the regions near the walls were devoid of the particles. Since the particle-rich region divided equally at the bifurcation, the particles were partitioned equally between the daughter branches for θ = 00. For the other cases (θ = 300 and 450) particles prefer the branch which receives high flow rate. As the flow rate in the main branch increases, the particle-rich central core preferentially enters into this branch. On the other hand, the material that enters into the side branch originates from the wall regions of the inlet branch which is devoid of particles. The particle partitioning between the daughter branches does not exactly follow the bulk suspension. These results show that the width of the daughter branches influence the flow and particle partitioning.
4.4 Closure
The main theme of this chapter is to study the effect of shear-induced migration phe- nomenon on the velocity and particle distribution by using DFM and SBM. The particles considered in the present study was non-colloidal, mono-dispersed and neutrally buoyant in the Stokes regime. The ability of particles to form non-uniform configurations influ- ences many aspects of suspension behavior in a bifurcation flow. The features which are greatly affected by the nonuniform distribution of the particles include the detailed con- centration and velocity profiles in each branch, position of the dividing streamline, flow and particle partitioning. Subsequently, we have carried out numerical experiments to explain the aforementioned features in the oblique bifurcating channel. The suspension fluid velocity profiles showed a marked difference over pure carrier fluid velocity profiles and greatly depends on the orientation of the geometry (bifurcation angle). After the bifurcation, the velocity and concentration profiles become asymmetric and degree of asymmetry depends on the bifurcation angle. As the bifurcation angle increases, the di- viding streamline shifts towards the side branch and suspension shows slightly different behavior over pure carrier fluid. The partitioning of the particles does not follow the fluid partitioning. The findings of DFM and SBM were very similar. The results which
4. Suspension flow through a 3D oblique bifurcating channel
we have shown are useful in the microfluidics.
Chapter 5
Effect of carrier fluid rheology on shear-induced particle migration
5.1 Overview
The literature mentioned in chapter1addressed the shear-induced migration phenomenon and fluid-particle partitioning through symmetric and asymmetric bifurcating channels considering the carrier fluid as a Newtonian fluid. Within the Stokes flow regime, as long as the suspending fluid is Newtonian, the magnitude of the suspending fluid viscosity hardly affects the distribution of the particles and fluid-particle partitioning (Abbott et al., 1991). Karnis and Mason (1966) first reported the impact of the nature of sus- pending fluid on the particle trajectories. They have carried out experiments for a single particle in a shear-thinning fluid and observed that the particle moves towards the wall, whereas in the Newtonian fluid the migration is towards the channel center. Later,Gau- thier et al. (1971) and Huang and Joseph (2000) also confirmed the findings of Karnis
Published as:
• M.M. Reddy, P. Tiwari and A. Singh. (2019). Effect of carrier fluid rhe- ology on shear-induced particle migration in asymmetric T-shaped bifurcation channel.
https://doi.org/10.1016/j.ijmultiphaseflow.2018.10.005.
5. Effect of carrier fluid rheology on shear-induced particle migration
and Mason (1966). Rao et al. (2002) through numerical simulations investigated the effect of the shear-thinning nature of the carrier fluid on the shear-induced migration of neutrally buoyant particles. Their results led them to conclude that self-diffusivity coefficients in the original model of Phillips et al. (1992) needs to be corrected for the extension to non-Newtonian carrier fluids and proposed the values for diffusivity coeffi- cients. Later, Lam et al. (2004, 2002) through numerical simulations and experimental studies investigated the particle migration during pressure-driven tube flow of dense sus- pension in the shear-thinning carrier fluid. Effects of different viscosity models of carrier fluid on particle migration during non-homogeneous shear flow were investigated using the model of Phillips et al. (1992). The constant empirical parameters were arrived at by fitting the particle concentration data between experimental observations and nu- merical predictions. In our study, we have employed these values to study the effects of non-Newtonian carrier fluid on particle migration in asymmetric bifurcation chan- nels. Recent studies have indicated that the particle partitioning between the daughter branches of a bifurcating channel strongly depends on the rheology of suspending fluid.
D’Avino et al.(2015) found that the fluid elasticity enhances the deviations between the fluid and particle partitioning and the shear-thinning fluid does not show any significant deviation from the Newtonian case.
Most of the previous works have focused on the effect of non-Newtonian carrier fluid rheology on the motion of a single particle in bifurcating channels. The shear-induced particle migration which is important in concentrated suspensions has received much less attention in such geometries. Since the hydrodynamic interactions between the particles play an important role in the distribution of the particles, the fluid-particle partitioning between the downstream branches for concentrated suspension will not be the same as in the dilute limit. Motivated by the need to have a clear understanding of the effect of suspending fluid rheology on the shear-induced migration phenomenon and fluid-particle partitioning between the downstream branches, the study of suspension