Three-dimensional numerical simulations are performed to evaluate the effect of porous\nbaffles on the efficiency of water treatment contact tanks. A second-order accurate numerical model\nis employed for the solutions of unsteady flow and tracer transport through the porous baffles. The\nflow through the porous medium is characterized while using the Darcy-Forchheimer relationship.\nLarge Eddy Simulation (LES) model is used to simulate the instantaneous mixing of the tracer in\nthe chambers of the contact tank. Three different porosities are considered to evaluate the effect of\nporosity on the hydraulic and mixing efficiencies of the contact tank. Simulated time-averaged flow\nfield shows that porous baffles that are placed at the entrance of each chamber could successfully\nmitigate short-circuiting and yield plug-flow conditions through the system for low porosities. Flow\nin the contact tank becomes laminar as the flow velocities decrease due to viscous effects and inertial\nresistance in the porous zone. For this case, the tracer is transported with bulk flow through the\nsystem and leaves the contact tank with a high peak seen in the Residence Time Distribution (RTD)\nplot. Porous layer increases the hydraulic efficiency of the conventional design from â??poorâ? to\nâ??goodâ? according to the baffling factor and increases the overall efficiency from â??compromisingâ? to\nâ??goodâ? according to the AD index. Comparison of the performance of the porous layer with the\npreviously developed slot-baffle design shows that the slot-baffle design increases the efficiency of\nthe tank with increasing dispersion effects, whereas the porous design increases hydraulic efficiency\nand reduces the dispersion effects. While the porous design reduces energy efficiency by 33% due\nto a drastic increase in drag in the flow through porous zone, the slot-baffle design increases the\nenergy efficiency of the conventional design by 67%.
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