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Three-Dimensional Numerical Simulation in Rectangular Secondary Sedimentation Tanks Based on CFD

Author: YangLiLi
Tutor: WangXiaoLing
School: Tianjin University
Course: Environmental Engineering
Keywords: Advection secondary settling tank Computational Fluid Dynamics Euler solid-liquid two-phase flow Three-dimensional flow field distribution Distribution of suspended solids
CLC: X703
Type: Master's thesis
Year: 2007
Downloads: 160
Quote: 4
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Abstract


Secondary settling tank design is mainly based on the assumption that the ideal sedimentation tank, to determine the size of the secondary settling tank is very empirical, subjective and arbitrary. For this reason, it is necessary to state the secondary settling tanks and suspended solids flow concentration distribution studies to determine more precise secondary sedimentation tank size and precipitation efficiency, in order for the secondary sedimentation tank design and operation of management to provide a reference. At home and abroad on the basis of existing research, this paper established a two-phase model of Euler. Lieutenant particles as the fluid model proposed by improved high Reynolds number k-ε turbulence model and the solid phase turbulence simulation response function was introduced. The model takes into account the full impact of the solid-liquid interaction between the two phases, which are included in the interphase drag force, horizontal lift, virtual mass force and the volume fraction of the dispersed phase and the density difference between the dispersed and continuous phases influence; followed by the establishment of the secondary settling tank proposed single-phase three-dimensional flow model and simulate a certain amount into the water under the conditions of different secondary settling tank size distribution under the water and suspended solids. The finite volume method PISO algorithm in the secondary settling tanks advection dimensional fluid flow process were calculated and the experimental results with the Imam is verified by comparing the numerical simulation solution is correct. Simulation results show that: (1) the sludge hopper inlet below and above the recirculation zone exists; velocity distribution of the secondary settling tanks is non-uniform; wherein the width direction of the top of the water surface, respectively, from the center to both sides of the wall flow, the bottom surface of the water flow to the center, the center plane speed on a smaller, high-speed zone is mainly distributed in front of the secondary settling tank, sludge hopper near the top as well as the front. (2) exists near import bezel surrounding high concentration of suspended solids concentration region; in the middle of the secondary settling tank, the flow of suspension towards the top, bottom, top lower than the concentration of suspended solids; sludge hopper higher concentration of suspended matter. (3) the water inlet zone turbulent kinetic energy is large, while the precipitation area is very small, near the outlet turbulent kinetic energy increases. (4) inflow in certain conditions, the secondary settling tank baffle length, position on the secondary settling tank flow and concentration fields have some impact; suspended solids concentration is not high in the case of suspended solids particle size of the flow field not significantly affected, but the impact of the suspension on the distribution of the secondary settling tanks. (5) by simulating different secondary settling tank sizes inflow conditions are fixed and suspended solids flow distribution, the fit of the suspended solids removal and secondary settling tank length, width and height as a function of the relationship.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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