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Numerical Assessment of Optimum Baffle Configuration and Hydrodynamics of Settling Tanks

Asgharzadeh, Hafez | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40184 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi, Bahar
  7. Abstract:
  8. Sedimentation tanks are channels designed for sedimentation of suspended solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of water treatment plants. Therefore, researchers have tried to find better designs of sedimentation tanks. Among several design methods have been presented, modification of the geometry of tanks by installing baffles is one of the most effective and economic methods. According to the importance of performance improvement of industrial sedimentation tanks as well as the diversity in reported results, development and completion of previous studies seem to be necessary. In addition, a lack in physics of sedimentation in order to achieve deep understanding in this area and examining its effects on the hydrodynamics of sedimentation tanks is felt. In this work, flows containing suspended solids in a rectangular sedimentation tank are investigated and simulated by using finite volume method with k-ε turbulent model. While there is a good agreement between simulation and experimental results, the simulation results could be considered reliable. Besides, the simulation can be used as a predicting tool for other experiments that are barely possible or accessible in laboratory. The results reveal that particles completely change the flow hydrodynamic structure. Hydrodynamics parameters are totally different in particle laden water compared with pure water. From the view point of flow hydrodynamics, the baffle has significant effect on the flow pattern in sedimentation tanks. The influences of the baffle’s location on the flow pattern are also studied. Both of the baffles (baffle no. 1 and no.2 are located in the distance of 1.2 and 4 m from the entrance of tank, respectively) have noticeable effects on various parameters such as shear stress of the tank’s bed, height of the maximum velocity, magnitude of the maximum velocity in each section and consequently the overall removal efficiency of the tanks. In this manner installing a baffle and its location was useful in decreasing of the dead zone. Considering the outlet solid concentration, utilizing both of baffles was useful and they decreased outlet solid rate. Changes in inlet solid loading rate affect baffles function. According to the good agreement between simulation and experiment results, it was found that k-ε turbulent model is a proper model. In the present research, air shear layer effect on the free surface is considered with empirical equations. Nevertheless, air equations should be synchronously solved for achieving more logical results.

  9. Keywords:
  10. Numerical Simulation ; Particle Laden Underflow ; K-Epsilon Turbulence Model ; Settling Tank

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