Swirl number in helically coiled tube flocculators: theoretical, experimental, and CFD modeling analysis

This paper presents original results of theoretical, experimental, and computational fluid dynamics (CFD) modeling studies of helically coiled tube flocculators, using a parameter capable of representing hydrodynamic characteristics in these reactors. The absence of parameters that satisfactorily depict the relationship between axial velocity and secondary flow in helically coiled tubes requires the creation of new parameters and/or the determination of the adequacy of existing parameters. The theoretical adequacy in the formulation of the swirl number (SN) that is applicable to helical units is proposed in this paper; we aim to represent their hydrodynamic characteristics, which are not possible with the current formulation. This parameter is obtained using three-dimensional CFD modeling in 48 units with various hydraulic and geometric characteristics. Acting as flocculators, these 48 units are evaluated by experimental modeling, assessing an important parameter of the flocculation process—turbidity removal efficiency (TRE). The results demonstrate, for the first time, the relationship between TRE and the SN, making possible an improvement in projects of helical units, optimizing hydraulic and geometric characteristics to achieve high operational performance units.