277545 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.