Se llevó a cabo una evaluación a escala real de las condiciones de mezcla y su influencia sobre la calidad del agua en un tanque de compensación del sistema de distribución de agua potable de la ciudad de Cali (Colombia). El estudio hidrodinámico con aplicación continua de trazador y mediciones de temperatura y de cloro residual libre para identificar el régimen de mezcla en su interior, tiempos de residencia, estratificación térmica y la variación del cloro en el agua almacenada, evidenciaron el comportamiento propio de un tanque de compensación. Se encontró además que la recirculación y el intercambio insuficiente de agua, los bajos de flujo de momento asociados a caudales pequeños y la estratificación térmica puntual pueden causar elevados tiempos de residencia en el tanque, altas edades del agua, mezcla insuficiente y pérdida importante del cloro residual libre. La metodología aplicada en este estudio es apropiada para la evaluación y optimización de tanques de compensación en sistemas de distribución de agua potable.

We performed a real scale evaluation of mixing conditions and its influence on water quality in a compensation tank of drinking-water distribution system located in the city of Cali, Colombia. The hydrodynamic study with continuous injection of tracer, and temperature and free chlorine measurements for identifying the mixing regime in the tank's interior, residence time, thermal stratification, and chlorine variations in the stored water showed the typical characteristics of a compensation tank. We concluded that water recirculation, inadequate water exchange, low moment fluxes associated with low velocity flows, and punctual thermal stratification could lead to high water age, high residence times in the tank, inadequate mixing, and important loss of free residual chlorine. The methodology developed is suitable for evaluation and optimization of compensation tanks of drinking water distribution systems.

Foram avaliadas em escala real, as condições de mistura e sua influência sobre a qualidade de água num tanque de compensação do sistema de distribuição de água de abastecimento da cidade de Cali (Colômbia). O estudo da hidrodinâmica com aplicação contínua de traçador y medições de temperatura e de cloro residual livre para identificar o regime de mistura no interior, tempos de residência, estratificação térmica e a variação do cloro na água armazenada, evidenciaram o comportamento próprio de um tanque de compensação. Encontrou-se também que a recirculação e o intercâmbio insuficiente da água, as quedas de fluxo de momento associadas a pequenas vazões e a estratificação térmica pontual, podem causar elevados tempos de residência no tanque, elevada idade da água, mistura insuficiente e perda importante do cloro residual livre. A metodologia aplicada neste estudo, é apropriada para a avaliação e otimização de tanques de compensação em sistemas de distribuição de água de abastecimento.

The present contribution describes three-dimensional Euler/Lagrange calculations of confined horizontal gas-particle flows (i.e. channel and pipe flows) emphasizing the importance of elementary processes, such as particle collisions with rough walls and inter-particle collisions, on the predicted overall flow pattern and pressure drop along the duct.

In this paper the transient threedimensional flow developing in a cylindrical laboratory bubble column is addressed from a numerical point of view. The simulation scheme combines a Large Eddy Simulation (LES) for describing the liquid phase and a Lagragian approach for the gas phase (discrete bubbles) phase. The bubble equation of motion considers all the relevant forces, i.e., buoyancy, fluid stresses, drag, added mass and transverse lift. From the calculations, the transverse lift in combination with the drag is identified as the main mechanism allowing the bubbles to spread over the column cross-section. The liquid and gas velocity profiles obtained are compared with experimental data and k - e results. As a matter of fact, the dynamic structure of the liquid flow induced by the rising bubbles is well reproduced and also good quantitative results for all measured variables of both phases, gas and liquid, are obtained.

Under certain conditions, a fully developed turbulent flow in a straight pipe may show a secondary flow; for instance, when non-circular cross-section or non-uniform wall roughness around the perimeter of the duct are considered. In horizontal pipe particle-laden gas flow, the non-uniform forcing of the flow by the solids entrained in the gas core may also drive a secondary flow, even with uniform wall roughness along the circumferential direction. In this paper, the effects of wall roughness, particle size and particle mass loading ratio on the secondary flow developing in a horizontal pipe of circular cross-section under turbulent conditions are analysed. The computations are based on the Euler-Lagrange approach accounting for wall roughness and inter-particle collisions (i.e., four-way coupling). In the case of inertial particles, if inter-particle collisions are disregarded, the secondary flow consists of two recirculation cells with an upward flow near the vertical (symmetry) axis and a downward flow close to the walls. On the other hand, when inter-particle collisions are accounted for, the pattern depends on the particle concentration profile: with relatively smooth walls (low roughness), two recirculation cells are found, but with rough walls four recirculation cells are generated. For smaller particles, a transition between two and four recirculation cells in the secondary flow is observed by increasing the mass loading ratio.

In this work, the pneumatic conveying of non-spherical isometric particles with different degrees of non-sphericity is studied. The solids mass loading fraction is small enough in order to have a dilute flow, so inter-particle collisions can be neglected. As a first approximation, only the aerodynamic drag force acting on the particles is considered, neglecting the lift forces and the particle rotation. The drag coefficient is calculated using the correlations of Haider and Levenspiel (1989) and Ganser (1993). The numerical simulations are compared with experimental data in a narrow six meters long horizontal channel flow laden with quartz and duroplastic particles with mean diameters of 185 and 240 mu m, respectively (Kussin, 2004).

This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993)), in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and Peirano (2001), which is based on the PDF approach and performs closure at the level of acceleration of the fluid experienced by the particle. Formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping the mathematical manipulation of the stochastic model simple, thereby avoiding some pitfalls and simplifying the derivation of macroscopic relations. The performance of both dispersion models is tested in the configurations of grid-generated turbulence (Wells and Stock (1983) experiments), simple shear flow (Hyland et al., 1999) and confined axisymmetric jet flow laden with solids (Hishida and Maeda (1987) experiments).