Computational fluid dynamics application in modeling and improving the performance of a storage reservoir used as a contact chamber for microorganism inactivation

Abstract

This study explored the use of computational fluid dynamics (CFD) modeling approach to simulate two tracer studies conducted, in scaled-down physical models of an existing storage tank, to investigate the effect of tank configuration on the effective contact time (t 10 ). One of the scaled-down physical models, of the storage tank, was equipped with one baffle wall at the middle length and the other was equipped with nine baffle walls distributed evenly along the reservoir length. A comparison between the experimental and modeled tracer concentration profiles showed an excellent agreement. The developed CFD model was then applied to different reservoir configurations for further investigation towards achieving t 10 improvement. The use of seven small inlets and nine baffle walls resulted in extending the t 10 from about 8 min to about 30 min (for a theoretical detention time, τ , of 32 min). Furthermore, using fewer baffle walls with different inlet arrangements enhanced the t 10 .Résumé : La présente étude examine l'utilisation de la modélisation de la dynamique computationnelle des fluides pour simuler deux études à l'aide d'indicateurs, effectuées dans les modèles physiques réduits d'un réservoir de stockage existant, afin d'étudier l'effet de la configuration du réservoir sur le temps de contact efficace (t 10 ). L'un des modèles physiques réduits du réservoir de stockage a été muni d'un mur déflecteur au milieu de la longueur et l'un autre a été muni de neuf murs déflecteurs distribués également sur la longueur du réservoir. Une comparaison entre les profils de concentration à l'aide d'indicateurs modélisés et les profils expérimentaux a montré une excellente corrélation. Le modèle de dynamique computationnelle des fluides développé a été appliqué à différentes configurations de réservoir comme complément d'étude afin d'améliorer le t 10 . L'utilisation de sept petits points d'entrée et de neuf murs déflecteurs a permis d'allonger le t 10 d'environ huit minutes à environ 30 minutes (pour un temps de séjour théorique, τ , de 32 minutes). De plus, l'utilisation de moins de murs déflecteurs avec différents arrangements de points d'entrée a amélioré le t 10 .

Determination of conventional velocity gradient (G) using CFD technique for a pilot-scale flocculation system

“…These have the shape of an S-curve when plotted with respect to time, with a minimum of 0 and a maximum of 1 (Templeton et al 2006). The FTC analysis investigates the effect of the rotational speed on the hydrodynamic flow characteristics (Ta 1999;Choi et al 2004;Baawain et al 2006;Svrcek et al 2006;Templeton et al 2006;Zhang 2006;Stamou 2008). Tracer testing is considered as a reliable approach for determining the hydraulic performance of a water treatment reactor (Svrcek et al 2006).…”

“…PHOENICS, ANSYS FLUENT, ANSYS CFX, FLOW3D, Flo + + and STAR-CD (Versteeg & Malalasekara 1995). In water and wastewater treatment processes, it has been widely used in investigation and optimization of plant design and operations (Haarhofi & Van der Walt 2001; Baawain et al 2006;Templeton et al 2006;Stamou 2008) and in flow distribution calculations in distribution channels (Ta 1999;Baek et al 2005). Using CFX multiphase modelling approach, Zhang et al (2008) could show for the flrst time that multiple sampling strategies are essential for improved ozone residual monitoring and tracer testing for full-scale ozone disinfection process.…”

“…The strategy was to include a scalar transport equation for a conservative species of known mass fraction and solve numerically in an unsteady mode for a certain period of time (Ta 1999;Choi et al 2004;Baawain et al 2006;Zhang 2006;Stamou 2008). Accordingly, tracer mass fraction of 1.0 was introduced at the inlet at time (Í) = 0; possessing similar fluid property (density and viscosity) as that of water and with a mass diffusivity co-efficient of 1 x lO'^^m^s '.…”

A Hybrid Approach for Increasing Baffling Factors in Contact Tanks

“…Until recently, contact tank design has used empirically derived equations, physical studies, and loosely descriptive tables (Wilson & Venayagamoorthy 2010, USEPA 2003). Advances in numerical methods and processing power have made computational fluid dynamics (CFD) an invaluable tool for understanding the complex flow phenomena that occur within disinfection contactors, but it is not widely used by small systems because of its cost and complexity (Amini et al 2011, Rauen et al 2008, Baawain et al 2006, Khan et al 2006). A majority of small systems still rely on empirical tables presented in USEPA's enhanced surface water treatment rules for determining disinfection (USEPA 2003).…”

Laminar and turbulent regime changes in drinking water contact tanks

“…This unique wording by USEPA implies that plug flow may occur in both laminar and turbulent flow, despite the significant difference between these flows. Recent studies have shown that few systems achieve a uniform plug flow velocity field; however, those researchers studied only systems in which the flow regime was entirely turbulent (Amini et al, 2011; Zhang et al, 2011a; Zhang et al, 2011b; Baawain et al, 2006).…”