Benchmark values for the Soret,thermal diffusion and diffusion coefficients of three binary organic liquid mixtures

With the aim of providing reliable benchmark values, we have measured the Soret, diffusion and thermal diffusion coefficients of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4 tetrahydronaphthalene for a concentration of 50 wt% at a temperature of 25C. The experimental techniques applied by the five participating laboratories are transient holographic gratings, annular and parallelepipedic thermogravitational columns, and vertical parallelepipedic columns with velocity amplitude determination by laser doppler velocimetry. The systems have also been studied in a annular thermogravitational column filled with a porous medium in the gap. There is a good agreement between the different experiments with deviations of the order of a few per cent in most cases (8.5% at most). The numerical values are tabulated in the paper.     

Transient-state method for coupled evaluation of Soret and Fick coefficients,and related tortuosity factors,using free and porous packed thermodiffusion cells: Application to CuSO4 aqueous solution ( 0.25M)

The measurement of Soret coefficients in liquids is not easy and usually not very precise because the resulting concentration gradient is small and moreover can be perturbed by undesired convection currents. In order to suppress, or to drastically reduce these convection currents, the use of a porous medium is sometimes suggested. The question arises as to whether the Soret coefficient is the same in free fluid and in porous medium. This is the aim of this paper. To this end, for a given liquid mixture, the time evolution of the vertical concentration gradient is experimentally measured in the same thermodiffusion cell filled first with the free liquid and next with a porous medium followed by saturation by the liquid mixture. Both the isothermal diffusion (Fick) coefficient and the Soret coefficient can be deduced, providing that a correct working equation is used. The proposed equation results from integration of the general mass conservation equation with realistic boundary conditions (zero mass flux at the boundaries) and some simplifying assumptions rendering this equation more tractable than the one proposed some decades ago by Bierlein (J.A. Bierlein, J. Chem. Phys. 23, 10 (1955)). The method is applied here to an electrolytic solution (CuSO4, 0.25 M) at a mean temperature of 37^°C. The Soret coefficients in free and porous medium (zircon microspheres in the range of 250- 315 ^. 10^-6m) may be considered to be equal ( S_T = 13.2±0.5 ^. 10^-3 K^-1) and the tortuosity factors for the packed medium are the same relative to thermodiffusion and Fick coefficients ( = 1.51±0.02).     

Thermal convection around obstacles: the case of Sierpinski carpets

Measurements of free convection velocity profiles by laser Doppler velocimetry in a cavity containing Plexiglas reconstructed Sierpinski carpets are compared with computed profiles using the SIMPLER numerical code applied to the Navier–Stokes equations. This first step validates the numerical code into which two thermal conductivities are used (that of the liquid and that of the solid), together with two viscosities (that of the liquid and a fictitious high viscosity of the order of 10³⁰ for the solid). Next, the code is used for a network of Sierpinski carpets, allowing the evaluation of a seepage velocity from the Navier–Stokes equations.     

Thermal convection in superposed immiscible liquid layers

This paper deals with thermal convection in two superposed immiscible fluid layers in a rectangular cavity with differentially heated end walls. We have measured the horizontal velocity profiles in each layer as a function of elevation and we show the dominant rôle of interfacial tension effects. Experiments were conducted using Laser Doppler Anemometry; the system studied was water-heptanol.

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Résumé Cet article concerne la convection thermique dans deux couches fluides non miscibles, superposées et contenues dans une cavité rectangulaire dont les parois latérales sont maintenues à des températures différentes. Nous mesurons le profil horizontal de vitesse dans chaque couche, en fonction de la hauteur et nous montrons le rôle dominant des effects de tension interfaciale. Les résultats expérimentaux sont obtenus par anémométrie Laser Doppler sur le système eau-heptanol.

     

Soret coefficients in some water-methanol, water-ethanol, and water-isopropanol systems

In this article, we re-examine the published experimental values of the Soret coefficients of a few water-alcohol systems at a mean temperature of 37.5 degrees C, because we feel that these published values (including microgravity values) are doubtful. The main technique applied is the use of thermogravitational columns to determine the thermodiffusion coefficient. The obtained values did not agree with the published values; worse, sometimes the sign was different.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Untypical Surface Properties of the System Caprylic Acid + n-Propyl Acetate

The surface tensions of nonaqueous solutions of n-propyl acetate in caprylic (n-octanoic) acid were measured between 273 and 303 K using the Wilhelmy plate method. Complicated concentration dependences were obtained, different from any previously reported. In addition, independent volumetric and acoustic (sound velocity and absorption) methods were applied. The results are interpreted in terms of formation of weak complexes in the bulk as well as at the surface.     

Influence of interfacial tension gradients on thermal convection in two superposed immiscible liquid layers

This paper considers mainly the theoretical aspect of thermal convection in two superposed immiscible (or partially miscible) fluid layers in a rectangular cavity with differentially heated end walls. We develop a model valid for layers whose lateral extent is much larger than depth, deriving the horizontal velocity profile in each layer as a function of the various parameters such as expansion coefficients, viscosities, depth of each layer, and the interfacial tension gradient along the interface. Results are discussed, taking into account the results of experiments that we presented recently [1].

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Résumé Cet article étudie les aspects théoriques de la convection thermique dans deux couches fluides non miscibles (ou partiellement miscibles), superposées et contenues dans une cavité rectangulaire dont les parois latérales sont maintenues à des températures différentes. Nous développons un modèle valide pour des couches dont les dimensions latérales sont beaucoup plus grandes que leur épaisseur et déduisons le profil horizontal de vitesse dans chaque couche, en fonction des nombreux paramètres du problème, à savoir les coefficients de dilatation, les viscosités et les épaisseurs des deux couches, et le gradient de tension interfaciale le long de l'interface. Les résultats sont discutés en prenant en considération les expériences existantes que nous avons présentées récemment [1].

     

Laminar thermal convection in a vertical slot

The validity of the conduction regime approximation is studied in a vertical slot of height to width aspect ratio equal to 28. Velocity profiles are determined by laser-Doppler velocimetry (LDV) in water and hexane near room temperature, but also in water at mean temperatures close to its density maximum. Finally a glycerol-water mixture is experimentally studied in order to check the theoretical prediction taking into account the temperature dependence of the viscosity (non-Boussinesq effects). The measured velocity profiles and the computed ones, both analytically for an infinite layer or by 2D numerical simulations, are in excellent agreement for all Grashof numbers. When the density is a quadratic function of temperature, a criterion is derived for the existence of a bicellular convective regime. The validity of this criterion is also experimentally verified. Finally, for a highly viscous fluid, the conduction regime approximation is found to be valid for an aspect ratio greater than 4.     

Measurements of thermally-induced convection in a model porous medium

The velocity field generated by thermal convection in a model porous medium is experimentally determined by means of both PIV and LDA techniques. Details of matching refraction index under non isothermal conditions are given. Fields are measured in the empty parallelepipedic cell and in a model medium made of parallel circular bundles. Results are in good agreement. Moreover, by an averaging technique, we are able to measure seeping velocity profiles.