Simulation Study Of Flocculation Effect In DENSADEG

The DENSADEG is an external recirculation unit based on the lamellae settling principle.It is a fast,compact and adaptable unit,unaffected by variations in raw water composition and flow rate.It is necessary to study DENSADEG due to the design relies mainly on engineering experience,and the specific parameters have not been specified.Herein,based on the numerical simulation,the flow field in the DENSADEG with different scale are presented,and the results of flocculation caused by hydraulic retention time of the plug flow reaction zone is studied by observing the index of the vortex velocity gradients G₀ and G₀T,the results of flocculation caused by different geometry of draft tube and length of the water inlet are studied by observing the index of turbulent kinetic energy k and turbulent kinetic energy dissipation rate?in order to achieve the optimized design parameters of the DENSADEG.By analyzing the results of the simulation,it is obtained that the flocculation is affected by the different hydraulic retention time of the plug flow reaction zone when keeping other structural parameters as constants,the optimal hydraulic retention time is 4.5min⁵min.The optimal high of agitator tank h related to the effective depth H,it can be characterized through the ratio of h/H=0.59⁰.61.The optimal distance between the bottom edge of the draft tube and the bottom of the tank is dependent on the impeller's diameter.It is shown in detail that the optimal distance between the bottom edge of the draft tube and the bottom of the tank increases with the increment of the impeller's diameter.It also can be concluded that the flow turbulence intensity for the diversion angle of the draft tube 60ois more significant than the one of 45o,75oand 90o.By changing the length of the water inlet,it can be found that the uniformity of velocity distribution at the entrance had greatly affected.Therefore,the optimum flocculation and reasonable energy distribution can be achieved when setting the inlet pipe deep into the draft tube.The results of simulation provide reference values and practical guiding significance for the engineering design and operation of DENSADEG.