Deposit morphology and head loss development in porous media

Experimental observations of monodispersed latex particles filtered through a bed of spherical glass beads indicated that flow ram plays an important role in head loss development by influencing the morphology of the deposits as well as the deposit distribution along the depth of the bad. The distribution of the deposits along the depth of porous media was more uniform at higher velocities. Deposits formed at low filtration (Darcy) velocities produced higher specific head loss (head loss per unit particle mass deposited) compared to the deposits formed at higher velocities. The fractal dimensions of the deposits formed in the porous medium varied with filtration velocity. The fractal dimensions of the deposits increased with increase in velocity at either end of the range of flow rate (0,002-0.4 cm/s) investigated. This is consistent with the low specific head losses observed at higher superficial velocities and with the theory of increasing fractal dimension as particle transport becomes more ballistic. The low fractal dimensions observed in the intermediate velocities (0.04 to approximately 0.15 cm/s) appear to be due to the formation of compact columnar structures. This conclusion was supported by Monte-Carlo simulations of colloid deposition from 2-D stagnation flow which were performed to approximate particle deposition at the top of filter grains.

Duke Scholars

Author Mark Wiesner Civil and Environmental Engineering