S. Van Vaerenbergh

Benchmark values for the Soret, thermodiffusion and molecular diffusion coefficients of the ternary mixture tetralin+isobutylbenzene+n-dodecane with 0.8-0.1-0.1 mass fraction

With the aim of providing reliable benchmark values, we have measured the Soret, thermodiffusion and molecular diffusion coefficients for the ternary mixture formed by 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane for a mass fraction of 0.8-0.1-0.1 and at a temperature of 25°C. The experimental techniques used by the six participating laboratories are Optical Digital Interferometry, Taylor Dispersion technique, Open Ended Capillary, Optical Beam Deflection, Thermogravitational technique and Sliding Symmetric Tubes technique in ground conditions and Selectable Optical Diagnostic Instrument (SODI) in microgravity conditions. The measurements obtained in the SODI installation have been analyzed independently by four laboratories. Benchmark values are proposed for the thermodiffusion and Soret coefficients and for the eigenvalues of the diffusion matrix in ground conditions, and for Soret coefficients in microgravity conditions.Graphical abstract

Technical Note Marangoni instability of a layer of binary liquid in the presence of nonlinear Soret effect

Abstract Although the Soret effect induces only small chemical separations, its influence on the variations of physical parameters may be larger than the influence of the thermal gradient from which it results. The effect has been recognized and extensively studied in the Rayleigh–Benard problem for instabilities generated by density fluctuations 1 , 2 , 3 , 4 . In the same way that for the mixture density, the Soret effect may influence significantly the surface tension variations in the presence of a temperature gradient. The interaction between thermocapillary and concentration-capillary mechanisms for promoting motion in binary mixture fluids has motivated many authors to study the Marangoni–Benard instability in the presence of the Soret effect and important similarities with the Rayleigh–Benard convection have been evidenced [5] .

On the problem of natural convection in liquid phase thermotransport coefficients measurements

We focus in this paper on the effect of natural convection in thermodiffusion coefficients measurements in liquid metal alloys both for normal and microgravity conditions. Our previous experimental results are briefly recalled, with a special emphasis on the data recently obtained from the EURECA space mission. With respect to the ground based values, it is seen that the solutal separation is always significantly higher in microgravity, even in systems where solutal stabilization of the flow has an effect. Simple scaling analysis arguments show that the error induced by additional convective transport scales with the square of the fluid velocity. Such a result compares favorably with existing three dimensional (3D) numerical data. The theory also accounts qualitatively for the reduced separation observed experimentally in ground based set-ups. We conclude that it is in principle possible to perform accurate measurements in space, but that the size of the capillaries used in the experiments should always b...

Modification of morphological stability by Soret diffusion

Abstract The solute mass transport that may lead to morphological instabilities in directional solidification is described within the framework of the nonlinear thermodynamics of irreversible processes. Specific calculations are carried out for tin-bismuth alloys for two models of the concentration dependence of the thermodiffusion flux. Depending on the sign of the thermodiffusion coefficient, morphological stability may be increased or decreased.

Influence of thermal boundary conditions on the double-diffusive process in a binary mixture

This paper presents a precise numerical simulation of the transport processes in a rectangular cavity saturated with a binary liquid mixture. The full transient Navier-Stokes equations coupled with the mass and heat transfer equations are solved, numerically, using the finite-volume method. After validation against a proven commercial code comparing solutions on a benchmark natural convection problem, the newly developed code is used for a series of numerical experiments. Realistic thermal boundary conditions have been chosen, and the more drastic situation of power loss while conducting the experiment in microgravity is considered. The molecular and thermal diffusion coefficients are computed from theoretical models. Results reveal that, when vertical walls are held at constant but different temperatures, species separate in both the longitudinal and the transverse directions as radiation is allowed to take place along the horizontal walls. The numerical experiments performed clearly demonstrate that the kinetics of the mass transport in the mixture are conditioned by the ability to monitor the heat sources properly. Specifically, sudden temperature changes strongly disturb species separation in the experimental cells. This paper provides some trends for the accurate analysis of experiments involving mass transport inasmuch as the convective level is low enough to allow evaluation of the transport coefficients.

Multicomponent transport studies of crude oils and asphaltenes in DSC program

Crude oils have matured during ages in reservoirs under obvious non-equilibrium conditions. The resulting stratification and phases present can be predicted only with non-equilibrium thermodynamics tools. Possibly, convection is present and enforced by the Soret effect. These parameters are the focus of the MAP DSC (Diffusion and Soret Coefficients) multicomponent studies. Theoretical and ground based studies are completed by measurements performed in the SCCO experiments (Soret Coefficients of Crude Oils), of the DSC experiment on SODI facility (Beginning 2008). The problem is presented here in a simplified manner using Maxwell-Stéfan formalism, and is applied to some situations occurring in reservoirs and in the GATE experiment proposed for the study of growth conditions of asphaltenes.

The role of the Soret effect on Marangoni-Benard stability

The role of the Soret effect in the Marangoni-Benard stability of binary mixtures is analyzed by the local potential technique. The transients of the thermotransport process are considered. This analysis shows how the temperature difference across the layer leading to convection is a function of the time needed to trigger convection and how oscillatory convection domain extends with this time.

Oscillations induced by purely diffusive processes in planar directional solidification from the melt

The planar growth of directional solidification from a binary melt is analyzed taking into account thermodiffusive transport. Both stable and overstable planar growth regimes are considered in the case of dilute alloys and as far as convective process does not modify the extent of the solute transition zone (the diffusion boundary layer) that appears in the absence of convection. Under such conditions, thermodiffusion appears as a thermophoretic transport process. The extent of the diffusion boundary layer is divided by a factor μc = 1 + DTGlV, where DT is the thermodiffusion coefficient, Gl the interface thermal gradient in the melt and V the growth rate. The solute profile is modified accordingly. Planar overstable modes under the form of striations, are predicted. They appear with a period of the order of the ratio of the isothermal diffusion coefficient divided by the square of the growth rate. Such instabilities are expected in constitutionally supercooled melts for systems with large positive liquidus slopes and Soret coefficient for a threshold value of the solute concentration.

Numerical Study of Solutal and Thermal Instabilities in Mini-Channels for Membrane-Less Applications

Many industrial processes make extensive use of membranes to separate fluxes while allowing some of the constituent species to diffuse into each other. In recent years, high production and maintenance costs induced by fouling, poisoning and clogging of the membrane pores due to impurities have create conditions to study alternative way of making liquid and/or gaseous streams interact and diffuse without the presence of a physical barrier. One of the possibilities is offered by the essentially laminar character of the flow in microfluidic devices that allows two or more different fluid streams to merge without mixing in a large range of experimental and industrial conditions. In this work, we will study, numerically, the case of two streams of different composition merging in a micro-channel. The upper and lower sides of the micro-channel are heated differentially and the inlet velocity of the streams is set independently in the range 0–1m/s. Simulations are carried out in 2D and 3D while fluids are chosen by considering their industrial importance and application. The main results are that the stability of the streams is very sensitive to the inlet conditions and that it is possible to modulate the mixing layer thickness by acting on thermal gradients, geometrical constraints and slip flow conditions.Copyright