Keywords and Phrases
Hydrodynamics; Jet Mixing; Computational Fluid Dynamics (CFD); Buoyant jet; Stratification; Water Storage tanks; Variable volume; Multiphase flow; Aspect ratio; Turbulent jet
"The purpose of this study is to investigate the effects of different control variables on mixing in municipal water storage tanks using Computational Fluid Dynamics(CFD) solutions with ANSYS FLUENT for isothermal, positively and negatively buoyant inflow conditions. Poor mixing of old water and new water leads to dead zone formation, which when introduced in the distribution system can cause major water quality issues. Data for this study was generated using Multiphase CFD flow modeling technique using Volume of Fluid (VOF) approach with species transport. The vessel was considered to be mixed when Coefficient of Variation (COV) dropped below 0.10.
Results of isothermal flows show that for unity aspect ratio vessels, increase in momentum to eight times the baseline value cause a reduction of 67.7% reduction in the COV maximum value. With sufficient momentum, even tall vessels were found to mix. Positively buoyant inflow conditions are therefore uniformly desirable for mixing. Buoyancy was found to be a more dominant source of mixing than momentum. Negatively buoyant solutions indicate a very high dependance of mixing on buoyancy and hence are found to be undesirable to achieve uniform mixing. Results show that with increase in negative buoyancy effects, even at high velocities, the vessel was unmixed. At lower jet momentum and higher buoyancy effects, deadzones occupied more than 50% of the tank volume. Higher aspect ratio vessels are especially prone to stratification and poor mixing was generally observed with negatively buoyant inflows. Overall results reveal that some tanks which did not get mixed during the filling process got mixed in the hold cycle (inflow shutoff). A sufficient settling time is necessary after the fill duration to achieve the highest possible degree of mixing for a tank with a given momentum, aspect ratio and buoyancy"--Abstract, page iii.
Isaac, Kakkattukuzhy M.
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
Missouri University of Science and Technology
xv, 108 pages
© 2016 Pramod Narayan Bangalore, All rights reserved.
Thesis - Open Access
Library of Congress Subject Headings
Water -- Storage -- Quality
Computational fluid dynamics
Electronic OCLC #
Bangalore, Pramod Narayan, "Mixing dynamics in municipal water storage tanks" (2016). Masters Theses. 7548.