The purpose of this study is to develop and validate a numerical tool for evaluating the performance of a settling basin regarding the trapping of suspended matter. The Euler-Lagrange approach was chosen to model the flow and sediment transport. The numerical model developed relies on the open source library OpenFOAM, enhanced with new particle/wall interaction conditions to limit sediment deposition in zones with favourable hydrodynamic conditions (shear stress, turbulent kinetic energy). In particular, a new relation is proposed for calculating the turbulent kinetic energy threshold as a function of the properties of each particle (diameter and density). The numerical model is compared to three experimental datasets taken from the literature and collected for scale models of basins. The comparison of the numerical and experimental results permits concluding on the model's capacity to predict the trapping of particles in a settling basin with an absolute error in the region of 5% when the sediment depositions occur over the entire bed. In the case of sediment depositions localised in preferential zones, their distribution is reproduced well by the model and trapping efficiency is evaluated with an absolute error in the region of 10% (excluding cases of particles with very low density).
Many facilities for urban drainage systems are equipped with a pipe overflow structure that can often be treated as a circular broad-crested weir. Thus it is possible to evaluate the overflow discharge through this device by measuring the water levels in the upstream tank and at the outlet of the pipe. In the present study, computational fluid dynamics (CFD) is used to determine a relationship between the discharge and the water levels upstream and downstream of the orifice for a range of diameters between 200 and 600 mm and a relative head up to 2. Over 50 numerical simulations are performed to take into account all the operating conditions of the system: free flow, submerged flow and pressurized flow. A regression is applied to the resulting data in order to obtain an orifice equation valid in both free-flow and submerged-flow regimes. Specific formulas, derived from Bernoulli's theorem, are also given for pressurized flows. The proposed methodology is applied to two examples. ARTICLE HISTORY
The producers of dairy products must control the final quality of products by evaluating their textures. Certain devices on production lines such as heat exchangers cause texture losses, affecting product consistency. The mechanical stress due to plate heat exchangers is often at the origin of this change, although evaluations of products as they flow through heat exchangers are lacking. This work proposes a coupled approach to determine texture loss for yoghurt in a heat exchanger using rheological measurements and a Computational Fluid Dynamics approach. The results are based on the quantification of mechanical stress and compared with experimental measurements performed to evaluate texture loss in yoghurt samples. Practical applications The objective of this work is to optimize the production lines for dairy products such as yoghurts. To date, texture losses appear during their manufacture, resulting in a decrease in viscosity compared with the desired quality on the final product. By describing the behavior of yoghurt in a plate heat exchanger, the Computational Fluid Dynamics can diagnose mechanical stress and provide information that producers cannot access to improve their process. The work was carried out on a laboratory plate heat exchanger, which was used to select the yoghurt cultures used to produce the finished product. Simulations bring mechanical stress information to producers. They can thus correlate it to the loss of texture. The aim is to be able to reproduce this mechanical stress with devices other than the plate heat exchanger, but by first evaluating by modeling the mechanical stress to be applied.
L'objectif de cette étude est le développement et la validation d'un outil numérique permettant d'évaluer la performance d'un ouvrage de décantation vis-à-vis de l'abattement des matières en suspension. L'approche Euler-Lagrange est retenue pour la modélisation de l'écoulement et du transport solide. Le modèle numérique développé s'appuie sur la bibliothèque open-source OpenFOAM®, enrichie de nouvelles conditions d'interaction particule/paroi afin de restreindre le dépôt aux zones présentant des conditions hydrodynamiques favorables. En particulier, une nouvelle relation est proposée pour le calcul de l'énergie cinétique turbulente seuil en fonction des propriétés de chaque particule. Le modèle numérique est confronté à trois jeux de données expérimentales issues de la littérature et collectées sur des modèles réduits de bassin. L'ensemble de ces expérimentations permettent d'investiguer une large gamme des paramètres représentatifs de l'écoulement (nombres de Froude et de Reynolds) et du transport solide (diamètre adimensionnel). La comparaison des résultats numériques et expérimentaux permet de conclure sur la capacité du modèle à prévoir l'abattement avec une erreur absolue de l'ordre de 5% lorsque les dépôts ont lieu sur l'ensemble du fond. Dans le cas de dépôts localisés dans des zones préférentielles, la répartition des dépôts est bien reproduite par le modèle et l'abattement est évalué avec une erreur absolue de l'ordre de 10% (hors cas de particules très peu denses). Mots-clés : Suivi de particules ; transport solide ; dépôt ; matières en suspension ; CFD Settling efficiency of storm-water tanks using 3D modelling ABSTRACT.-The purpose of this study is to develop and validate a numerical tool for evaluating the performance of a settling basin regarding the trapping of suspended matter. The Euler-Lagrange approach was chosen to model the flow and sediment transport. The numerical model developed relies on the open source library OpenFOAM®, enhanced with new particle/wall interaction conditions to limit sediment deposition in zones with favourable hydrodynamic conditions. In particular, a new relation is proposed for calculating the turbulent kinetic energy threshold as a function of the properties of each particle. The numerical model is compared to three experimental datasets taken from the literature and collected for scale models of basins. The comparison of the numerical and experimental results permits concluding on the model's capacity to predict the trapping of particles in a settling basin with an absolute error in the region of 5% when the sediment depositions occur over the entire bed. In the case of sediment depositions localised in preferential zones, their distribution is reproduced well by the model and trapping efficiency is evaluated with an absolute error in the region of 10% (excluding cases of particles with very low density).
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