(227d) CFD Analysis of the Convective Transport of Rod Shaped Particles in Cylindrical Pores

Rod-shaped bacteria and
non-spherical viruses are frequently encountered in membrane feed waters. Their
removal from drinking water supplies is essential to providing biologically
stable tap water, from wastewater before discharging to receiving water bodies
and to produce water free of viruses, cells, and cell debris during downstream
processing. The design of efficient
membrane separation systems to separate these pathogens requires an understanding
of the transport of non-spherical particles through porous
membranes. Previous modeling efforts have focused almost exclusively on
spherical particles.

In this research, computational fluid dynamics (CFD) has
been used to model the migration of rod- shaped particles in a cylindrical
pore. The analysis involves incorporation of both steric restrictions, which limit the positions and
orientations available to a rod in a pore, and hydrodynamic resistances
experienced by the particle because of the presence of the pore wall. Simulations
involved solving the Navier Stokes equation defined
in an Arbitrary Lagrangian Eulerian
(moving mesh) frame to predict the translational motion of a rod-shaped
particle at a fixed orientation where rotational motion of the particle was
neglected. The analysis yields the particle lag
coefficient, which is defined as the ratio of the particle velocity to the
fluid velocity when no particle is present. Using a centerline approximation,
particle reflection coefficients were determined by integrating the lag coefficient
over all sterically allowed
particle orientations.

In
all cases, including hydrodynamic resistances increased the particle reflection
coefficient relative to a model that only considered steric
limitations for rod shaped particles. Results obtained for particles with the
same rod diameter but different particle lengths (i.e., different aspect ratio)
shows that including hydrodynamic wall interactions in predictions of the
reflection coefficient has a larger impact for particles which are closer to
spherical (smaller aspect ratio) when compared to particles with greater aspect
ratios. Predictions of the reflection coefficient for different sized particles
with the same aspect ratio indicate that including hydrodynamic resistances has
a larger impact for smaller particles, with little difference between
predictions made with and without hydrodynamic resistances for particles larger
than ~ 50% of the pore size. 

CFD
simulations have also been performed with the inclusion of particle rotational
motion (i.e., torque). Results from these simulations will also be discussed in
this presentation.