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Date of Award

2018

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Environmental Engineering (PhD)

Administrative Home Department

Department of Civil and Environmental Engineering

Advisor 1

Brian Barkdoll

Committee Member 1

Melanie Kueber Watkins

Committee Member 2

Pengfei Xue

Committee Member 3

Fernando Ponta

Abstract

Poor mixing in storage tanks can cause stagnant zones that could pose negative public health effects. To eliminate stagnant zones in a cylindrical water storage tank, this study investigated the feasibility of a novel internal piping configuration consisting of a sprinkler-type inlet piping that distributed the incoming flow evenly across the water surface and a corresponding upside-down sprinkler draining configuration at the tank bottom. The experiments were conducted on seven types of inlet and outlet configurations. Experiments were performed using an acoustic Doppler velocimeter (ADV) and electrical conductivity (EC) measurements. Various stagnation metrics, like the time for the water to be well-mixed and water particle velocity and direction, were employed for each configuration. In addition, a new metric is introduced to evaluate short circuiting conditions in storage tanks. Inlet/outlet convergence time is a simple indicator, in which the lower the value, the higher the risk of short-circuiting. In the next step, experiments were performed with a temperature difference between the tank and the inflow due to density-driven flows. Results indicated that the novel piping resulted in parallel downward streamlines that eliminated most of the stagnation zones in the tank.

Next, we studied life cycle assessment (LCA) of three options available to solve water stagnation in storage tanks. Using a 20-year period of time as a baseline for the manufacture and operation of mixer, multiple inlets, and sprinkler systems. These options were compared using different life cycle assessment (LCA) tools. Using SimaPro modeling software as well as IPCC 2013 GWP 100a V1.0, Cumulative Energy Demand methods, and Eco-indicator 99 these three types of mixing approaches were compared with and without waste recycling. In addition to the LCA, cost analysis showed that application of a sprinkler is the least expensive option. Damage- cost analyses for categories of human health, ecosystem quality and resources showed that a sprinkler caused the least damage and cost, while a mixer resulted in the most damage and cost.

Finally, in continuation of our previous studies to address this problem using sprinklers as the inlet and outlet, Computational Fluid Dynamics (CFD) modeling was used to investigate more cases and come up with design suggestions. The CFD modeling results using a K-ϵ model were verified with experimental results. Then, the sprinkler system was applied to a spherical tank and the results were compared with the same tank employing an angled-nozzle sprinkler system as the inlet. Results showed the superiority of the angled-nozzle sprinkler system. The introduction of different temperature water to the tank was used to measure the well-mixed time. Using this mixed-time indicator, the effect of height to diameter ratio (H/D) on cylindrical tanks employing a sprinkler system as their inlet and outlet was investigated and two equations were suggested for H/D less than and greater than 0.75, with the former resulting in faster mixing.

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