1. Direct simulations of mixing and aggregation in dense solid-liquid suspensions
Jos Derksen & Radompon Sungkorn
Chemical & Materials Engineering
University of Alberta
Canada
10 min presentations incl q&a

2. The issue: mixing in flocculants
THE chance to mix flocculant in tailings
turbulent flow of a dense slurry in a pipe
how much pipe length do we need?
how to inject?
scale will matter (?)
GOAL
try to visualize and understand mixing mechanisms at fine length scales through simulation

3. The “scientific” issues
the need for a multi-scale approach
fluid mechanics: turbulence of a dense solid-liquid suspensions
resolution of small turbulent eddies & the solid particles
macro-scale
mass transport: spreading of the flocculant in the interstitial liquid
meso-scale
aggregation: modeling the sticking-together of solids in flocculant-rich regions

4. A few words on modeling & numerics
Lattice-Boltzmann method for solving the flow of interstitial fluid
3D, time-dependent
Explicitly resolve the solid-liquid interface: immersed boundary method
particle diameter typically 12 grid-spacings
Solve equations of linear and rotational motion for each sphere
forces & torques:
directly (and fully) coupled to hydrodynamics
plus gravity
hard-sphere collisions
Finite Volume approach to scalar transport (for mixing of flocculant in liquid)
fluid flow
particle motion
scalar

5. Aggregation modeling - shear flow example
attractive interaction between particles defined by a
square-well-potential
two parameters:  and vc
if vr < vc particles stick
sticky particles

6. Some sample (former) results
settling & flocculating suspension
particles colored by the aggregate size
turbulent flow over a granular bed
particles colored by their velocity g
scalar mixing in a micro solid-liquid fluid bed

7. Perspective / research plans
Generate dense, turbulent slurry flow
Study spreading rates of floculant in this flow as a function of
turbulence properties
particle size (relative to turbulence
length scales)
solids volume fraction
Simulate flocculation in quiescent suspensions
relate square-well potential to flocculant concentration
effects of (inhomogeneous) flocculant distributions