Rotating Filter Separator

• "Flow in a rotating membrane plasma separator," with A. Hajiloo, American Society for Artificial Internal Organs (ASAIO) Journal, 41:182-188, 1995. In this study we computationally modeled flow in a rotating filter separator using a commercial fluid dynamics code. The results correlate with our experiments showing that Taylor vortices translate axially at about the bulk axial velocity of the fluid. The radial velocities that arise from the Taylor vortex flow transfer fluid with high azimuthal momentum outward and fluid with low azimuthal momentum inward. More importantly, the structure of the axial transport of fluid depends on the ratio of Taylor number to axial Reynolds number. As the ratio increases, the flow consists primarily of axially translating Taylor vortices. As the ratio decreases, the Taylor vortices continue to translate, but they are smaller and much of the fluid winds around the vortices. We also found that the vortices die out at the downstream end of the annulus of a rotating filter because the Taylor number decreases as a result of an increase in viscosity as the particle concentration in the annular fluid grows as filtrate is removed.
  
  

• Current Research: We have recently embarked on an ambitious expansion of our work. For simplicity our past work considered only single-phase fluids. This approach was very successful in helping us understand the fundamental character of the flow. Our goal now is to examine the interaction between particles and the Taylor vortex flow to determine the character of the anti-plugging mechanism of a rotating filter separator. The centerpiece of the research is the simultaneous measurement of the motion of particles using Particle Tracking Velocimetry (PTV) and the velocity of fluid using Particle Image Velocimetry (PIV). Two different size particles will be used: relatively large particles to track the particle motion and very small particles to follow the fluid motion. To permit a high concentration of large particles without obscuring the optics, we use transparent particles with an index of refraction matched to that of the fluid. A small fraction of the particles are coated so that they are opaque. In this way the opaque particles can be tracked using PTV even at high particle concentrations to determine the motion of the particles. Using clear particles also permits the measurement of the fluid velocity using PIV simultaneous with the measurement of particle motion. This unique approach allows us to investigate the interaction between the fluid flow and the particle motion. In a second project, we are extending our stability analysis of circular Couette flow between differentially-rotating porous cylinders by adding an axial flow. Centrifugal Separation

• "Sedimentation of a suspension in a centrifugal field," with W. Hubler, Journal of Biomechanical Engineering, 113:485-491, 1991. To predict the spatial variation in concentration of a suspension with time during centrifugal separation, we developed an analytical model of the time history of sedimentation of particles in a centrifugal field for two geometries, a tube rotating about an axis perpendicular to its own axis and a cylindrical container rotating about its own axis. The Kynch theory for batch gravitational settling based on mass conservation was extended to include a centrifugal sedimentation force and cylindrical coordinates. Several other workers used methods similar to ours, but their analyses were only carried to providing characteristic curves. We carried the analysis further to obtain a physically useful result of concentration contours in the space-time plane. Our analysis results in a quasi-linear partial differential equation that was solved by the method of characteristics. The combination of radial dependence of the sedimentation force and cylindrical geometry causes several differences in the time-position history diagram of the sedimentation process compared to the standard gravitational case.