The Transport of Suspensions in Geological, Industrial and Biomedical Applications


Tunde

Babatunde Oguntade
tade@che.utexas.edu
Office: CPE 5.132
Phone: 512-471-7375

INTRODUCTION

Suspensions are dispersions of particles in a continuous medium and find expressions in a lot of natural and industrial settings including river flows or hyperpycanal turbidity currents, landslides, blood flow, paper manufacturing, food industry and petroleum industry. The abundance of suspension flows thus necessitates the need to understand their behavior in order to predict catastrophic behavior like landslides and design efficient suspension flow devices.

Most suspension flows display complex rheology like shear thinning, shear thickening and other non-Newtonian behavior with the observed rheological behavior being a consequence of the interplay between the hydrodynamics, stochastic, interparticle and body forces. The inability of the well developed Newtonian physics to model the behavior of suspensions and the computational inefficiency of discrete type models in describing suspension flows makes the development of continuum type methods inevitable. These macroscopic models must be tested by comparing their results to known experimental data in order to determine their limitations before they can be applied directly in engineering design.

It is necessary to point out that discrete models are still necessary to elucidate some phenomena occurring at time and length scales that cannot be resolved by macroscopic models. Specifically constitutive equations needed for the closure of macroscopic models and the effect of microstructure on rheology are easily derivable from discrete models.

My research can be broadly classified into three parts, which include the macroscopic modeling of dilute and concentrated suspensions and the effect of microstructure on observed rheology. The studies I have undertaken under these categories are described below.


DILUTE SUSPENSION TRANSPORT

Structure - morphology relationships in deltas

Involved the determination of the hydrodynamic conditions necessary for the steady progradation of deltas and the prediction of sedimentological details from seismic profiles using the shallow water equations for model description. I model the evolution of a river delta by assuming that the settling sediments from a dilute hyperpycnal current of thickness ho, velocity uo and particle volume fraction Co flowing down a shelf edge of thickness ηo onto the slope and then into the basin as shown in Fig. 1 is responsible for the formation and progradation of the delta.

figure 1
FIGURE 1. Schematic cross-section of a prograding river delta front showing the variables that describe the system.

Drug delivery from an arterial catheter

Determined the best design parameters for efficient systemic delivery of drugs encapsulated in nanovectors to arterial plaques from a catheter in terms of the width of injection (ω), the ratio of viscosity of the suspending fluid to that of blood (β), the ratio of the velocity of injection to that of blood and the bulk flow of blood (α), by solving the convection-diffusion equations and the Navier-Stokes momentum equations.

figure 2
FIGURE 2. Numerical solution of the model equations for system with a Pe = 713, α = 1, β = 0.1 and Da = ∞.  (a) Volume fraction of nanovectors; (b) dimensionless axial velocity distribution

CONCENTRATED SUSPENSION TRANSPORT

Particle phase distribution of pressure-driven flows of bidisperse suspensions

Investigated theoretically the pressure-driven flow of a suspension of buoyant bidisperse particles using the diffusion-flux (Shauly, Wachs & Nir, 2000) and suspension balance models (Nott and Brady, 1994) and compared the results to measurements from multi-frequency Electrical impedance tomography (EIT).

figure 3
FIGURE 3. Volume Fraction of PMMA distribution (a) Numerical solution of the isotropic suspension balance model (b) Electrical Impedance Tomography measurements of PMMA particles.

MICROSTRUCTURE STUDIES

Characterization of aging in drilling fluids by Brownian dynamics

Probed the microstructure from Brownian dynamics simulations of colloidal-like particles to determine the cause of aging in drilling fluids. Aging studies were carried as a function of particle concentration and wait time for both neutrally-buoyant and buoyant particles.

figure 4
FIGURE 4. Gel strength increase with time for a suspension of neutrally buoyant particles.

References

  1. Nott, P.R., Brady, J. F., 1994 Pressure-driven flow of suspensions: simulation and theory. J. Fluid Mech. 275, 157-199.
  2. Phung, T.N. 1993 Behavior of Concentrated Colloidal Suspensions by Stokesian Dynamics Simulation. PhD thesis, California Institute of Technology.
  3. Shauley A, Wachs,A.,Nir,A., 2000 Shear-Induced particle resuspension in settling polydisperse concentrated suspension , Int.J.Multiphase Flow 26, 1-14.