Effets des anions minéraux sur la décomposition de l'ozone dans l'eau

L'influence des anions minéraux sur la décomposition de l'ozone est étudiée. Les expériences mettent en oeuvre les anions SO42-, PO43-, BO33-, SiO22-, NO3-, HCO3-+ CO32- à des concentrations identiques à celles habituellement rencontrées dans le domaine des eaux potables. Un plan d'expérience simple qui permet d'attribuer ou non une influence à chaque espèce minérale et de voir l'interaction éventuelle avec le pH est utilisé. Les manipulations sont réalisées sur un pilote de laboratoire conçu pour éliminer toutes traces de matières organiques.L'étude fait apparaître que seuls les carbonates et les bicarbonates ont une influence notable sur cette décomposition et que le pH interfère en jouant sur l'équilibre carbonates-bicarbonates. Ceci permet de vérifier l'équation théorique établie par YURTERI et GUROL (1988) en l'absence de matières organiques. L'ordre apparent de la réaction varie entre 1 et 2 : ordre 2 pour les teneurs en bicarbonates faibles (30 mg.l-1) et ordre 1 pour une teneur forte (300 mg.l-1) lorsque le pH basique déplace l'équilibre vers les carbonates. Pour 300 mg.l-1 et des pH neutres l'ordre de la réaction oscille entre 1,5 et 2. Pour un ordre 1, on peut calculer la constante d'initiation de la décomposition de l'oxydant par l'ion hydroxyle OH- (k = 80 l.mol-1 s-1).The influence of anionic mineral species on the decomposition of ozone in water was studied. The experiments involved the anions SO42-, PO43-, BO33-, SiO22-, NO3-, HCO3-+ CO32- at concentrations identical to those usually found in drinking water. The manipulations were carried out with a simple experimental procedure which allowed to determine whether or not the mineral species had an influence on this decomposition and to observe thereof the effect of the pH. A laboratory pilot made of glass and teflon, in order to eliminate any traces of organic compounds, was used.Results of this work prove that only the carbonates and bicarbonates have a notable influence on this decomposition and that the pH interferes by disrupting the bicarbonate-carbonate equilibrium. The theoretical equation established without organic compounds by YURTERI and GUROL (1988) is verified.The order of the reaction varies from 1 to 2. The order is 1 when the amount of bicarbonates is weak (30 mg/l). The order is 2 in the case of a 300 mg.l-1 concentration when the basic pH changes the equilibrium towards the carbonates. For 300 mg.l-1 concentrations and a neutral pH, the order of the reaction reaches values from 1,5 to 2. In the case of an order 1, the constant rate of the oxidant decomposition by hydroxyle ion OH¯ is calculated. Its value is 80 l.mol-1 s-1

Benchmarking and viability assessment of optical packet switching for metro networks

Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained

Benchmarking and viability assessment of optical packet switching for metro networks

Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained

Towards the design of an intensified coagulator

This study compares the hydrodynamics in three millimeter-scale continuous reactor geometries that can be easily used in laboratories and industries – a straight tube, a coiled tube and a Dean-Hex reactor – via numerical simulations and analyses the data in a way that is specifically relevant to coagulation processes, thereby offering insights for engineers to develop new coagulation reactors. A numerical approach based on Lagrangian particle tracking is presented to better understand the impact of the geometry and flow on properties that influence coagulation. The results show that the Dean-Hex meandering geometry provides narrower residence time and shear rate distributions, as well as higher mean average shear rates and Camp number distribution than the other geometries. This is attributed to the generation of transverse flows and radial mixing in the Dean-Hex reactor and suggests that a faster and more homogenous coagulation can be expected

Prevalence and associated risk factors of psychotic symptoms in homeless people in France:Abstract of the 25th European Congress of Psychiatry

<p>Miscellaneous classes: inconsistent studies of pregnancy-associated pharmacokinetic changes (percent calculated as pregnant/nonpregnant values).</p

Influence of gas flow rate on the structure of trailing vortices of a rushton turbine: PIV measurements and CFD simulations

Trailing vortices behind rotating impeller blades play crucial role in determining gas accumulation behind them. The gas accumulation behind blades affects the pumping and power dissipation capacity of the impeller and thus significantly affects the performance of gas-liquid stirred reactors. Understanding fluid dynamic characteristics of these trailing vortices and capability to computationally simulate these vortices is, therefore, essential for reliable design and scale-up of stirred reactors. In this paper, we have used particle image velocimetry (PIV) technique and CFD model based on computational snapshot approach for systematically studying influence of gas flow rate on structure of trailing vortices behind blades of a Rushton turbine. PIV measurements were carried out in a standard, fully baffled stirred vessel (H/T= 1) with a flat bottom. Vessel diameter was 0.4 m. A six bladed standard Rushton turbine was placed at one third of liquid height with a ring sparger. Four baffles of 1/10 T width were placed at equal spacing. Tap water was used as a medium in the vessel. Measurements were carried out at five different gas flow rates to vary the dimensionless gas flow number in the range of 0.01 to 0.06. Both, angle resolved and angle averaged flow fields near the impeller blades were measured. The structure of trailing vortices in presence of gas was studied in detail. A Eulerian-Eulerian, two fluid model was used to simulate dispersed gas-liquid flow in stirred vessel. A computational snapshot approach was used to simulate impeller rotation. The computational model was implemented using the commercial CFD code, FLUENT (of Fluent Inc., USA) with the help of user defined subroutines. The computational model was used to simulate flow in stirred vessel operating under conditions used in the experiments. The results of this study will have important implications for extending the applicability of CFD models for simulating multiphase stirred reactors

Trailing vortices of rushton turbine: PIV masurements and CFD simulations with snapshot approach

Understanding fluid dynamic characteristics of trailing vortices behind impeller blades and the capability to computationally simulate these vortices is essential for reliable design and scale-up of stirred reactors. In this paper, trailing vortices behind the blades of a standard Rushton turbine were studied using particle image velocimetry (PIV). Angle resolved and angle averaged flow fields near the impeller blades were measured and the structure of trailing vortices was studied in detail. A computational snapshot approach of Ranade and Dommeti was extended and used to simulate flow generated by the Rushton turbine in baffled stirred vessels. The approach was implemented using the commercial CFD code, FLUENT (of Fluent Inc, USA). Two turbulence models, namely, standard k - ε model and renormalization group version (RNG) of k - ε model were used for simulating the flow in stirred vessels. Predicted results were compared with the angle resolved PIV measurements to examine whether the computational model captures the flow structures around impeller blades. Predicted results were also compared with the angle averaged PIV data. Predicted gross flow characteristics like pumping number were also compared with the present and previously published experimental data. The results and conclusions drawn from this study will have important implications for extending the applicability of CFD models for simulating flow near impeller blades