Numerical simulation studies of agitating paddle dependence on characteristics of the flow field in the mechanical-continuous-flow-stirred reactor for flocculation

• Published in: Desalination and water treatment 2020-04, Vol.183, p.30-41
• Main Authors: Yao, Meng, Ran, Zhiling, Chen, Ting, Wu, Qibao, Dong, Xiaoqing
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics (CFD); Flocculation; Mechanical-continuous-flow-stirred reactor; Turbulence
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2020.25181

The effect of stirring paddle on the flow field and particle development during the flocculation process has been investigated in a mechanical-continuous-flow-stirred reactor. Firstly, the model of different types of stirring paddles and a different combination of paddles installation height built. Then, turbulent flow fields generated under all conditions were predicted by computational fluid dynamics simulations, followed by a detailed discussion based on numerical data. The flow field velocity characteristics, turbulence characteristics, input power, cycling time and other parameters were used to evaluate the characterization of the flow field in the flocculation process. Results showed that paddle four oblique blades (α = 30°) have the shortest cycle time of water flow with the minimum input power, which provides conducive conditions for more collisions of particles and reducing the consumption of input energy. Furthermore, different installation heights of agitator paddle have a significant effect on water conditions. Results derived from the axial velocity cloud program stated paddle position set as combination 1 (H1/H are 60, 130, 60 in respective tank cell) could provide faster flow velocity and enough particle collision, which promoted aggregation of flocs. Relatively smaller H1/H set the former of whole reactor developed stronger turbulence to create for more vortex upward agitator blades to short cycling time. The interaction frequency between particles and paddle area was the largest and blade area is violent mixing, which is benefit of particle collision and improved flocculation effects. Based on these, appropriate paddle types and their installation height of mechanical-continuous-flow-stirred reactor should be designed to enhance particle collision and subsequent particle removal efficiency. The present study may provide meaningful insights for optimizing the design and operation of a mechanical-continuous-flow-stirred reactor for flocculation.