Experimental and Numerical Simulation of the Effect of Particles on Flow Structures in Secondary Sedimentation Tanks

Sedimentation tanks are designed for settling of floated solids in water flowing through the water treatment plants. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these systems. Flow pattern has an important role in the design and performance improvement of sedimentation tanks. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed. Kaolin was used as solid particles in these experiments. Also, a numerical simulation was developed using the finite volume method with a k-? turbulent model. The results of the numerical model agree well with the experimental data. Hydrodynamic parameters and flow patterns of the fresh water flow and particle-laden flow are also compared in this study. The results show that the existence of particles completely changes the flow structures. It seems that the main reason for this phenomenon is the particles settling. Our experimental observations and numerical results show that parameters such as the maximum streamwise velocity, fully developed location, shear stress coefficient at the bottom of the tank and so on are different in water-containing particles compared to pure water and the inlet concentration strongly intensifies the differences.