Experimental and Numerical Approach to Enlargement of Performance of Primary Settling Tanks

Circulation regions always exist in settling tanks. These regions would result in short-circuiting enlargement of the dead zone and high flow mixing problems and avoid optimal particle sedimentation. Therefore, the main objective of the tank design process is to avoid formation of the circulation zone, which is known as dead zone. Experiments show that the tank performance can be improved by altering the geometry of the tank which leads to a different velocity distributions and flow patterns. In this paper, the presence of a baffle and its effect on the hydrodynamics of the flow field has been investigated in a primary settling tank. Hydrodynamics of the flow field in these basins is sophisticated. Therefore a numerical simulation has been provided to discover such flow field. Then, the flow structure was simulated by an unsteady two-phase finite volume method, with VOF (Volume of Fluid) model. Besides, the RNG turbulence model was used in the numerical calculations. Successively, in order to validate the mentioned method and for a better understanding of the phenomenon, experimental tests have been carried out using ADV (Acoustic Doppler Velocimeter) and a 0.2 m breadth rectangular model tank. Results depict the ability of this model in predicting the velocity profiles and circulation districts. Eventually, the optimum position of the baffle for enhancing the performance of the primary settling tank was determined by applying the above mentioned numerical scheme