Author(s): Dongjin Kim; Thorsten Stoesser; Jae-Hong Kim

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Keywords: Baffle spacing; contact tank; hydraulic efficiency indicators; internal recirculation; large-eddy simulation; residence time distribution; short-circuiting

Abstract: The effect of baffle spacing on the hydrodynamics and transport characteristics in a scaled variable-baffle-spacing contact tank is investigated by employing large-eddy simulation. Simulated solute transport is quantitatively validated by comparing simulated and measured residence time distribution curves, for which good agreement is found. The flow in serpentine disinfection tanks is dominated by a path of high streamwise velocities, a so-called short-circuiting path, which is almost constant in width regardless of the baffle spacing. In addition, large-scale turbulent vortices are shed from baffle edges and their size and dynamics depend on the spacing between subsequent baffles. The transport in serpentine-flow contact tanks is advection dominated and transport occurs mainly along the short-circuiting path. Wider compartments feature large recirculation zones with instantaneous vortices entraining solutes into these zones and thereby increasing residence times. Contact tanks with wide compartments suffer from severe short-circuiting and internal recirculation. This is directly reflected in hydraulic efficiency indicators.

DOI: https://doi.org/10.1080/00221686.2013.777681

Year: 2013