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Towards improved understanding and optimization of the internal hydraulics of chlorine contact tanks




Taylor, Zachary H., author
Venayagamoorthy, S. Karan, advisor
Bledsoe, Brian, committee member
Wohl, Ellen, committee member

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The research presented in this thesis focuses on utilizing computational fluid dynamics (CFD) to further the understanding of the internal flow dynamics in chlorine contact tanks. In particular, we aim to address the following two critical questions: (1) for a given footprint of a serpentine chlorine contact tank with a fixed inlet configuration, how does the hydraulic efficiency of the tank depend on the configuration of internal baffles?, and (2) for water storage tanks modified for use as chlorine contact tanks, can inlet conditions be modified such that near plug flow conditions are induced close to the inlet and throughout the rest of the tank? Key design parameters were identified and parametrically tested for each of these design problems. For the serpentine baffle tanks, a benchmark contact tank geometry based on a scaled model of the Embsay chlorine contact tank in Yorkshire, England was used for validation and then subsequently modified by varying both the number and length of baffles. In order to define guidelines for hydraulically efficient baffle tanks, a parametric study consisting of forty high-resolution 3-D simulations of different tank configurations were performed to quantify the efficiency of the scaled contact tank as a function of the dimensional relationships between the inlet width, channel width, tank width, tank length, and baffle opening lengths. The simulations tested the hydraulic efficiencies of the different tank configurations. Hydraulic efficiency was quantified by the baffle factor (BF). We found that the most efficient tank had a BF of 0.71, and that hydraulic efficiency was optimized in this tank by maximizing the length to width ratio in baffle chambers and by minimizing flow separation through the tank, which was achieved by setting equal dimensions to the inlet width, channel width, and baffle opening length. A new contact tank geometry was then developed by applying the dimensional relationships that were shown by the parametric study to optimize BF, and by modifying the baffle geometries to minimize flow separation around baffle tips. The new contact tank design had a BF of 0.78, which represents a 10 percent improvement in hydraulic efficiency compared to the Embsay contact tank. In the study of inlet modifications for cylindrical storage tanks, inlet diffusers and inlet manifolds were developed and modeled. Experimental flow through curves (FTCs) of a benchmark storage tank used as a contact tank were used to validate the CFD model that was utilized in the study. Thirty-seven modified inlet configurations using two representative flow rates were modeled. The inlet manifolds improved BF significantly, whereas the inlet diffuser had insignificant effects. The key design parameters identified for the inlet manifold were the number of inlets and the height of the inlet(s) in the tank. The inlet manifold designed with 16 inlets with the inlet height set at 10 percent of the tank height improved the BF of the storage tank from 0.16 to 0.51. This 220 percent increase in BF represents a major improvement in hydraulic efficiency for such cylindrical contact tanks that are widely used by small water treatment systems.


2012 Spring.
Includes bibliographical references.

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