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Mutual diffusion of six hydrocarbons (methane, ethane, isobutane, benzene, toluene or naphthalene) diluted in supercritical carbon dioxide (CO 2) is studied by molecular dynamics simulation near the Widom line, i.e. in the temperature range from 290 to 345 K along the isobar 9 MPa. The CO 2 + aromatics mixtures are additionally sampled at 10 and 12 MPa and an experimental database with Fick diffusion coefficient data for those systems is provided. Taylor dispersion experiments of CO 2 with benzene, toluene, n-dodecane and 1,2,3,4-tetrahydronaphthalene are conducted along the p= 10 MPa isobar. Maxwell–Stefan and Fick diffusion coefficients are analyzed, together with the thermodynamic factor that relates them. It is found that the peculiar behavior of the Fick diffusion coefficient of some CO 2 mixtures in the extended critical region is a consequence of the thermodynamic factor minimum due to pronounced clustering on the molecular scale. Further, the strong dependence of the Fick diffusion coefficient on the molecular mass of the solute as well as the breakdown of the Stokes–Einstein relation near the Widom line are confirmed. Eleven correlations for the prediction of the Fick diffusion coefficient of CO 2 mixtures are assessed. An alternative two-step approach for the prediction of the infinite dilution Fick diffusion coefficient of supercritical CO 2 mixtures is proposed. It requires only the state point in terms of temperature and pressure (or density) as well as the molecular solute mass as input parameters. First, entropy scaling is applied to estimate the self-diffusion coefficient of CO 2 .Subsequently, this coefficient is used to determine the infinite dilution Fick diffusion coefficient of the mixture, based on the finding that these two diffusion coefficients exhibit a linear relationship, where the slope depends only on the molecular solute mass., SCOPUS: ar.j, info:eu-repo/semantics/published

The effect of traces of ethanol in supercritical carbon dioxide on the mixture's thermodynamic properties is studied by molecular simulations and Taylor dispersion measurements. This mixture is investigated along the isobarp= 10 MPa in the temperature range betweenT= 304 and 343 K. Along this path, the mixture undergoes two transitions: First, the Widom line is crossed, marking the transition from liquid-like to gas-like conditions. A second transition occurs from the supercritical gas-like domain to a subcritical gas. The Widom line crossover entails inflection points for most of the studied properties,i.e.density, enthalpy, shear viscosity, Maxwell-Stefan and intradiffusion coefficients. On the other hand, the transition between the super- and subcritical regions is found to be generally smooth, an observation that is qualitatively confirmed by experimental Taylor dispersion measurements. Dedicated atomistic simulations show the presence of microheterogeneities due to ethanol self-association along the investigated path, which lead to the mixture's anomalous behavior in its extended critical region., SCOPUS: ar.j, info:eu-repo/semantics/published

In the presence of temperature gradients along the gas-liquid interface, a liquid bridge is prone to hydrothermal instabilities. In the case of a coaxial gas stream, in addition to buoyancy and thermocapillary forces, the shear stresses and interfacial heat transfer affect the development of these instabilities. By combining experimental data with three-dimensional numerical simulations, we examine the evolution of hydrothermal waves in a liquid bridge with with a gas flow parallel to the interface. The gas moves from the cold to the hot side with a constant velocity of and its temperature is the main control parameter of the study. When the thermal stress exceeds a critical value, a three-dimensional oscillatory flow occurs in the system. A stability window of steady flow has been found to exist in the map of dynamical states in terms of gas temperature and applied thermal stress. The study is carried out by tracking the evolution of hydrothermal waves with increasing gas temperature along three distinct paths with constant values of: Path 1 is selected to be just above the threshold of instability while path 2 traverses the stability window and path 3 lies above it. We observe a variety of dynamics including standing and travelling waves, determine their dominant and secondary azimuthal wavenumbers, and suggest the mathematical equations describing hydrothermal waves. Multimodal standing waves, coexistence of travelling waves with several wavenumbers rotating in the same or opposite directions are among the most intriguing observations., SCOPUS: ar.j, SCOPUS: ar.j, info:eu-repo/semantics/published

The stability of convective flows in a non-homogeneous temperature field is affected by the shape of the container hosting the fluid. We present a nonlinear two-phase computational study of convection in a liquid bridge that develops under the action of buoyancy and Marangoni forces. The hydrothermal instability is examined for three shapes of disks supporting liquid bridge: both disks flat, the upper (hot) disk tapered, and the lower (cold) disk tapered. Steady flow is also analyzed for the case that both disks are tapered. In all the cases of instability, the flow pattern comprises, but is not limited to, a hydrothermal wave with an azimuthal wavenumber m = 2. An intriguing flow pattern is observed in the case of flat disks when the nonlinear interaction between the modes m = 0 and m = 2 leads to quasiperiodic motion forming a torus in the phase space. The torus originates from two traveling waves (TW) with the same mode m = 2 but with distinct (close) frequencies. Note that this was not observed in the one-phase model. The case with a tapered cold disk reveals an oscillatory state with a single TW wave associated with m = 2 mode. In the case of a tapered hot disk, an axially symmetric TW with m = 0 is observed first and, at later times, is accompanied by a TW with m = 2., SCOPUS: ar.j, info:eu-repo/semantics/published

Thermodiffusion, which leads to a component separation in a mixture due to the thermal gradient, still does not have an unambiguous microscopic picture. Therefore, experimental studies, especially in convection free environment, are important. As part of the 4th campaign on the DCMIX project, thermodiffusion experiments on three compositions of the toluene-methanol-cyclohexane ternary mixture, on a mixture of fullerene-tetralin-toluene and on a mixture of polystyrene-toluene-cyclohexane have been performed in microgravity conditions on board the International Space Station. A binary mixture of polystyrene-toluene has been filled into the companion cell for the campaign. The Selectable Optical Diagnostics Instrument (SODI), wich is a two-wavelength Mach-Zehnder interferometer for the ternary mixtures, plus a monochromatic Mach-Zehnder interferometer for the binary mixture, has been used in order to obtain the temperature and the concentration fields in the cells. Precisely, it is a 5-steps phase-shifting interferometry technique which is implemented with SODI, producing by means of laser illumination a set of 5 phase-shifted images of π/2 between them as function of the time. A total of 58 runs of various durations and at different mean temperatures have been conducted. Here, we evaluate the contrast of the interferograms, the quality in the phase stepping, the stability of the thermal regulation of the experiments and the level of environmental disturbances on board the space station during the campaign., SCOPUS: ar.j, info:eu-repo/semantics/published

This study aims at contributing to quinine extraction using supercritical CO2 and ethanol as a co-solvent. The diffusion coefficients of quinine in supercritical CO2 are measured using the Taylor dispersion technique when quinine is pre-dissolved in ethanol. First, the diffusion coefficients of pure ethanol in the supercritical state of CO2 were investigated in order to get a basis for seeing a relative change in the diffusion coefficient with the addition of quinine. We report measurements of the diffusion coefficients of ethanol in scCO2 in the temperature range from 304.3 to 343 K and pressures of 9.5, 10 and 12 MPa. Next, the diffusion coefficients of different amounts of quinine dissolved in ethanol and injected into supercritical CO2 were measured in the same range of temperatures at p = 12 Mpa. At the pressure p = 9.5 MPa, which is close to the critical pressure, the diffusion coefficients were measured at the temperature, T = 343 K, far from the critical value. It was found that the diffusion coefficients are significantly dependent on the amount of quinine in a small range of its content, less than 0.1%. It is quite likely that this behavior is associated with a change in the spatial structure, that is, the formation of clusters or compounds, and a subsequent increase in the molecular weight of the diffusive substance.

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Experiments aboard the International Space Station (ISS) provide a large but still limited amount of data. A complete set of data is usually returned to Earth on a flash disk a few months later, by which time the experimental facility has already been put into storage or trashed. Thus, scientists have no possibility to repeat the experiment, even if some ambiguities are later found. Therefore, onboard experiments require careful preparation on the ground with multiple tests in the laboratory and in parabolic flights, if possible. Furthermore, during postflight analysis, it is important to clarify all unknown sources of errors. One of the most obvious sources of perturbations on the ISS is g-jitter. Here, we present the preparation and implementation of the Influence of Vibrations on Diffusion in Liquids (IVIDIL) experiment on the ISS, which studied the effect of random g-jitter and given vibrations on diffusion-controlled experiments in liquid mixtures. Since diffusion in liquids is a slow process, only vibrational effects were examined in parabolic flights. A methodology for the analysis of diffusion and thermodiffusion processes was developed in the laboratory., info:eu-repo/semantics/published

When a container with two distinct fluids is subjected to vibrations in microgravity, the interface may undergo a variety of instabilities and develop towards a complex structure, as seen in recent parabolic flight experiments using both miscible and immiscible liquids. Among other things, the selected pattern depends on the frequency and amplitude of the forcing and, crucially, on its orientation with respect to the initial interface. In a parabolic flight experiment, this initial orientation is largely determined by the stage of the parabolic manoeuvre when the forcing is started and the residual gravity level during the period of microgravity. It plays a key role in the appearance of defects and irregularities during the evolution of the interface triggered by the frozen wave instability. Using numerical simulations, we systematically investigate the effect of initial interface orientation on pattern selection in microgravity for both miscible and immiscible fluids, and compare to available experiments. When the interface and the forcing are nearly aligned, the frozen wave instability is dominant, leading to the development of approximately regular columnar patterns. As the initial angle becomes more oblique, the frozen wave growth becomes more irregular and asymmetric and may involve thin auxiliary columns. Sufficiently large angles suppress the frozen wave instability and, depending on the container aspect ratio, may result in a simple two-column final state., info:eu-repo/semantics/published

A detailed numerical investigation of frozen wave pattern selection in finite rectangular containers under microgravity conditions is presented. The column growth cycle controlling mode transitions is described and the instability diagram showing selected wave number as function of the vibrational velocity is obtained. In contrast to the continuous monotonic dependence of pattern wave number on forcing predicted by linear inviscid theory in the limit of infinitely long containers, the pattern selection process in finite domains is characterized by solution branches that persist over discrete forcing intervals. We describe how properties of the selected frozen wave pattern, including the finite critical forcing value, depend on container length. In long containers, a transition from nearly symmetric to asymmetric columnar development is found at sufficiently high forcing values, with the loss of (approximate) reflection symmetry evident in the mean flow associated with the transient growth of the pattern. The effect of container height is considered separately, in the limit of both shallow and deep layers. Shallow layers suppress the development of long-wave perturbations leading to higher wave-number patterns whose growth may be associated with an asymmetric series of collisions between developing columns and container boundaries. In thick layers, lower pattern wave numbers are observed and, although the column growth is on average more regular, the final state is often asymmetric. Finally, we compare our results with the dependence on container aspect ratio Γ=L/2H predicted by inviscid theory. For Γ2, finite-size effects are reasonably weak and the numerically obtained thresholds are similar to but slightly higher than the theoretical values, most likely due to viscous effects. For Γ2, finite-size effects come to the fore and onset is significantly delayed., SCOPUS: ar.j, info:eu-repo/semantics/published

This paper is addressing the challenge related to understanding the experimental results obtained by Taylor dispersion technique when working under high pressure with supercritical carbon dioxide (CO2). We discuss typical experimental problems that arise when using the Taylor dispersion method for measuring diffusion coefficients in the supercritical fluids. The diffusion coefficients of the two samples in supercritical carbon dioxide were measured along the isobars at different temperatures. The diffusion coefficients of ethanol in supercritical CO2 have been measured in the temperature range from 304.15 to 343 K along the isobar p = 12.0 MPa. Experiments with the gaseous CH4/CO2 mixture with a mole fraction of CH4 = 0.2052 mol mol− 1 have been conducted in the temperature range from 317.85K to 343.15 K along the isobar p = 12.5 MPa. A comparative analysis of a diffusion behavior of these very different mixtures is presented., SCOPUS: ar.j, info:eu-repo/semantics/published

In the frame of the Diffusion Coefficient Measurements in ternary mIXtures 4 (DCMIX4) project the thermodiffusion experiments were conducted on the International Space Station (ISS) in the Selectable Optical Diagnostics Instrument (SODI) which is on orbit since 2009. We describe the results of the preliminary analysis of images downloaded during the execution of DCMIX4 in order to check the quality of the running experiments and, if needed, adjust the experiment parameters for the following runs. The quick analysis of raw data showed that they are meaningful and will allow to obtain the transport coefficients of examined ternary and binary mixtures. Graphical abstract: [Figure not available: see fulltext.]., SCOPUS: ar.j, info:eu-repo/semantics/published

This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed. Graphical abstract: [Figure not available: see fulltext.]., 0, SCOPUS: re.j, SCOPUS: re.j, info:eu-repo/semantics/published

We consider the response to periodic forcing between 5 Hz and 50 Hz of an interface separating immiscible fluids under the microgravity conditions of a parabolic flight. Two pairs of liquids with viscosity ratios differing by one order of magnitude are investigated. By combining experimental data with numerical simulations, we describe a variety of dynamics including harmonic and subharmonic (Faraday) waves, frozen waves and drop ejection, determining their thresholds and scaling properties when possible. Interaction between these various modes is facilitated in microgravity by the relative ease with which the interface can move, altering its orientation with respect to the forcing axis. The effects of key factors controlling pattern selection are analysed, including vibrational forcing, viscosity ratio, finite-size effects and residual gravity. Complex behaviour often arises with features on several spatial scales, such as Faraday waves excited on the interface of a larger columnar structure that develops due to the frozen wave instability - this type of state was previously seen in miscible fluid experiments but is described for the first time here in the immiscible case., SCOPUS: ar.j, info:eu-repo/semantics/published

We present an experimental and complementary computational study of a two-phase flow in a liquid bridge that develops under the action of buoyant and Marangoni forces in the presence of a gas stream parallel to the interface. The gas flow is counter-directed with respect to the steady flow in liquid. The forced gas flow along the interface provides actions on the system via shear stresses and heat exchange. For the experimental fluids (n-decane, nitrogen) the ratio of viscosities is large, about 40, and the gas Reynolds number is moderate, Reg = 120. Thus, heat transfer is the prevailing mechanism by which gas affects the flow in a liquid. The effect of gas temperature on the evolution of flow states is examined. The study reveals that in the supercritical region, ΔT>1.25ΔTcr, the flow dynamics can be divided in three regimes relative to the gas temperature. When the gas is colder than the temperature of the supporting disk, multiple transitions between the oscillatory states occur: periodic, quasi-periodic with two frequencies, quasi-periodic with three frequencies and noisy quasi-periodic with three frequencies. In the case, when the gas temperature approaches the temperature of the cold disk and goes up to the mean temperature, the flow remains periodic up to the largest tested ΔT. In the case of hotter gas, the flow also remains periodic far above the threshold of hydrothermal instability, but the azimuthal mode of the periodic oscillatory flow is changed. The stability window is found to exist between these two azimuthal modes and its location is sensitive to the gas parameters as well as to the geometry of a liquid bridge. It opens a possibility that oscillatory instability can be stabilized by choosing specific temperatures and velocities of counter-current gas., SCOPUS: ar.j, info:eu-repo/semantics/published

We develop a connection between instabilities in a two-liquid miscible system and in a liquid mixture with a linear distribution of density. In both cases, the liquids are placed in a closed cell and subjected to horizontal oscillations at different frequencies and amplitudes in a microgravity environment. The study includes parabolic flight experiments and numerical simulations. We examine the transformation of the interfacial pattern when the diffusive interface widens from a thin transient zone occupying 4% of the cell height to a situation when it occupies the entire cell height. In the case of sharp concentration (density) difference between miscible liquids, under reduced gravity conditions, instability leads to the formation of rectangular columns of liquids of alternating densities with an amplitude nearly equal to the height of the cell. The increase of the interface width promotes the selection of a smaller wave number associated with columns. The experimental observations are confirmed by the numerical simulations. In order to quantify the pattern regimes, we suggested to use the averaged mass flux through the mid-height of the cell., SCOPUS: ar.j, info:eu-repo/semantics/published

With laboratory and numerical work, we demonstrate that one of the main diffusion coefficients and the smaller eigenvalue of the Fick diffusion matrix are invariant to the number of methylene groups of the alcohol in ternary mixtures composed of an aromatic (benzene), a ketone (acetone) and one of three different alcohols (methanol, ethanol or 2-propanol). A critical analysis of the relationship between the kinetic and thermodynamic contributions to the diffusion coefficients allows us to explain this intriguing behaviour of this class of mixture. These findings are reflected by the diffusive behaviour of the according binary subsystems. Our approach provides a promising systematic framework for future investigations into the important and challenging problem of transport diffusion in multicomponent liquids., SCOPUS: ar.j, info:eu-repo/semantics/published

In spite of considerable research on the nature of aqueous alcohol mixtures that are characterized by microscopic inhomogeneity or incomplete mixing at the molecular level, transport properties have received little attention. We report the results of a study on diffusion in the ternary mixture of water with two alcohols, that is, water + methanol + ethanol, which is investigated on microscopic and macroscopic scales by means of molecular simulation and Taylor dispersion experiments. A novel protocol is developed for the comparison of mutual diffusion coefficients sampled by two fundamentally different approaches, which allows for their critical analysis. Because of complex intermolecular interactions, given by the presence of hydrogen bonding, the analysis of transport processes in this mixture is challenging for not only on the microscopic scale for simulation techniques but also on the macroscopic scale due to unfavorable optical properties. Binary limits of the Fick diffusion matrix are used for validation of the experimental ternary mixture results together with the verification of the validity of the phenomenological Onsager reciprocal relations. The Maxwell-Stefan diffusion coefficients and the thermodynamic factor are sampled by molecular simulation consistently on the basis of given force field models. The protocol for the comparison of the results from both approaches is also challenging because Fick diffusion coefficients of ternary mixtures depend on the frame of reference. Accordingly, the measured coefficients are transformed from the volume-averaged to the molar-averaged frame of reference, and it is demonstrated that both approaches provide not only similar qualitative behavior along two concentration paths but also strong quantitative agreement. This coordinated work using different approaches to study diffusion in multicomponent mixtures is expected to be a significant step forward for the accurate assessment of cross-diffusion. (Figure Presented)., SCOPUS: ar.j, info:eu-repo/semantics/published

We have discovered a peculiar behaviour of the interface between two miscible liquids placed in a finite-size container under horizontal vibration. We provide evidence that periodic wave patterns created by the Kelvin-Helmholtz instability and Faraday waves simultaneously exist in the same system of miscible liquids. We show experimentally in reduced and normal gravity that large-scale frozen waves yield Faraday waves with a smaller wavelength on a diffusive interface. The emergence of the different scale patterns observed in the experiments is confirmed numerically and explained theoretically., SCOPUS: ar.j, info:eu-repo/semantics/published

We examine the dynamics of a binary mixture in a cubic cell subjected to a temperature differential and oscillatory forcing. The Soret effect, which is negative in the present study, provides a coupling mechanism by which a temperature gradient establishes a concentration gradient in a mixture. We present the results of experiments that were performed on the International Space Station (ISS) and compare the observations with the results of direct numerical simulations. The evolution of temperature and concentration fields is investigated by optical digital interferometry. One advantage of the experimental technique is the observation of the fields along two perpendicular directions of the cell, allowing us to restore the three-dimensional field. Experimental evidence disproves speculations that the ISS microgravity environment always affects diffusion-controlled processes. Furthermore, we demonstrate that imposed vibrations with constant frequency and amplitude create slow mean flows and that they do influence the diffusion kinetics. The perturbation of the diffusive fields scales as the square of the vibrational velocity. In addition to calculations of the full three-dimensional Navier-Stokes equations, a two-time-scale computational methodology is used for situations in which the forcing period is very small compared to the natural time scales of the problem. The simulations show excellent agreement with experimental observations., SCOPUS: ar.j, info:eu-repo/semantics/published

We present a new generic type of pattern generated by bounding walls on the interface between miscible liquids in a horizontally vibrated cell. The pattern is observed in laboratory experiments and numerical simulations below and above the frozen-wave instability threshold. At the threshold, a competition develops between the new "fish-spine" pattern and frozen waves, while above the threshold these two kinds of patterns may coexist in spatially separated domains. We propose a theoretical model for the formation mechanism of the fish-spine pattern and its spreading along the interface., SCOPUS: ar.j, info:eu-repo/semantics/published

We explore the peculiar behaviour of an interface between two miscible liquids of similar (but non-identical) viscosities and densities under horizontal vibration with a frequency less than 25 Hz. Significant differences in the structure of the formed patterns were found between microgravity and ground experiments. In a gravity field, a spatially periodic saw-tooth frozen structure is generated in the interface which dissipates at long times. By contrast, under the low gravity conditions of a parabolic flight, the long lived pattern consists of a series of vertical columns of alternating liquids. This journal is © The Royal Society of Chemistry., SCOPUS: ar.j, info:eu-repo/semantics/published

We present experimental evidence of the existence of an interfacial instability between two miscible liquids of similar (but non-identical) viscosities and densities under horizontal vibration. A stably stratified two-layer system is composed of the same binary mixture with different concentrations placed in a confined cell (with length twice as large as the height). Unlike the case of immiscible fluids, here, the interface is a transient layer of small but non-zero thickness. In the experiments, the frequency and amplitude were varied within the ranges 2–24 Hz and 1.5–16 mm, respectively. When the value of the oscillatory forcing increases, the amplitudes of the interface perturbations grow continuously, forming a saw-tooth frozen structure. This evolution is also examined numerically. In addition to the solutions of full 3-D Navier–Stokes equations, an averaging approach with separation of time scales is used for situations in which the forcing period is very small compared to the natural time scales of the problem. The simulation of averaged equations provides the explanation of the instability development, the calculations of the full nonlinear equations shed light on the decay of a wavy pattern. The results of numerical modelling perfectly support the experimental observations., SCOPUS: ar.j, info:eu-repo/semantics/published

We present a comprehensive experimental study of isothermal Fickian diffusion in the ternary and binary liquid mixtures of water, ethanol, and triethylene glycol over the entire ternary composition space. 21 ternary mixtures inside the composition triangle have been investigated by means of the Taylor dispersion technique and 30 binary mixtures by Taylor dispersion and/or optical beam deflection in a Soret cell. The scalar binary diffusion coefficient has been determined along all three binary boundaries of the composition space and compared with estimations based on the Stokes-Einstein relation using stick or slip boundary conditions. The four elements of the ternary diffusion matrix and the diffusion eigenvalues were determined over a large portion of the composition triangle. The pseudo-binary diffusion coefficients obtained in Taylor dispersion experiments with either one of the two independent concentrations kept constant are comparable to the two diffusion eigenvalues. One of the two off-diagonal elements of the diffusion matrix is of the same order as the diagonal ones and, hence, not negligible, whereas the other one is approximately one order of magnitude smaller. Where available, our results compare well with literature data. The investigated compositions also comprise the five compositions that are scheduled for microgravity experiments in the ESA DCMIX3 project., SCOPUS: ar.j, info:eu-repo/semantics/published

One of the targets of the experiment IVIDIL (Influence Vibrations on Diffusion in Liquids) conducted on-board ISS was to study the response of binary mixtures to vibrational forcing when the density gradient results from thermal and compositional variations. Compositional variations were created by the Soret effect and can strengthen or weaken the overall density gradient and, consequently, the response to vibrational forcing. We present the results of two experimental runs conducted on-board ISS in the frame of the experiment IVIDIL for low and strong vibrational forcing. The experimental observations revealed that a significant mean flow is set within 2 minutes after imposing vibrations and later in time it varies weakly and slowly due to the Soret effect. A mathematical model has been developed to compute the thermal and concentration fields in the experiment IVIDIL and verify the accuracy of picture processing based on the classical approach used in non-convective systems with the Soret effect. The effect of temperature and concentrations perturbations by joint action of vibrational convection and Soret effect on long time scale are carefully examined. The model demonstrates that image processing used for non-convective systems is suitable for the systems with vibration-affected thermodiffusion experiment., info:eu-repo/semantics/published

Pure surface-tension-driven flow is a unique type of flow that can be controlled through external manipulation of thermal and/or mechanical boundary conditions at the free liquid surface where the entire driving force for the convection is generated. This unique feature has been exploited in recent studies for the active control of the flow instability. The use of forced coaxial gas streams has been proposed as a way to stabilize the Marangoni convection in liquid bridges in the planned space experiment JEREMI (Japanese and European Research Experiment on Marangoni Instabilities). It is aimed at understanding the mechanism of the instability and the role of the surface heat transfer and surface shear stresses. This overview presents corresponding preparatory experimental and numerical studies., SCOPUS: ar.j, info:eu-repo/semantics/published

The values of transport coefficients near a critical point are typically enhanced compared to the values in the classical region far away from a critical point. We report on the impact of the asymptotic behavior of the mass diffusion near the critical region on the Soret separation of the components in a model binary mixture. Concentration patterns are numerically investigated in the case of a spatially varying temperature. The Soret separation in ordinary mixture leads to the establishing of a linear concentration distribution in a steady state. The presence of the critical point redistributes the concentration field, it creates a thin layer with sharp concentration change at the critical region which can be seen as a horizontal plateau on vertical profiles. Large concentration gradients are established across this layer. The analysis showed that the kinetic of the separation significantly depends on whether the critical temperature is inside or outside of the applied temperature region, which is T(cold) ≤ T ≤ T(hot). Critical separation road is suggested for the case when T(cr) is located inside this region, T(cold) ≤ T(cr) ≤ T(hot)., info:eu-repo/semantics/published

There exists an instrument SODI (Selected Optical Diagnostic Instrument) on the ISS where series of the DCMIX (Diffusion Coefficients in Mixtures) experiments are conducted by members of the ESA Topical Team. The study is addressed to the performance of thermal design of SODI instrument for DCMIX configuration. We report the results on the temperature fields which were measured interferometrically both in two ground setups (one thermally optimized; the other one, the engineering model of the ISS SODI-DCMIX experiment: non optimized) and in the ISS experiment itself with the respective numerical simulations. Even though monitoring of the cell with binary mixture THN-nC 12 employs only an interferometer with one wave length instead of two for other cells with ternary mixtures, it gives valuable information about the instrument performance. Temperature and concentration fields observed during the tests in the engineering model are compared with those obtained in laboratory experiments with the same liquid, with numerical simulations and with first results from the ISS in Run, SCOPUS: ar.j, info:eu-repo/semantics/published

We present the results of a numerical study of the thermocapillary (Marangoni) convection in a liquid bridge of Pr= 12 ( n-decane) and Pr= 68 (5 cSt silicone oil) when the interface is subjected to an axial gas stream. The gas flow is co-or counter-directed with respect to the Marangoni flow. In the case when the gas stream comes from the cold side, it cools down the interface to a temperature lower than that of the liquid beneath and in a certain region of the parameter space that cooling causes an instability due to a temperature difference in the direction perpendicular to the interface. The disturbances are swept by the thermocapillary flow to the cold side, which leads to the appearance of axisymmetric waves propagating in the axial direction from the hot to cold side. The mechanism of this new two-dimensional oscillatory instability is similar to that of the Pearson's instability of the rest state in a thin layer heated from below (Pearson, J. Fluid Mech. vol. 4, 1958, p. 489), and it appears at the value of the transverse Marangoni number crMa ⊥ 39 44 lower than that of the Pearson's instability in a horizontal layer ( 48< Ma⊥jcrl < 80, depending on the Biot number). The generality of the instability mechanism indicates that it is not limited to cylindrical geometry and might be observed in a liquid layer with cold gas stream. © 2013 Cambridge University Press., SCOPUS: ar.j, info:eu-repo/semantics/published

We report the results of numerical study of two-phase flows in annulus for different aspect ratios obtained in the frame of the JEREMI experiment preparation. The geometry of the physical problem is a cylindrical and non-deformable liquid bridge concentrically surrounded by an annular gas channel under conditions of zero gravity. Thermocapillary (Marangoni) convection in liquid bridge of Pr 68 is analyzed in the case when the interface is subjected to an axial gas stream. The gas flow is counter-directed with respect to the Marangoni flow. The inlet gas velocity U 0 g, temperature difference ΔT between end rods of the liquid bridge and aspect ratio are the control parameters of the system. In the case when the gas stream comes from the cold side, it cools down the interface to a temperature lower than that of the liquid beneath, and in a certain region of the parameter space that cooling causes instability due to a temperature difference in the direction, perpendicular to the interface. The present study is focused on the influence of the aspect ratio on the existence and characteristic features of the oscillatory regime., SCOPUS: cp.j, info:eu-repo/semantics/published

The experiment IVIDIL (Influence of Vibrations on Diffusion in Liquids) has been performed in 2009-2010 onboard the ISS, inside the SODI instrument mounted in the Glovebox at the ESA Columbus module. 55 experimental runs were carried out and each of them lasted 18 hours. The objectives of the experiment were multi-fold and here we report results for one of them. After each space experiment there is a discussion about the role of onboard g-jitters. The attention is focused on reproducibility of the results, their accuracy and comparison with numerical simulations conducted in exact geometry and using the physical properties of the system. We shortly report on the results of six experiments which were performed in natural environment of the ISS without forced vibrations. Thermodiffusion process in the cells filled with binary mixtures was monitored by means of optical digital interferometry. Perturbations of the diffusion control processes by on-board g-jitters is not observed in nominal regime of the ISS. Perturbations of thermodiffusion process were observed in non-nominal regime of the ISS, e.g. attitude control maneuvers., SCOPUS: cp.j, info:eu-repo/semantics/published

We report the results of numerical and experimental studies of two-phase flows in an annulus. The geometry corresponds to a cylindrical liquid column co-axially placed into an outer cylinder with solid walls. Gas enters into the annular duct and entrains the initially quiescent liquid. The internal column consists of solid rods at the bottom and top, while the central part is a liquid bridge from a viscous liquid and kept in its position by surface tension. Silicone oil 5cSt was used as a test liquid and air and nitrogen as gases. An original numerical approach was developed to study the problem in complex geometry. The flow structure in the liquid is analyzed for a wide range of gas flow rates. © 2011 EDP Sciences and Springer., SCOPUS: ar.j, info:eu-repo/semantics/published

The IVIDIL (Influence of VIbrations on DIffusion in Liquids) experiment was aimed at utilizing the International Space Station for investigating the effects of vibrations on liquid diffusion and thermodiffusion. The SODI-IVIDIL project of ESA is gathering together European, Canadian and Russian researchers with complementary skills to prepare and carry out the experiment, to process the raw data and perform numerical modeling of the phenomena. The experiment IVIDIL started on the October 5, 2009. In total 55 experimental runs were successfully completed by 20 January, 2010. A general description of the ISS facility related to the diffusion experiments and accessible for European researchers is briefly presented and some details about IVIDIL instrument are given. The scientific interest of this short article is focused on one of the objectives of the experiment: performing precise measurements of diffusion and thermodiffusion coefficients for binary mixtures in the absence of gravity. We demonstrate possibility of the experimental environment and report on the first results related to measurements of mass transport coefficients in the mixture with the negative Soret effect: 10% isopropanol (IPA)-90% water. © 2011 Académie des sciences., SCOPUS: sh.j, info:eu-repo/semantics/published