Relação entre parâmetros hidrodinâmicos e segregação de fases em floculadores tubulares helicoidais

Abstract

Models for estimation of Efficiency of Turbidity Removal (ETR) in Helically Coiled Tube Flocculators (Portuguese acronym: FTHs) have been developed to support the understanding of the relationship between hydrodynamics and flocculation efficiency in FTHs. Nevertheless, in the context of developing such models there were no biphasic flow modelling, and, therefore, it was not possible visualizing and analyzing the solid-liquid flow behavior and phase segregation in the FTHs, generating scarcity of information about what is occurring inside of these units in terms of fluid-particle and particle-particle interaction. This scarcity leaves ETR estimation models with “black box” aspects regarding flocculation. In this context, this study sought to clarify the relationship between hydrodynamic parameters and phase segregation in FTHs, aiming to advance the understanding of flocculation in these units. For this, several configurations of FTHs were evaluated through computational fluid dynamics (CFD) modelling. In total, there were modeled 84 configurations considering single-phase flow and 54 configurations considering biphasic flow (solid-liquid). The hydrodynamic parameters studied were the Mean Velocity Gradient, the Mean Pressure Gradient and the Mean Specific Kinetic Energy. The solid phase was evaluated through the distribution of its volumetric concentration in the FTHs. Among the results, existing relationships between the hydrodynamic parameters, the volumetric concentration distribution of the solid phase and the ETR in the studied flocculators were identified and evaluated; it was verified a tendency that the greater the intensity of the secondary flow in the FTH, the greater the magnitude of the maximum volumetric concentration of the solid phase (CMax), which is close to the internal side of the curvature. Regarding the hydrodynamic parameters, there was a positive relationship between them and CMax; for the FTHs studied, it was verified that lower values of ETR were associated with higher values of the CMax. As a result of the acquired knowledge, it was proposed a new model for ETR estimative in FTHs. This model, in addition to producing fit statistics similar to the best performance available models, it is more parsimonious and all its parameters can be obtained through physical modeling, among other advantages.