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Franck Pigeonneau - One of the best experts on this subject based on the ideXlab platform.

  • Experimental and numerical investigations of an oxygen single‐bubble shrinkage in a borosilicate Glass‐forming liquid doped with cerium oxide
    Journal of the American Ceramic Society, 2020
    Co-Authors: Luiz Pereira, Jaroslav Klouzek, Miroslava Vernerová, Annabelle Laplace, Franck Pigeonneau
    Abstract:

    The shrinkage of an oxygen single-bubble is investigated in a cerium-doped borosil-icate Glass Melt at 1150°C. Nine Glass samples are synthesized and investigated, utilizing three different amounts of Ce2O3 and three different redox ratios (Ce-(III)/Ce total). Employing in-situ observation, the single-bubble behavior is recorded with a camera. For each Glass Melt, five experiments are performed with different initial bubble radii. The shrinkage rate (da/dt) depends strongly on the cerium content as well as the redox ratio. Numerical calculations are also conducted to support the understanding of the bubble shrinkage mechanism in the given cases. The model adequately estimates the experimental data for several cases, and an explanation is proposed for the cases, in which it does not. Moreover, we demonstrate, physically and mathematically, the influence of the initial radius of the bubble on the mass transfer between the rising bubble and the Melt. We confirm the utilization of the "modified Péclet number", which is a dimensionless number that takes into consideration the influence of multivalent elements on mass transfer. Finally, we master the bubble shrinkage behavior by normalizing the experimental data employing a characteristic time for the mass transfer (&tau).

  • Coupled modelling of redox reactions and Glass Melt fining processes
    Glass Technology - European Journal of Glass Science and Technology Part A, 2007
    Co-Authors: Franck Pigeonneau
    Abstract:

    The quality of Glass depends upon the removal of dissolved gases and bubbles. A quantitative understanding of these processes is essential for Glass production today, where quality requirements are becoming increasingly stringent. Clas- sical fining involves adding an element or compound to the Melt which will, through oxidation–reduction reactions at high temperatures, produce gases that diffuse into the bubbles present in the Melt. The growth of these bubbles then enhances the rate of bubble removal from the Melt. The modelling of oxidation–reduction reactions and that of fining are generally treated independently from one another. However, due to the large number of bubbles present, a significant amount of dissolved gases are consumed and the chemical equilibrium in the Melt is changed. We present, in this paper, a theoretical model where redox equilibrium is coupled with bubble generation and growth. Our approach is similar to that proposed by Nemec and co-workers, but differs in the numerical method used. After a description of the model, we present the evolution of a bubble population with time and also apply the numerical method to an experimental tool where bubbling is used to equilibrate the partial pressures between the bubbles and between the Melt. The model results in an equilibrium time longer than that seen experimentally. The possible origins of the disagreement are investigated and discussed.

Gaël Varoquaux - One of the best experts on this subject based on the ideXlab platform.

  • In Situ Synchrotron Microtomography Reveals Multiple Reaction Pathways During Soda-Lime Glass Synthesis
    Journal of the American Ceramic Society, 2012
    Co-Authors: Emmanuelle Gouillart, Michael-j. Toplis, Julien Grynberg, Marie-hélène Chopinet, Elin Sondergard, Luc Salvo, Michel Suéry, Marco Di Michiel, Gaël Varoquaux
    Abstract:

    Ultrafast synchrotron microtomography has been used to study in situ and in real time the initial stages of silicate Glass Melt formation from crystalline granular raw materials. Significant and unexpected rearrangements of grains occur below the nominal eutectic temperature, and several drastically different solid-state reactions are observed to take place at different types of intergranular contacts. These reactions have a profound influence on the formation and composition of the liquids produced, and control the formation of heterogeneities.

André Thess - One of the best experts on this subject based on the ideXlab platform.

  • Chaotic mixing in electromagnetically controlled thermal convection of Glass Melt
    Chemical Engineering Science, 2010
    Co-Authors: Sugilal Gopalakrishnan, André Thess
    Abstract:

    A numerical investigation has been carried out to study the mixing behavior of electromagnetically controlled thermal convection of Glass Melt in a cylindrical crucible. Thermal convection caused by the internal heating of the Glass Melt is controlled by an external magnetic field applied along the axis of the crucible. Unlike in thermal convection without and with steady external magnetic fields, Lagrangian particle motion exhibits chaotic behavior in an oscillating magnetic field. The present study shows that the asymmetric thermal field caused by the gravitational body force is rotated in the clockwise and anticlockwise directions alternatively by the Lorentz force imposed by the oscillating magnetic field. As the magnetic field varies sinusoidally with time, the flow field undergoes periodic reorientation causing repeated stretching and folding of the material lines resulting in better mixing in the Glass Melt. The degree of mixing increases with the period of oscillation till it reaches a maximum and subsequently decreases with further increase in the period. A decline in the mixing performance is observed with increase in the magnetic field strength for a given period of oscillation. This is on account of the fact that the Lorentz forces try to nullify the asymmetry created by the gravitational body forces. The computational results presented here will be useful for developing better Glass homogenization systems.

  • numerical simulation of electromagnetically controlled thermal convection of Glass Melt in a crucible
    International Journal of Heat and Mass Transfer, 2009
    Co-Authors: C Giessler, André Thess
    Abstract:

    In this paper, we present a three-dimensional numerical study of Glass Melt in a small scale circular crucible heated by two rod electrodes. Lorentz forces are imposed into the Melt by applying an additional external magnetic field. The coupled non-linear conservation equations for mass, momentum, energy and electrical charge are solved with the commercial finite volume code FLUENT. We perform numerical parameter studies by varying the magnetic flux density and the electrode potential to verify the influence of the Lorentz force on the velocity and temperature distribution in the crucible. We observe that the Lorentz force leads to an overall increase of the kinetic energy. Especially below the electrodes, a region which is not affected by buoyancy, the Lorentz force increases the velocity significantly. If the Lorentz force is the dominating driving force the mean velocity is almost a linear function of the Lorentz force. For counteracting Lorentz force and buoyancy between the electrodes we find a discontinuous modification of the flow pattern during the transition from buoyancy dominated to a Lorentz force dominated flow regime and vice versa. Even more, we pass through a hysteresis and obtain two steady solutions for one set of parameters depending on the starting conditions. Furthermore, we identify regimes in which we have a significant improvement of the temperature homogenization. The results show that Lorentz forces provide a new way to influence thermally driven convection of molten Glass and can lead to the improvement of mixing.

  • Electromagnetic effects on Glass Melt flow in crucibles
    Glass Technology, 2008
    Co-Authors: U. Krieger, B Halbedel, D. Hülsenberg, André Thess
    Abstract:

    Knowledge and control of the vortex flow in Melting systems play an essential role in improving the homogenisation of Glass Melts. Although from a historical perspective the influence and effect of electromagnetic forces on the Melt flow is not a new technique it still has no industrial application. This paper addresses this alternative method resulting from the application of Lorentz forces. So called external Lorentz forces are generated by the interaction of an electric current density and a magnetic flux density realised by direct electric heating via electrodes and an external magnet system. Experimental results on the electromagnetic modification of the flow in stacked Melts in a crucible, using coloured and colourless Glass are presented. In addition the temperature fluctuations enabled the calculation of the velocity and the direction of the flow in the Melts by the application of cross-correlation. The results show an enhanced thermal homogeni sation of the Glass Melts by the external Lorentz forces and provide possibilities for the optimisation of Glass production using magneto-hydrodynamic effects.

Luiz Pereira - One of the best experts on this subject based on the ideXlab platform.

  • Experimental and numerical investigations of an oxygen single‐bubble shrinkage in a borosilicate Glass‐forming liquid doped with cerium oxide
    Journal of the American Ceramic Society, 2020
    Co-Authors: Luiz Pereira, Jaroslav Klouzek, Miroslava Vernerová, Annabelle Laplace, Franck Pigeonneau
    Abstract:

    The shrinkage of an oxygen single-bubble is investigated in a cerium-doped borosil-icate Glass Melt at 1150°C. Nine Glass samples are synthesized and investigated, utilizing three different amounts of Ce2O3 and three different redox ratios (Ce-(III)/Ce total). Employing in-situ observation, the single-bubble behavior is recorded with a camera. For each Glass Melt, five experiments are performed with different initial bubble radii. The shrinkage rate (da/dt) depends strongly on the cerium content as well as the redox ratio. Numerical calculations are also conducted to support the understanding of the bubble shrinkage mechanism in the given cases. The model adequately estimates the experimental data for several cases, and an explanation is proposed for the cases, in which it does not. Moreover, we demonstrate, physically and mathematically, the influence of the initial radius of the bubble on the mass transfer between the rising bubble and the Melt. We confirm the utilization of the "modified Péclet number", which is a dimensionless number that takes into consideration the influence of multivalent elements on mass transfer. Finally, we master the bubble shrinkage behavior by normalizing the experimental data employing a characteristic time for the mass transfer (&tau).

Jaroslav Klouzek - One of the best experts on this subject based on the ideXlab platform.

  • Experimental and numerical investigations of an oxygen single‐bubble shrinkage in a borosilicate Glass‐forming liquid doped with cerium oxide
    Journal of the American Ceramic Society, 2020
    Co-Authors: Luiz Pereira, Jaroslav Klouzek, Miroslava Vernerová, Annabelle Laplace, Franck Pigeonneau
    Abstract:

    The shrinkage of an oxygen single-bubble is investigated in a cerium-doped borosil-icate Glass Melt at 1150°C. Nine Glass samples are synthesized and investigated, utilizing three different amounts of Ce2O3 and three different redox ratios (Ce-(III)/Ce total). Employing in-situ observation, the single-bubble behavior is recorded with a camera. For each Glass Melt, five experiments are performed with different initial bubble radii. The shrinkage rate (da/dt) depends strongly on the cerium content as well as the redox ratio. Numerical calculations are also conducted to support the understanding of the bubble shrinkage mechanism in the given cases. The model adequately estimates the experimental data for several cases, and an explanation is proposed for the cases, in which it does not. Moreover, we demonstrate, physically and mathematically, the influence of the initial radius of the bubble on the mass transfer between the rising bubble and the Melt. We confirm the utilization of the "modified Péclet number", which is a dimensionless number that takes into consideration the influence of multivalent elements on mass transfer. Finally, we master the bubble shrinkage behavior by normalizing the experimental data employing a characteristic time for the mass transfer (&tau).

  • The optimal parameters of bubble centrifuging in Glass Melts
    Journal of Non-crystalline Solids, 2011
    Co-Authors: Vladislava Tonarová, Lubomír Němec, Jaroslav Klouzek
    Abstract:

    Abstract The mathematical model of a multicomponent bubble in a Glass Melt under the influence of gravitational and centrifugal fields has been applied in the model TV Glass. The optimal fining conditions have been examined in a rotating cylinder with the aim of determining their general features. All of the dependences between the bubble-removal time and the rotational velocity showed the region of bubble removal by centrifuging at low cylinder rotational velocities and the region of complete bubble dissolution when the rotation was intensive. The low rotational velocities, characterised by the minimal bubble-centrifuging time, appeared to be suitable for industrial application. Consequently, the influence of temperature, pressure and Glass-layer thickness on the value of the optimal rotational velocity and optimal fining time of small-critical bubbles has been investigated in detail in a Glass Melt containing fining agent. The significant role of temperature and minor role of pressure have been proved and the identical features of bubble removal have been identified in cylinders with different radii and filling by Glass but with the same average thickness of the Glass layer on the cylinder walls.

  • The measurement of oxygen partial pressure and characterisation of oxidation-reduction equilibria in Glass Melts
    1999
    Co-Authors: Jaroslav Klouzek, D. Rohanova
    Abstract:

    The measurement of oxygen partial pressure in Glass Melts by the method of reference Glass Melt is presented. The experimental procedure completed by the wet chemical analysis of the ratio Fe 2+ /Fe 3+ is used for the determination of equilibrium constant of iron in soda-lime-silica Glass Melt. Experimentally obtained values of oxygen partial pressure bring input data for the calculation procedure of redox equilibria in Glass Melt containing sulphate and iron. In addition, calculated temperature dependencies of oxygen partial pressure are verified by experimental values. The calculation example showing positive effect of Calumite addition in Glass batch to the efficiency of bubble refining process is discussed.

  • Determination of diffusion coefficients of gases in Glass Melts using the method of absorbed gas volume
    1995
    Co-Authors: Lubomir Nemec, Jaroslav Klouzek
    Abstract:

    The values of diffusion coefficients of gases in Glass Melt represent a significant quantity when studying refining process and kinetics of gas dissolving in Glass Melt. As the determination of gas concentration profiles in Glass is very difficult owing to the extremely low solubility of most gases in Glass, the method following the rate of absorption of given gas volume in Glass Melt using the high temperature visual method has been developed. Special mesuring vessels from silica Glass were applied to this purpose making it possible to follow the movement of phase boundary between measured gas and Glass Melt. The analysis of gas content of the measuring vessel after the experiment has been ensured. The equations were stated describing the absorption of pure gases as well as gas mixture into Melt. Using the method, the temperature dependences of D O2 and D H2O have been obtained for soda-lime-silica Glass in the temperature range 1200-1480°C