OPEN ACCESS
This paper aims to identify the optimal working effect of peripheral-inlet and outlet (PIO) circular secondary clarifiers (CSCs). For this purpose, the simplified multiphase mixture model was adopted for the 2D numerical simulation of hydraulic features of the solid-liquid two-phase flow in CSCs. Specifically, the closed-form time-averaged flow equations were established by the RNG k- ε turbulence model, the differential equations were discretized by the finite volume method, and the coupling velocity and pressure equations were solved by the pressure-implicit with splitting of operators (PISO) algorithm. Then, numerical simulations were performed to disclose how the retaining baffle-deflection baffle distance and retaining baffle depth influence the distribution of the velocity field and sludge volume concentration field in a PIO CSC. The simulation results show that the optimal performance of the CSC appeared at the baffle distance of 300mm and the retaining baffle depth of 600~1,000mm. All in all, a proper increase of distance and depth can enhance the sedimentation efficiency and outflow quality, but an excessive increase can only accomplish the very opposite. The research findings provide valuable references to the optimal design of actual secondary clarifiers.
circular secondary clarifier (CSC), peripheral inlet and outlet (PIO), numerical simulation, velocity field, sludge volume concentration field
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