Particle deposition on an infinitely permeable surface dependence of deposit morphology on particle size
Monte Carlo simulations of colloid deposition on a one-dimensional permeable surface from a uniform flow field are reported. The effects of particle size, fluid velocity, and particle density on the transport of particles to the collector surface by fluid drag, gravity settling, and Brownian motion are described in terms of a Peclet number, NPe. For NPe ≤ 10-1.7 (small, near-neutrally buoyant particles and low fluid velocities) deposit morphology converges to one of diffusion-limited growth characterized by a fractal dimension, D, of approximately 1.7. Thus, small particles (<0.1 μm) and low fluid velocities favor the formation of loosely packed deposits characterized by small fractal dimensions. Deposit morphology is more compact and approaches the theoretical ballistic limit (D → 2) for large values of NPe (> 103) corresponding to larger particles and higher fluid velocities. However, the theoretical limit is not attained due to constraints imposed on the simulation lattice and deposit restructuring. For intermediate values of NPe (10-1.7 < NPe < 103), an empirical expression is presented for calculating D directly from NPe. Intermediate values of NPe correspond to conditions for particle transport typical of many natural and engineered systems including groundwater aquifers, reverse osmosis modules, and ultrafiltration membranes. Deposits containing particles of two different sizes resemble deposits formed from the smaller of the two particles alone if the transport of one or both of these particles is dominated by Brownian diffusion (small NPe). In contrast, shadowing produces fractal dimensions of deposits composed of ’ballistic’ particles of two different sizes that are smaller than those for deposits of either of the particles alone. © 1994 by Academic Press, Inc.
Veerapaneni, S; Wiesner, MR
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