This study was conducted to evaluate the equity of the flow distribution to the flocculation basins. Several types of inlet structures of the open channel affecting the flow pattern and distribution trend were studied using the Computer Fluid Dynamics (CFD) simulation.
The inequitable flow distribution to the flocculation basin was an important problem faced in many water treatment plants. This inequitable distribution was related to the inlet structure and the flow behavior in the open channel. The traditional inlet structure introducing effluent from the pipe into the center of open channel resulted in significant inequitable distribution. In this type, the largest deviations in the basins and rows were 10.1% and 14.5%, respectively. The ratios of maximum to minimum discharges were 1.5 in the basins and 4.2 in the rows, respectively. In the structure having an elbow pipe with vertical outlet, the largest deviations were 10.5% in the basins and 5.5% in the rows, respectively. However, installing a baffle against the influent could significantly decrease the largest deviation less than 3% by reducing the approaching velocity. The side inflow introducing influent to the upstream end in parallel to the channel could improve distribution efficiency.
There was distribution error of 3% in computational results when using the step method and the CFD simulation. Generally, the open channel for the distribution was designed assuming plug flow and one-dimensional fluid behavior. However, the actual flow in the channel showed three-dimensional fluid behavior. When the channel was designed based on one-dimensional hydraulics, the distribution efficiency could not be obtained as expected.
Distribution error caused by the difference of inflow direction in design and actual structure was 7%. Therefore, the existing design method of open channel should be verified and corrected by three-dimensional analysis for the even flow distribution.
