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Benjamin SOBAC


coordonnées


Ecole polytechnique de Bruxelles
Benjamin SOBAC
tel 02 650 29 45, fax 02 650 29 10, Benjamin.Sobac@ulb.ac.be
Campus du Solbosch
CP165/67, avenue F.D. Roosevelt 50, 1050 Bruxelles



unités de recherche


Centre Interdisciplinaire de Phénomènes Non-linéaires et de Systèmes Complexes [Center for Nonlinear Phenomena and Complex Systems] (Cenoli)
TIPs - Physique des fluides [TIPs - Fluid Physics] (TIPs - FLUIDs)



projets


Convection et échange de matière aux interfaces (ESA MAP-CIMEX) [Convection and Interfacial Mass Exchange (ESA MAP-CIMEX)]
Ce programme de recherche MAP (Microgravity Application Promotion) financé par l'Agence Spatiale Européenne et la Politique Scientifique Fédérale étudie les phénomènes de changement de phase et de transfert de matière à travers les interfaces liquide-gaz et liquide-liquide, ainsi que leur couplage avec les mouvements des fluides générés par la gravité et/ou la tension superficielle. Bien que l'essentiel de la recherche concerne l'évaporation, avec des applications en technologies de transfert de chaleur (refroidissement de composants électroniques) d'autres transferts sont également étudiés tels que l'absorption de gaz ou l'extraction de solvant, pour lesquels de nombreuses applications existent en Génie Chimique. En plus des études théoriques et numériques, des expériences sont réalisées non seulement en laboratoire, mais aussi en conditions de pesanteur réduite (vols paraboliques, fusée-sonde, satellites, station spatiale internationale). [This MAP (Microgravity Application Promotion) research program, funded by the European Space Agency and the Belgian Science Policy, studies phase change phenomena and mass transfer through liquid-gas and liquid-liquid interfaces, as well as their coupling with fluid motions induced by gravity and/or surface tension. While most of the research is on evaporation, with applications in heat transfer technologies (cooling of electronic components), other transfer phenomena are also studied such as gas absorption or solvant extraction, for which numerous applications exist in the field of chemical engineering. In addition to theoretical and numerical studies, experiments are realized, both in the laboratory and in reduced-gravity conditions (parabolic flights, sounding rockets, satellites, international space station). ]

Ebullition, transfert de chaleur et gestion des liquides - Influence de la gravité et des champs électrostatiques (ESA MAP-BOILING) [Boiling, heat transfer and fluids management - Gravity and electrostatic fields influence (ESA MAP-BOILING)]
Ce programme de recherches MAP (Microgravity Application Promotion) de l'Agence Spatiale Européenne associe plusieurs équipes européennes afin d'étudier les aspects fondamentaux et appliqués du phénomène d'ébullition. Plusieurs expériences en microgravité sont prévues, ce qui permet une compréhension plus fine de phénomènes qui, sur terre, sont entièrement dominés par la gravité. Afin de préparer ces expériences, d'autres manipulations sont prévues en laboratoire, en plus d'études théoriques et numériques. En effet, un des buts généraux du projet est d'isoler les phénomènes de base intervenant en ébullition (p.ex. les phénomènes locaux près des lignes de contact, la nucléation, l'influence d'un écoulement, ...), et de les étudier de manière détaillée, afin d'optimiser les codes de simulation destinés à la modélisation du phénomène global et la prédiction des coefficients de transfert d'énergie. [This MAP (Microgravity Application Promotion) research program of the European Space Agency associates several european teams in order to study fundamental and applied aspects of the boiling process. Several microgravity experiments are foreseen, which will allow a deeper understanding of phenomena which, on earth, are generally dominated by buoyancy. In order to prepare these experiments, other investigations are foreseen in the laboratory, in addition to theoretical and numerical studies. Indeed, one of the general goals of the project is to isolate basic phenomena occurring during boiling (i.e. local processes taking place in the vicinity of contact lines, nucleation, forced flows, ...), and to study them in a detailed way, in order to optimize simulation codes dedicated to the modeling of the global process and to the prediction of heat transfer coefficients.]

Déposition organisée de particules induite par l'effet Leidenfrost (FRFC - ODILE) [Organized Deposition Induced by the Leidenfrost Effect (FRFC - ODILE)]
Lorsqu'une gouttelette de liquide est déposée sur une surface plane dont la température excède la température de saturation du liquide, la goutte peut léviter à une distance bien définie de la surface à cause de la vaporisation violente du gaz. Ce phénomène est appelé effet Leidenfrost. Cet état non-mouillant rappelle le comportement d'une gouttelette qui roule sur une feuille de Lotus. Les surfaces naturelles ou artificielles peuvent montrer despropriétés superhydrophobes (surface fakir). Malgré cette analogie, la physique impliquée dans ce dernier cas est très différente de la goutte en Leidenfrost. Le but général du projet ODILE (Organized Deposition Induced by Leidenfrost Effect) est l'étude de gouttes en état Leidenfrost lorsque celles-ci sont composées de fluides complexes tels que des solutions polymères, colloïdales ou encore un mélange de solvant volatil et d'un solide qui cristallise (par exemple un sel). Comme les gouttes s'évaporent pendant leur lévitation, la solution devient de plus en plus concentrée donnant lieu à des transitionsde phase (transition vitreuse pour les polymères, réseau de particules pour les colloïdes, ou encore transition cristalline pour le sel). Ceci conduit à une diminution rapide du taux d'évaporation et mène la goutte à entrer en contact avec le substrat échauffé. La figure de la déposition obtenue après l'évaporation complète sera étudiée théoriquement et expérimentalement, que ce soit sur un substrat plat (déposition auto-organisation) ou sur un substratmicro-structuré (déposition organisée). La vibration verticale du substrat sera également étudiée. [When a liquid droplet is released on a flat surface whose temperature is much higher than the saturation temperature of the liquid, the droplet may 'levitate' at a well-defined distance from the surface due to the violent vaporization of the gas. This phenomenon is called Leidenfrost effect. Such non-wetting state reminds droplets that roll on Lotus leafs. Natural or artificial surfaces may show this superhydrophobic property, so-called 'fakir' effect. The physics involved in the latter case is very different from Leidenfrost effect. In this context, the general goal of the ODILE (Organized Deposition Induced by Leidenfrost Effect) project is to study Leidenfrost droplets made of complex fluids such as polymer solutions, colloidal suspensions or mixtures of a volatile solvent and a crystallizing solute (e.g. a salt). As the droplet evaporates during the levitation, the solute gets more concentrated, generally leading to a phase transition (glassy transition for the polymer, ordered arrays for the colloidal particles, or crystallization for the salt), inducing a rapid decrease of the evaporation rate and leading to contact of the droplets with the heated substrate. The deposition patterns obtained after complete vaporization will be studied theoretically and experimentally, both for flat substrates (self-organized deposition) and for micro-structured plates (shape-organized deposition). Vibrating the surface vertically will also be investigated, as a further way of influencing depositionpatterns via droplet bouncing.]

Microfluidics and micromanipulation: multi-scale applicationsof surface tension (BELSPO PAI Micro-MAST) [Microfluidics and micromanipulation: multi-scale applications of surface tension (BELSPO IAP Micro-MAST)]
The scientific objectives of this IAP network are driven by fundamental questions raised in microfluidics, interfacial science, and micromanipulation. The rational use of surface tension, surface stress and capillary effects in micromanipulation will be applied to a selected number of highly relevant case studies by the network partners, including capillary gripping, capillary filling, capillary alignment, capillary sealing, capillary self-assembly and droplet manipulation (incl. generation and transport). These fundamental questions can be grouped into three categories:1. Fluid statics and dynamics: How much force is applied on solids by menisci and micro-flows in a given geometry? What happens if the solid bends when subject to these forces? Are the interfaces stable and what if not? What is the effect of an electric field? How can the microscopic description of wetting be translated into an adequate boundary condition at the macroscopic level (e.g. contact angle and hysteresis)?2. Surface engineering: How does a contact line move on a rough surface? Can one pattern the surface microscopically to control this motion? How is the motion affected by evaporation, or by the presence of colloid particles in the liquid or at the interface? Do these particles interact with the micro-patterns on the surface? Can one create highly 3D patterns on the surface by using capillary forces (e.g. to bundle nanotubes)?3. Liquid engineering: How to measure the interfacial properties of complex liquids where apart from surface tension a surface viscoelastic response is present? How to infer macroscopic properties from the dynamics at the molecular scale? And how to engineer liquids and tailor them to the requirements arising from applications? Can one make a liquid that is biocompatible, and has a large surface tension and a low viscosity?The proposed multidisciplinary program (involving ULB, ULg, KULeuven, UMons and ESPCI ' Paris) combines forefront research in physics, material science, chemistry and engineering. Its main originality relies in the efforts to enhance the collaboration of the interfacial science, microfluidics and microengineering communities. [The scientific objectives of this IAP network are driven by fundamental questions raised in microfluidics, interfacial science, and micromanipulation. The rational use of surface tension, surface stress and capillary effects in micromanipulation will be applied to a selected number of highly relevant case studies by the network partners, including capillary gripping, capillary filling, capillary alignment, capillary sealing, capillary self-assembly and droplet manipulation (incl. generation and transport). These fundamental questions can be grouped into three categories:1. Fluid statics and dynamics: How much force is applied on solids by menisci and micro-flows in a given geometry? What happens if the solid bends when subject to these forces? Are the interfaces stable and what if not? What is the effect of an electric field? How can the microscopic description of wetting be translated into an adequate boundary condition at the macroscopic level (e.g. contact angle and hysteresis)?2. Surface engineering: How does a contact line move on a rough surface? Can one pattern the surface microscopically to control this motion? How is the motion affected by evaporation, or by the presence of colloid particles in the liquid or at the interface? Do these particles interact with the micro-patterns on the surface? Can one create highly 3D patterns on the surface by using capillary forces (e.g. to bundle nanotubes)?3. Liquid engineering: How to measure the interfacial properties of complex liquids where apart from surface tension a surface viscoelastic response is present? How to infer macroscopic properties from the dynamics at the molecular scale? And how to engineer liquids and tailor them to the requirements arising from applications? Can one make a liquid that is biocompatible, and has a large surface tension and a low viscosity?The proposed multidisciplinary program (involving ULB, ULg, KULeuven, UMons and ESPCI ' Paris) combines forefront research in physics, material science, chemistry and engineering. Its main originality relies in the efforts to enhance the collaboration of the interfacial science, microfluidics and microengineering communities.]



disciplines et mots clés déclarés


Analyse - gestion des transports Environnement et pollution Génie chimique Mécanique appliquée générale Mécanique des fluides Physico-chimie générale Sociologie urbaine Thermodynamique appliquée Transfert de chaleur

absorption caléfaction coalescence coefficient de transfert de chaleur ebullition en film echangeurs de chaleur ecoulement multi-échelle elasto-capillarité electro-capillarité evaporation films minces fluides complexes flux de chaleur critique gouttes instabilités hydrodynamiques interfaces lévitation acoustique ligne de contact lubrification microencapsulation microfluidique micro-fluidique digitale micromanipulation micro-manipulation modélisation théorique et numérique mouillage nanoparticules nucléation surfactants tension superficielle turbulence interfaciale