Numerical Modeling and Experimental Study of the Mechanical Flocculation Process

Flow characteristics are one of the main factors affecting the flocculation process. The flow field in the flocculation tank was numerically modeled using the κ-ε turbulent flow model by considering different hydraulic conditions such as the flow rate, paddle rotating speed, dimension and its installation positions. The numerical modeling and experiment observation indicates that the turbulent momentum κ and effective energy consumption ε can be used as an indicator of flocculation efficiency. The rectangular shaped flocculation tank can dampen the flow effectively, but in the four corners there is a lack of mixing, which can be solved by installing baffles to promote the flocs growth. A proper paddle rotating speed can increase the collisions between particles in the main flocculation area; while still keep the formatted flocs from being damaged by shear force. Increasing the paddle service range appropriately can enlarge the main flocculation area. The paddle installation height should consider the turbulent conditions in both the upper and lower part of the flocculation tank. A set of parameters was recommended for the mechanical flocculation tank design.