaluate the orientation moments. For the case of uncharged rods and 1≪Pe1/3≪r, the obtained orientation moments compare favorably with those deduced from the spherical harmonic method. The effects of the fiber aspect ratio and charge are also investigated when they become crucial. It is found that at a given large Pe, the orientation distribution of uncharged fibers with r∼O(Pe1/3) becomes broad and its peak shifts down towards the flow axis, compared with the case of thin rods with r≪Pe1/3. The microstructure of a suspension of charged fibers depends on the charge distribution and the double layer thickness relative to the fiber length. © 1999 American Institute of Physics.