(586f) Transport and Clogging of Fibers in Millifluidic Channels

The transport of particles in strongly confined geometries is a complex process, especially when the particle size becomes comparable to the channel size. Deposition and assembly of suspended particles due to an interplay of hydrodynamics, steric and colloidal forces can lead to clogged channels. Clogs dramatically alter the operating conditions of several natural and engineering systems, and is central to the disruption of flow in a wide range of applications including 3D printing, additive manufacturing, and formulated product synthesis. Even for seemingly simple particles, the mechanisms underlying clogging involve a delicate interplay of geometry, fluid-structure interactions and contact with the boundaries. Clogging dynamics become even more complex for rod-like particles, where particle anisotropy, flow-induced reorientation, and nontrivial frictional dynamics with the walls become relevant. In this work, we explore the transport and clogging of fibers in millifluidic channels using a combination of experiments, theory and computations.

Using tunable 3D printed millifluidic devices, we examine the transport of non-Brownian neutrally buoyant nylon fibers dispersed in a Newtonian fluid. We first quantify the clogging probability of a fiber when flowed through a constant-cross-section bend as a function of fiber length, channel width, bend angle and wall curvature. We discover that fibers do not clog the bent channel if they do not touch at least two points in the channel walls, which we translate to a geometric condition for clogging. Using numerical simulations of these systems based on resistive-force theory coupled to a friction model for wall contact, we then map out a phase space of initial particle configurations and lengths that demarcate cases where the fiber is clogged, finding qualitative agreement with experiments. We then perform exploratory numerical studies of transport and clogging through constrictions, correlating clogging probability to fiber realignment as it approaches the constriction. We illustrate the role of fiber length relative to constriction and the curvature of the boundaries in inducing a clog. Together, these insights build toward a mechanistic understanding of clogging and transport of anisotropic particles in porous media, and in developing guidelines on the design of clog-resilient fluid systems that involve suspensions of fibers.