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Numerical Simulation of Particle Settling in Sedimentation Basins using the LES Model

Sattari, Reza | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50406 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firouzabadi, Bahar; Kazemzadeh Hannani, Siyamak
  7. Abstract:
  8. Sedimentation basins are one of the most important and costly processes of water treatment, in which the process of particle settling takes place using gravity. There are two types of sedimentation basins namely, primary and secondary basins. In the primary basins, due to the low concentration of particles, in simulation, it is possible to ignore the effect of particles on the equation of motion. But in the secondary type because of buoyancy forces (which is dependent on particle concentration), the particles affect the flow field. So far, various studies have been done on the simulation of sedimentation basins with numerical methods, but a comprehensive research on the simulation of secondary basins has not been carried out using LES turbulence method. In the present study, the numerical investigation of flow in two- dimension (using two-phase VOF method for free surface and turbulence model of RNG k-ε) and three-dimension (single-phase and LES method) in a secondary rectangular sedimentation basin has been provided with presence of particles and in the absence of particles. The OpenFOAM software are used to simulate the flow and a subroutine has been added to this software in order to model the effect of particles in flow field. Comparison of experimental results with this simulation show that using LES method is more accurate than k-ε model. Also, comparing the results of concentration obtained in the presence of particles with experimental results, reveals the importance of grain size and particle diameter variations respect to the average diameter of particles. The results show that bed slope from the outlet towards the tank entrance, decreases the maximum velocity and increases the settling time of particles, so that the efficiency of settlement is increased by 4% by 1% of bed slope. In addition, our calculations show that at low Froude and Reynolds numbers, the best entrance location is at the vicinity of free surface, however, for higher values of Froude and Reynolds numbers, the optimum entrance location would be at the middle of basin
  9. Keywords:
  10. Numerical Simulation ; Large Eddy Simulation (LES) ; Buoyancy Parameter ; Secondary Sedimentation Tanks ; Turbulent Model

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