Browsing by Author "Veerapaneni, Srinivas"

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    Filtration of polydisperse suspensions
    (1991) Veerapaneni, Srinivas; Wiesner, Mark R.
    The effect of polydispersivity of the influent suspension on the ripening stage of a granular media filter has been studied experimentally. Suspensions of spherical latex particles of sizes 0.09$\mu$m, 0.944$\mu$m and 7.04$\mu$m were filtered through a porous bed of glass spheres, under well controlled physical and chemical conditions. Effluent concentrations and headloss development were monitored. The presence of small particles is observed to improve the removal of large particles, while the removal of small particles is not enhanced by the presence of large particles. Relative particle removal appears to be predictable based on the surface area available in the bed for deposition to take place. Deposition morphology and relative distribution of the mass in the bed play an important role in headloss development during filtration of polydisperse suspensions. If smaller particles are present in the filter influent, the practice of "filter to waste" should improve the initial removal of particles near 1$\mu$m in diameter that might otherwise be poorly removed by clean filter beds.
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    Formation and morphology of colloidal deposits in porous media
    (1996) Veerapaneni, Srinivas; Wiesner, Mark R.
    The effects of physical parameters such as fluid velocity, particle size and influent particle concentration on the morphology of colloidal deposits, removal efficiency and head loss development in porous media are investigated. Monte Carlo (MC) simulations of colloid deposition on a one-dimensional permeable surface from a uniform flow field and on an impermeable one-dimensional surface in plane stagnation flow are performed. Simulation results indicate that (i) the morphology of the deposits formed in uniform flow field vary from open porous structure for small particles and low fluid velocities to compact structure with increase in particle size and fluid velocity and, (ii) the shape and structure of deposits formed in stagnation flow strongly depend on particle size and fluid velocity. At low velocities in stagnation flow, large particles form compact deposits while small particles form open porous structures. At high velocities, large particles form unstable pillar-like structure with fewer particles quickly building up the height of the deposit while smaller particles form fewer and more dense columns. Experimental observations of monodispersed latex particles filtered through a bed of spherical glass beads indicated that at high flow rates, influent particle concentration did not appear to have significant effect on the removal efficiency of the packed beds or on the head loss development as a function of retained particle mass. At low flow rates ($<$0.1 cm/sec), most of the head loss was observed to occur in the top section of the bed. At high flow rates, the particle deposition was relatively more uniform along the depth of the bed. The fractal dimensions of the deposits was observed to vary from 1.6 to 2.4 with increasing fluid velocity from 0.002 to 0.4 cm/sec. A window of low fractal dimensions was observed at intermediate flow rates (0.04-0.15 cm/sec). It is hypothesized that in this flow regime, deposits may have attained pillar-like structures, similar to those observed in simulations. The fractal dimensions of such columnar structures are expected to be low.