Dynamics of three-dimensional wavy liquid films
Collaborations : B. Scheid (ULB, Brussels), W. Rohlfs and Reinhold Kneer (RWTH Aachen)
Three-dimensional waves developing on the
free surface of falling liquid films intensify convective transport
in the adjacent phases, which influences the efficiency of multiphase
processes such as distillation. Here, we study the effect of these
surface waves on the velocity field and vice-versa by way of full
numerical simulations (VOF-CSF method).
G. F. Dietze, W. Rohlfs, K. Nährich, R. Kneer and B. Scheid J. Fluid Mech. 743, 75 (2014)
Thin film deposit in a dip-coating-like process
In coating achieved by solvent evaporation from a polymer solution or a colloidal dispersion, complex phenomena occur in the vicinity
of the contact line where the evaporation flux is maximum.
Hydrodynamics and evaporation may induce self patterning, as illustrated in the image (left) for a silica colloidal suspension (deposit height
∼ 1 µm; wavelength ∼ 100µm).
F. Doumenc et al. Langmuir 32, (2016)
doi: 10.1021/acs.langmuir.6b02282
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Evaporation close to a contact line: modeling and numerical simulation
Evaporation close to a contact line or a meniscus is encountered in many processes (bubble nucleation, coating, heat-pipes etc.) We are developing models and numerical tools to describe hydrodynamics and heat and mass transfer in such processes, taking into account the different scales involved in the flow. The figure (left) shows the stream lines induced by evaporation and substrate motion for a complete wetting configuration.
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Climatology and vermiculation in caves
Humidity in caves is most often very high and small temperature changes may induce locally evaporation or condensation on the walls. A current phenomenon observed on these cave walls is the formation of small clusters of heterogeneous materials (clay materials, pigments, calcite, organic material...) that were initially on the wall. The figure to the side is an illustration of this natural process, called vermiculation, which is still not understood. It becomes troublesome when it affects wall paintings. To investigate the vermiculation process, we analyze the interplay between climatology, thin aqueous film formation and clay material cohesion.
Falling liquid film in interaction with a gas
Heat and/or mass transfer between a liquid and gaseous phase can be realized with the help of falling liquid films. These flows are unstable
with respect to interfacial disturbances and, as a result, develop surface waves, which intensify the underlying transfer mechanisms.
The image on the left shows streamlines within a liquid film and its surrounding gaseous atmosphere (top: counter-current, fixed reference frame; bottom: co-current, moving reference frame).
These representations evince the occurrence of several wave-induced vortices.
G. F. Dietze, C. Ruyer-Quil J. Fluid Mech. 722, 348 (2013)
Rayleigh-Bénard-Marangoni convection induced by solvent evaporation in a plane layer
When drying a polymer solution, solvent evaporation induces a decrease of the temperature and the solvent concentration at the surface so that
the configuration may become unstable (thermal or solutal Rayleigh-Bénard-Marangoni instability). Theoretical analysis and numerical simulations have been performed to investigate
the respective influence of the different mechanisms on convection onset. The figure shows the evolution of the viscosity field during drying.
S.G. Yiortsios, S.K. Serpetsi, F.Doumenc, B.Guerrier IJHMT 89, (2015)
doi: 10.1016/j.ijheatmasstransfer.2015.06.015
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Instabilités 3D d'un film tombant
Un film liquide tombant sur un plan incliné se déstabilise pour former une onde solitaire composée d'une onde principale précédée de petites ondes capillaires. Ces ondes capillaires se déstabilisent à leur tour pour générer des motifs tridimensionnels. Les conditions d'apparition de ces instabilités 3D sont étudiées expérimentalement grâce à des cartes d'épaisseur de film obtenues par une méthode optique de type Schlieren.
J. of Fluid Mechanics, 757, (2014), doi: 10.1017/jfm.2014.506
Cisaillement d'un film tombant par un contre-écoulement d'air
La dynamique des ondes se développant à la surface d'un film liquide tombant est modifiée lorsqu'un contre-écoulement de gaz est imposé à l'interface. Nous analysons expérimentalement le comportement du film soumis à des vitesses de gaz croissante. Nous recherchons les conditions pour lesquelles le train d'ondes rebrousse chemin avant d'être détruit, situation désignée comme étant l'engorgement de notre système. La photo ci-contre illustre un cas pour lequel l'écoulement de gaz génère des structures 3D localisées de grande amplitude et rapides empêchant l'apparition de l'engorgement.
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