| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 105 === This article presents a three dimensional Eulerian-Lagrangian model to simulate the enhanced sedimentation in an inclined vessel which called Boycott effect. The model solves the governing equation of fluid phase on the Eulerian mesh and calculate the motion of Lagrangian particles by Newton’s second law. In order to simulate the depositing particles at the wall, a soft-sphere collisional method is introduced so that the volume fraction reaches a random closed packing limit by the collisional mechanism. Additionally, Stokes’ drag, the previous drag model, is unsuitable for the denser suspension. A drag reduction model that considering the concentration of the fluid is employed. Ultimately, the two-phase model is capable of calculating the motion of fluid and particles in the dense flow.
This model is then used to study the Boycott effect. The result is validated against the PNK theory and agrees well with the theoretical values. The Kelvin-Helmholtz instability is observed during the settling process at different tilted angles. We find that the instability on the interface is related to the thickness of clear fluid layer. The greater the thickness of the clear fluid layer, the more stable the settling process is. Finally, the present work simulate under different parameters such as the diameter of the particles and the initial concentration of the flow field. While the diameter of particles are larger, the instability is weaker, and it leads to the better sedimentation efficiency. It also results in the same performance while setting the less concentration in the initial flow field. However, the effect of the tilted angle and the diameter of particles is more sensitive than the initial concentration. The simulation results show that Boycott effect does enhance the sedimentation in the inclined vessel or under tilted plates.
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