(299d) Drift and Diffusion of Rigid and Flexible Fibers in Simple Shear Flow

Economic biomass processing can be challenging because of difficulties associated with mixing and transporting fibrous biomass slurries. The dynamics of fibers in biomass slurries are studied by computer simulation in order to gain insight into the factors that govern their transport behavior. A new phenomenon was found for the motion of isolated, curved, rigid, neutrally-buoyant, non-Brownian, nonchiral fibers in simple shear flow of an incompressible Newtonian fluid at low Reynolds number. For some initial orientations, fibers with small curvature drift steadily in the gradient direction without external forces or torques. The average drift velocity and direction depend on the fiber aspect ratio, curvature and initial orientation. The drift results from the coupling of rotational and translational dynamics, and the combined effects of flipping, scooping, and spinning motions of the fiber. In suspensions of flexible fibers, the shear-induced diffusion caused by collisions between fibers depends on equilibrium shape, fiber aspect ratio, static friction between contacts, and concentration. While collisions between fibers increase the diffusivity, the formation of fiber networks decreases the mobility of individual fibers and decreases the diffusivity.