Evidence of the existence of a transient surface tension between two miscible fluid phases is given. This is done by making use of a density matched free of gravity perturbations, binary liquid of isobutyric acid and water, which presents a miscibility gap and is studied by light scattering. The experiment is performed very near the critical point of the binary liquid, where the diffusion of phases is extremely slow. The surface tension is deduced from the evolution of the structure factor obtained from low angle light scattering. The latter evolution is successfully analyzed in terms of a local equilibrium diffusive approach that makes explicit how the surface tension decreases with time.

A mini splitterless-split-flow thin fractionation (SPLITT) device has been developed to achieve fast separations of micrometer-sized species. In this device, inlet and outlet steps have replaced the splitters, which are common to conventional SPLITT channels. By elimination of the splitters, it becomes straightforward to reduce channel dimensions while maintaining the classic method of fabrication. Reduced dimension channels allow high axial velocity at relatively low flow rate. These high axial velocities generate an enhancement of inertial lift forces and hydrodynamic shear-induced diffusion. Experiments carried out with particulate and biological species in a mini step-SPLITT channel demonstrate that these hydrodynamic effects yield highly enriched fractions of smaller species from binary mixtures.

Split-flow thin channel (SPLITT) fractionation is a technique for continuous separation of particles or macromolecules in a fluid stream into fractions according to the lateral migration induced by application of a field perpendicular to the direction of flow. Typical applications have involved isolation of different fractions from a polydisperse sample. Some specialized applications involve the separation of the fraction influenced by the transverse field from the fraction that is not. For example, immunomagnetically labeled biological cells may be separated from nonlabeled cells with the application of a transverse magnetic field gradient. In such cases, it may be critically important to minimize contamination of the labeled cells with nonlabeled cells while at the same time maximizing the throughput. Such contamination is known as nonspecific crossover (NSC) and refers to the real or apparent migration of nonmobile particles or cells across stream lines with the mobile material. The possible mechanisms for NSC are discussed, and experimental results interpreted in terms of shear-induced diffusion (SID) caused by viscous interactions between particles in a sheared flow. It is concluded that SID may contribute to NSC, but that further experiments and mathematical modeling are necessary to more fully explore the phenomenon.

The response of an air bubble surrounded by a liquid in a sealed cell submitted to vibrations was investigated experimentally under microgravity conditions and compared to experiments under normal gravity conditions. As in normal gravity [1], it was observed that the bubble split into smaller parts when the acceleration of the vibrations reached a threshold. This threshold in microgravity is substantially smaller than that in normal gravity. Experimental results are presented in terms of an acceleration based Bond number which has been found to characterize the bubble behaviour in the laboratory experiments [1].

The behaviour of a vesicle suspension in a simple shear flow between plates (Couette flow) was investigated experimentally in parabolic flight and sounding rocket experiments by Digital Holographic Microscopy. The lift force which pushes deformable vesicles away from walls was quantitatively investigated and is found to be rather well described by a theoretical model by Olla [1]. At longer shearing times, vesicles reach a steady distribution about the center plane of the shear flow chamber, through a balance between the lift force and shear induced diffusion due to hydrodynamic interactions between vesicles. The results obtained in the BIOMICS experiment in the MASER 11 flight are presented and discussed.

We investigate the use of a digital holographic microscope working in partially coherent illumination to study in three dimensions a micrometer-size particle flow. The phenomenon under investigation rapidly varies in such a way that it is necessary to record, for every camera frame, the complete holographic information for further processing. For this purpose, we implement the Fourier-transform method for optical amplitude extraction. The suspension of particles is flowing in a split-flow lateral-transport thin separation cell that is usually used to separate the species by their sizes. Details of the optical implementation are provided. Examples of reconstructed images of different particle sizes are shown, and a particle-velocity measurement technique that is based on the blurred holographic image is exploited.

We report experimental results on the evolution of a laminar liquid jet injected with negatively buoyant condition in a miscible surrounding liquid. Since molecular diffusion is negligible, the only significant miscible effect is the absence of any surface tension. After an initial intrusion phase, the jet reaches a steady-state characterized by a constant penetration depth. A simple theoretical model is derived which successfully predicts the transient phase as well as the subsequent steady state in terms of stationary penetration depth and jet’s profile. All the experimental points collapse on a master curve involving two dimensionless numbers: the densimetric Froude number Fr and S, a number comparing viscous friction to buoyancy. Finally, this curve obtained for laminar flows is compared to classical results on turbulent fountains.

La séparation de particules de taille micronique par la technique dite de SPLITT a mis en évidence des effets de migrations transverses non spécifiques, qui limitent l'efficacité de cette séparation dans le cas d'un mélange de plusieurs espèces. Des expériences en micropesanteur ont montré le rôle important joué par la diffusion hydrodynamique induite par cisaillement dans cette migration anormale. Une nouvelle cellule a donc été mise au point : les particules sont injectées au centre du canal dans l'épaisseur de la cellule et peuvent être focalisées dans n'importe quelle position dans l'épaisseur. La focalisation hydrodynamique ainsi contrôlée permet d'éloigner les particules des parois, où le cisaillement est maximal, afin de minimiser les effets des forces de portance et de diffusion. Les premiers tests de séparation binaire réalisés avec cette cellule de focalisation sont très encourageants puisqu'ils montrent une augmentation notable de l'efficacité, en termes de pureté des échantillons, comparée à celle obtenue avec la cellule de SPLITT.

Interfaces for the 21st Century: New Research Directions in Fluid Mechanics and Materials Science, pp. 279 (2002) No AccessINSTABILITIES AT THE "INTERFACE" BETWEEN MISCIBLE FLUIDS — EMERGENCE OF AN EFFECTIVE SURFACE TENSIONPHILIPPE PETITJEANS, PASCAL KUROWSKI and JUAN FERNANDEZPHILIPPE PETITJEANSLaboratoire de Physique et Mécanique des Milieux Hétérogénes, UMR CNRS 7636, Ecole Supérieure de Physique et de Chimie Industrielles (ESPCI), 10, rue Vauquelin, 75005 Paris, France, PASCAL KUROWSKILaboratoire de Physique et Mécanique des Milieux Hétérogénes, UMR CNRS 7636, Ecole Supérieure de Physique et de Chimie Industrielles (ESPCI), 10, rue Vauquelin, 75005 Paris, France and JUAN FERNANDEZLaboratoire de Physique et Mécanique des Milieux Hétérogénes, UMR CNRS 7636, Ecole Supérieure de Physique et de Chimie Industrielles (ESPCI), 10, rue Vauquelin, 75005 Paris, Francehttps://doi.org/10.1142/9781860949609_0058Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Instabilities can develop at the "interface" between two miscible fluids that exhibit patterns very similar to those observed between immiscible fluids. For example, a layer of colored glycerine hanged-up below a glass plate and placed into a water tank gives rise to organized patterns. Also, a thin layer of glycerine falling into water is unstable and produces falling columns with a regular distance between each other. These similarities between miscible and immiscible fluids lead to the possible existance of an "effective surface tension" between miscible fluids. This effective tension has a meaning for short times only, and should tend to zero with time. It can be explained by the strong concentration gradient at the "interface." FiguresReferencesRelatedDetails Interfaces for the 21st Century: New Research Directions in Fluid Mechanics and Materials ScienceMetrics History PDF download

An experimental study of the transport properties of fluid-saturated joints composed of two complementary rough fracture surfaces, translated with respect to each other and brought in contact, is reported. Quantitative roughness measurements on different fractured granite samples show that the surfaces have a self-affine geometry from which the dependence of the mean aperture on the relative displacement of fracture surfaces kept in contact can be predicted. Variations of the hydraulic and electrical conductances of the joint are measured as functions of its mean aperture. A simple parallel plane model accounts for the global trend of the measurements, but significant deviations are observed when a relative lateral displacement of the surfaces is introduced. A theoretical analysis of their origin shows that they are due both to the randomness of the aperture field and to a nonzero local slope of the surface near the injection hole; the corresponding conductivity fluctuation amplitudes have power law and linear variations with the lateral displacement, and are enhanced by the radial injection geometry.