Avaliação numérica da qualidade de mistura e identificação de zonas de estagnação e estratificação no interior de reservatórios de distribuição de água

Abstract

A significant reduction in the concentration of free residual chlorine (FRC) is one of the main concerns in water distribution systems, as it is a key factor in determining water potability. Factors such as prolonged residence time and the type of liquid mixing lead to the formation of stratification and stagnation zones, which contribute to FRC decay. To mitigate the issue of FRC decay in reservoirs and ensure compliance with water potability quality standards, this study aims to conduct a numerical analysis of mixing quality and the identification of stagnation zones within water reservoirs. The subject of this study is a semi-buried rectangular water storage reservoir. The methodologies employed involved modifying operational and design variables, which play a fundamental role in the formation of stagnation and stratification zones. An evaluation of the residence time for the liquid mixture was conducted, considering convective and diffusive aspects, as its determination is essential for validating the proposed modifications. The approach used numerical solvers, specifically computational fluid dynamics (CFD) techniques, to model the process and assess both quantitative and qualitative aspects of the flow inside the reservoir. For geometry construction, mesh modeling, numerical resolution, and post-processing of data, Ansys software was utilized. The findings of this study align with the literature, which highlights the ratio between the inlet and outlet areas as a determining factor in flow homogenization and in minimizing recirculation and stagnation zones. Configurations with a higher inlet-to-outlet (I/O) ratio promote a more uniform outflow, while configurations with a lower ratio can generate steeper pressure gradients and favor thermal stratification. Additionally, the analysis indicated that transient approaches could provide a more accurate representation of flow dynamics, as the steady-state model may limit the capture of effects such as turbulent oscillations and instabilities. Thus, the results of this study contribute to understanding the influence of geometric and operational parameters on flow behavior within reservoirs, demonstrating that optimizing these factors can enhance mixing efficiency and minimize undesirable effects such as stratification and stagnation zones. The application of computational fluid dynamics (CFD) proved to be a powerful tool for this analysis, enabling strategic adjustments to the system configuration.