Projet ANR-07-JCJC-0058 – DyBuMelt : Dynamics, growth and break-up of bubbles embedded in melted solids.
Programme : Jeunes chercheuses & jeunes chercheurs (JCJC) 2007
Année de financement : 2007
Coordinateur du projet : INSTITUT NATIONAL POLYTECHNIQUE DE TOULOUSE (INSTITUT NATIONAL POLYTECHNIQUE DE TOULOUSE)
Partenaires : Centre national de la recherche scientifique; Institut national polytechnique de Toulouse; Institut national polytechnique de Toulouse
Montant : 170000.0 euros
Date de début : 2007
Durée : 48 mois
Résumé : "We want to focus on problems encountered in industrial processes such as glass or metal production. Therefore, the members of the project come from academic labs in the fields of Chemical Engineering, Fluid Mechanics and Energetic. They are supplemented with industrial colleagues who know the state of the art in production processes and their shortcomings. -  The capacity of industrial processes of material production (glass, steel, plastics ...) is conditioned by numerous physical and chemical phenomena. Flows in chemical reactors, phase separators and heat exchangers are often complex, due to the presence of a dispersed phase (in the present project we focus only on bubbles). The spatial dispersion and the size distribution of the inclusions need to be precisely predicted when the design of the industrial device has to be optimized. In the project, we aim at investigating fundamental scientific issues which have been identified as severe shortcomings of industrial processes related to the presence of bubbles in molten solids (liquid glass, polymer or metal). -  The industrial partners are engaged in non-competitive markets and therefore can collaborate together with the academic groups to the scientific developments proposed in the project. -  From the three industrial processes of material production (glass, steal and polymer), we can extract two major classes of physical phenomena related to bubble dynamics in very viscous fluids: -  - Hydrodynamic interactions and bubble growth due to gas absorption in a liquid glass or melted polymer. -  - Entrainment of gas and bubble break-up in a liquid metal under jet impingement. -  All the three melted solids have a quasi-Newtonian behavior with a viscosity strongly evolving with the temperature and the chemical content of the melting. Hydrodynamic interactions in a dispersed suspension, mass transfer around a single bubble and chemical reactions of the refining process have been separately investigated in the literature but a complete fully coupled model has never been developed. Also, bubble break-up in very viscous fluids and extremely high surface tension (gas-liquid metal) has been rarely investigated and is still poorly understood. -  Regarding the problem of mass transfer in a swarm of bubbles, the major difficulties are related to the simultaneous predictions of the dispersion of the bubbles, advection of the chemical species in the bulk and dissolved gas production/consumption controlled by chemical equilibriums. The high viscosity of the fluid is a practical limitation because it delays the removal of bubbles from the bulk but it has also a fundamental implication on the physics of the interactions. -  Concerning gas jet impacting onto a liquid free surface, the questions are related to the rate of gas entrainment in the liquid and the size distribution of bubbles generated by break-up of the initial entrained large pocket. Due to the contrast of viscosity (gas vs. liquid metal), the flow may be turbulent in the gas and laminar in the bulk of the liquid. The objectives are on the one hand to implement turbulent two-phase flow models based on Large Eddy Simulation and Eulerian interface tracking for large scale bubbles. -  The project we described aims at studying and modelling the intricate phenomena of mass transfer leading to growth, hydrodynamic interactions and bubble generation in very viscous flows encountered in material production such as glass or metal. Solids in fusion are sites of chemical reaction and mass/energy transfers which control the growth rate of the bubbles. Large bubbles may break-up under the simultaneous influences of hydrodynamic and interfacial stresses leading to a complex size distribution. We want to focus on these two aspects of bubbly flows encountered in industrial context. -  We want to include in the simulation tools of Computational Fluid Dynamics the role of interfacial mass transfer in reacting flows. The development of numerical mod