Numerical Simulation And Experimental Research In Mechanical Flocculation

G value is used to control the particle collision strength. However, the average velocity gradient is not a comprehensive reflection of the state of the reaction tanks. Flocculation tank design parameters are often empirically determined. However, the actual operation data suggest that some poor flocculation and high energy consumption. Therefore, researching the hydraulic characteristics of flocculation and its effect on the flocculation has important practical significance.The mechanical flocculation tank was selected to analysis different hydraulic conditions and its effect on the flocculation by conducting numerical simulation and coagulation test. The result can be to explore the hydraulic conditions of efficient flocculation.The conclusions of this paper are following:(1) The flow field in the flocculation tank was numerically modeled by considering different hydraulic conditions such as the flow rate, paddle rotating speed, dimension and its installation positions. The velocity distribution, turbulent kinetic energy κ and the turbulent dissipation rate ε and other dates of hydraulic characteristics were obtained by numerical simulation.(2) The equipment of mechanical flocculation was designed and fabricated to conduct coagulation test. Maintain a certain chemical factors such as raw water quality, temperature, dosage, and the experimental data of the supernatant water turbidity after20min settling were obtained by tests changing the hydraulic condition.(3) The turbulent kinetic energy, turbulent dissipation rate and residual turbidity were used as an indicator of flocculation efficiency. Increasing the hydraulic retention time can improve water turbulent quality to improve flocculation. A proper paddle rotating speed can increase the collisions between particles in the main flocculation area. The appropriate average κ value is proposed of0.0061～0.0021m2/s2, mean the average s value of0.0086-0.0019m2/s3. Increasing the paddle area will increase the main flow of the liquid and also increases the turbulent kinetic energy and turbulent dissipation. When the water contact area accounts for19.6%of the total cross section area, the paddle’s width to length ratio can be1/10or so, the flocculation effect is good. The turbulent state of the flocculation tank top and bottom should be taking into account for the placement of paddle height. The distance from the top of paddle board to the surface should be9.38%of total water depth of the first and third reaction tank, and the distance from the bottom paddle board to the bottom of the second reaction should be15.63%of total water depth, taking into account the paddle board to the bottom of the fluid movement, water turbidity is low.