23 research outputs found

    Experimental study of the bubble formation in T-Y junction micro-mixers

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    International audienceThe aim of this study is to investigate the bubble formation in different liquids within three types of gas-liquid micro-mixer geometries, including a T-junction and two Y-junctions. The bubble shape, size and formation mechanism were studied under various experimental conditions such as flow rates of both phases, physical properties of liquid and mixer's geometries. A micro-Particle Image Velocimetry (mu-PIV) technique and a high speed camera were used to characterize and quantify gas-liquid flows. It was revealed that the bubble formation, in particular the bubble size, depends on the geometry of the mixing section. A correlation gathering numerous experimental data was elaborated for the estimation of bubble size. The influence of different parameters like flow rate ratio between two phases, mixer geometry and surface tension is well taken into consideration based on the understanding of bubble formation mechanism at microscale. This paper marks an improvement in the domain where no global correlations were available in T and Y-junction devices, and this correlation is then an useful tool for micro-mixer design

    Étude locale et expérimentale des phénomènes interfaciaux

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    Ce travail est consacré à l'étude expérimentale des écoulements diphasiques et triphasiques d'inclusions (bulles, gouttes, sphères) en milieux tant newtoniens que non newtoniens à l'échelle microscopique et mésoscopique, en utilisant la visualisation par une caméra rapide, la vélocimétrie par images des particules (PIV) ainsi que la micro-vélocimétrie par images des particules. Des bulles et des gouttes ont été étudiées expérimentalement depuis leur formation, en passant par leur déformation jusqu'à leur coalescence. La formation de bulles dans des micro-mélangeurs a été étudiée et caractérisée par l'obtention de champs de vitesses. Différents paramètres, tels que le cisaillement, la géométrie de la zone de formation, les débits ou encore les propriétés physiques ont été testés afin de développer des lois d'échelles. La traversée d'une interface liquide-liquide par une inclusion a été abordée par des expériences originales, permettant de décrire la dynamique du phénomène, de définir des nombres adimensionnels et de mettre en évidence des instabilités interfaciales. L'effet Weissenberg a également été étudié aux différentes échelles afin de comprendre les phénomènes conduisant à son amplification. Enfin, en milieu viscoélastique et rhéofluidifiant, nous avons caractérisé l'écoulement autour d'une inclusion isolée solide par l'obtention de champs de vitesses. Ces résultats ont permis de confirmer l'origine viscoélastique du sillage négatif et de prédire ses caractéristiquesThe present work was devoted to the experimental study of the multiphase flow around inclusions in both Newtonian and non-Newtonian media at respectively microscopic and mesoscopic scales, by means of the Particle Image Velocimetry (both PIV and -PIV) and fast camera visualization. Bubbles and drops were experimentally studied starting from their formation, the rising and up to their coalescence and fragmentation. Bubble formation in micro-mixers was also investigated and characterized by measuring the liquid velocity fields. Different parameters, such as the shear rate, the geometry of the micro-mixer, the flow rates or the physical properties were tested to develop correlations of power-law kind. The deformation of a liquid-liquid interface due to the passage of an inclusion was investigated by original experiments in order to observe and describe the dynamics of the phenomenon, to define the reliable dimensionless numbers and also to highlight several interfacial instabilities. The Weissenberg effect was also studied at different scales in various non-Newtonian fluids in comparison with Newtonian fluids to understand the amplification phenomena under the combining effects of instability and normal forces. Finally, the flow around an isolated solid inclusion was characterized by performing the measurements of velocity fields in viscoelastic and shear-thinning fluids. These results were used to confirm the viscoelastic origin of the negative wake behind the solid sphere and to model its characteristicsNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

    Émulsification en systèmes microstructurés

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    Cette thèse, intitulée Emulsification en systèmes microstructurés , s inscrit au sein de la tâche Emulsification contrôlée du projet européen IMPULSE. Deux micromélangeurs en acier inoxydable, un V-type et un Caterpillar, ont été testés en utilisant un pilote d émulsification continue. Ces dispositifs conçus en acier inoxydable et fonctionnant comme des boîtes noires, des micromélangeurs transparents ont ensuite été utilisés afin de comprendre leurs mécanismes d émulsification. Les paramètres-clés intervenant dans la formation de gouttes à un orifice à l échelle macroscopique ont dans un premier temps été identifiés. A l échelle microscopique, la formation des gouttelettes dans le micromélangeur V-type est issue de la mise en contact des jets des phases aqueuse et organique formés à la sortie de ce dispositif et d un phénomène élongationnel avec des instabilités interfaciales. Dans le cas du Caterpillar, la taille des gouttelettes dépend de la géométrie interne des éléments en série de ce micromélangeur. La formation des gouttelettes est issue d un phénomène de cisaillement au niveau de la jonction en Y. La réduction de la taille de ces gouttelettes est ensuite due à leur passage dans les éléments de mélange. L utilisation de micromélangeurs transparents a, quant à elle, permis de caractériser davantage ces deux micromélangeurs par micro-PIV et caméra rapide. Enfin, une dépendance du diamètre des gouttelettes par rapport à l énergie dissipée est constatée pour le Caterpillar mais par pour le V-type. L énergie dissipée dans ces deux micromélangeurs semble être moindre et les émulsions formées de meilleure qualité par rapport aux procédés classiques d émulsificationThis thesis, entitled Emulsification in micromixers was carried out within the framework of the Task Controlled Emulsification of the European IMPULSE project. Two micromixers in stainless steel, the V-type and the Caterpillar, were tested in an experimental setup. These microdevices working as black boxes, transparent micromixers were used after to gain insight into the fundamental mechanisms for emulsification. Firstly, the key parameters enabling the drop formation at macroscopic scale were identified. At microscopic scale, the droplet formation in the V-type micromixer results from the contact of aqueous and organic phases jets at the outlet of the microdevice and from elongational phenomena with interfacial instabilities. In the case of the Caterpillar, the droplets size depends on the internal geometry of the microdevice. The droplet formation can be mainly attributed to the shearing phenomena at the Y-junction. The decrease of the droplets size is then due to their passage through the mixing elements in series in the outlet channel. Moreover, the use of transparent micromixers allows to characterize these two micromixers by the micro-PIV and high speed camera. A straightforward relationship between the energy dissipation and the size of droplets was established for the Caterpillar, but not for the V-type. Moreover, the energy dissipation within these two micromixers is lower and the emulsions obtained having a more satisfactory quality than in the case of the classical emulsification processesNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

    Multiscale hydrodynamic investigation to enhance the biogas production in upflow anaerobic reactors

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    European Biotechnology Congress, Comenius Univ, Bratislava, SLOVAKIA, MAY 16-18, 2013International audienceno abstrac

    Procédé de traitement anaérobie des boues et de valorisation du biogaz

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    Ce travail vise à développer une approche originale à micro et à méso-échelle pour étudier divers phénomènes et intensifier les performances du réacteur. A méso-échelle, l'accent est mis sur l'efficacité de la production de biogaz dans un réacteur anaérobie 2D sous différentes conditions hydrodynamiques ainsi qu à différentes concentrations de substrat. Puis, dans un dispositif microfluidique transparent, une seule granule de différentes tailles a été utilisée sous différentes conditions d'exploitation. Les effets des différentes conditions hydrodynamiques et des concentrations de substrat associés à la taille et la densité des granules de boues sur la production de biogaz ont été étudiésThe present work is focused on developing an original micro to mesoscale approach to investigate various phenomena and then to intensify the performance of a reactor. At mesoscale, the emphasis is given to the interactions between granular sludge particles as well as the biogas production efficiency in a 2D reactor under various hydrodynamic conditions at different concentrations of substrate. Then, within the microdevices, a single sludge particle of various sizes was used under different operating conditions such as superficial liquid velocity and concentration of substrate. The effect of different hydrodynamic conditions and concentration of substrate was studiedNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

    Current density distribution and gas volume fraction in the gap of lantern blade electrodes

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    International audienceElectrochemical processes involving gas evolution at appreciable rates have been optimized in their design for the sake of reduced energy consumption. The present investigation was conducted in view to reducing the energy demand of a pilot process for electrolytic reduction of hematite particles to iron metal; attention was paid at the design of the lantern blade anodes where oxygen evolution occurs. An experimental cell consisting on two facing anodes and two remote cathodes has been designed and used for investigation of the gas behavior and current density distribution at the anode blades. The model for prediction of secondary distributions was validated by measurement of the currents at the segmented anodes and the effects of the average current density and the anode gap could be observed. The model was finally applied to the pilot cell for iron production; as expected, larger gaps allow more uniform current distributions at the anode, however without reducing the cell voltage. In contrast, blade lengths in the order of 10-15 x 10(-3) m only would allow visible reduction in the cell voltage

    Experimental investigation of bubble and drop formation at submerged orifices

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    The aim of this study was to investigate bubble/drop formation at a single submerged orifice in stagnant Newtonian fluids and to gain qualitative understanding of the formation mechanism. The effects of various governing parameters were studied. Formation behavior of bubbles and drops in Newtonian aqueous solutions were investigated experimentally under different operating conditions with various orifices. The results show that the volume of the detached dispersed phase (bubble or drop) increases with the viscosity of the continuous phase (or dispersion medium), surface tension, orifice diameter, and dispersed phase flow rate. A PIV system was employed to measure the velocity flow field quantitatively during the bubble/drop formation, giving interesting information useful for the elucidation of the fundamental formation process at the orifice. It was revealed that the orifice shape strongly influences the size of the bubble formed. Furthermore, based on a simple mass balance, a general correlation successfully predicting both bubble and drop sizes has been proposed

    Growth of Microalgae-Bacteria Flocs for Nutrient Recycling from Digestate and Liquid Slurry and Methane Production by Anaerobic Digestion

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    Biogas production by anaerobic digestion from different wastes represents a growing interest in the panel of renewable energy. Digestate has already been a subject of numerous studies as part of microalgal culturing because it is still rich in nutrients. This study wants to use it as a reference to investigate the possibility to exploit Slurry for the same applications. The first part of this research aims to evaluate microalgae-bacterial flocs growth for nutrient recycling from liquid digestate and slurry, working at three different dilutions (10%, 30%, and 50%) of these two substrates, in order to determine the best value for nutrients and pollutants removal (ammonia and chemical oxygen demand removal rate) and microalgae-bacterial biomass production (autotrophic index). The best dilutions were 30% for digestate and 10% for slurry, allowing the highest ammonia and chemical oxygen demand removal rates. The second part evaluated methane production during anaerobic digestion at different ratios of substrate/inoculum (0.2, 0.5, and 0.8), using microalgae-bacterial flocs as a substrate and digestate or slurry as the inoculum. After 30 days, the anaerobic digestion without flocs showed the best performance compared to digestion with flocs (726.7 mL CH4·g−1 slurry, 245.6 mL CH4·g−1 digestate), whereas, for flocs digestion, the best ratio for both inocula was 0.2 substrate/inoculum with 317.2 mL CH4·g−1 slurry and 165.7 mL CH4·g−1 digestate. All solid masses are expressed in terms of volatile solids (VS)

    Growth of Microalgae-Bacteria Flocs for Nutrient Recycling from Digestate and Liquid Slurry and Methane Production by Anaerobic Digestion

    No full text
    Biogas production by anaerobic digestion from different wastes represents a growing interest in the panel of renewable energy. Digestate has already been a subject of numerous studies as part of microalgal culturing because it is still rich in nutrients. This study wants to use it as a reference to investigate the possibility to exploit Slurry for the same applications. The first part of this research aims to evaluate microalgae-bacterial flocs growth for nutrient recycling from liquid digestate and slurry, working at three different dilutions (10%, 30%, and 50%) of these two substrates, in order to determine the best value for nutrients and pollutants removal (ammonia and chemical oxygen demand removal rate) and microalgae-bacterial biomass production (autotrophic index). The best dilutions were 30% for digestate and 10% for slurry, allowing the highest ammonia and chemical oxygen demand removal rates. The second part evaluated methane production during anaerobic digestion at different ratios of substrate/inoculum (0.2, 0.5, and 0.8), using microalgae-bacterial flocs as a substrate and digestate or slurry as the inoculum. After 30 days, the anaerobic digestion without flocs showed the best performance compared to digestion with flocs (726.7 mL CH4·g−1 slurry, 245.6 mL CH4·g−1 digestate), whereas, for flocs digestion, the best ratio for both inocula was 0.2 substrate/inoculum with 317.2 mL CH4·g−1 slurry and 165.7 mL CH4·g−1 digestate. All solid masses are expressed in terms of volatile solids (VS)
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