Computer Simulations of Elastic Capsule Suspension Flow within Rectangular Microfluidic Channels

Three-dimensional simulations were performed to study the pressure-driven flow dynamics of elastic capsule suspensions within rectangular cross-section channels. The simulations utilize the Lattice-Boltzmann method to model the fluid, as well as an Immersed Boundary method to integrate the elastic forces resulting from the capsule membrane deformation. The capsule volume fraction is held at 10% (i.e., a semi-dilute suspension), while several parameters are systematically varied including the channel Reynolds number (Re), the capillary number (Ca, defining the elasticity of the capsule membranes), and the cross-sectional channel dimensions. Depending on the channel dimensions, each simulation contains between several dozen to several hundred capsules. Flow-induced capsule deformation results from both capsule-fluid interactions (in particular the local shear rate) as well as capsule-capsule interactions. For relatively soft capsules, inertial focusing is observed for Re > 100 characterized by a narrowing of the capsule distribution towards the channel centerline as well as an increase in the cell-free layer adjacent to the channel walls. The degree of inertial focusing is also found to depend on the channel dimensions relative to the capsule diameter. The relative viscosity of the suspension (relative to the capsule-free fluid) and the principal tension within capsule membranes is analyzed within the parameter space described above.