Tatyana Lyubimova

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

Influence of vibrations on thermodiffusion in binary mixture: A benchmark of numerical solutions

Double-diffusive and vibrational convection with the Soret effect is considered in a cubic rigid cell filled with water (90%) and isopropanol (10%), subjected to a temperature difference between opposite lateral walls. Numerical simulations are carried out for g-jitter induced flow. The direction of g-jitter is the same as the residual gravity vector, which is perpendicular to the applied temperature gradient. Along with various combinations of static and oscillatory components, vibrations with two different frequencies are examined: (a) when the period of oscillations is smaller than any characteristic time (viscous, thermal, and diffusion), f=0.2Hz; (b) when the period of oscillations is comparable with viscous time, f=0.01Hz. Component separation due to the Soret effect under these driving actions is analyzed. The concept of time-averaged models is applied for the explanation of the high-frequency results. The interplay between the mean and fluctuating motions is discussed. Three research groups perfor...

IVIDIL: on-board g-jitters and diffusion controlled phenomena

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.

Mechanisms of vibrational control of heat transfer in a liquid bridge

Convective flows in a liquid bridge subject to axial high frequency vibrations are studied on the base of a generalized Boussinesq approach. The generation of mean vorticity in the dynamical skin-layers near the rigid and free boundaries is taken into account, with the help of effective boundary conditions for the mean components of hydrodynamical fields. The role of viscous damping of surface waves in the generation of the mean flows is analyzed. Numerical calculations are carried out by a finite-difference method. The possibilities of the vibrational control of thermocapillary flow and of the orientation of the surfaces of constant temperature are demonstrated.

The Onset and Nonlinear Regimes of Convection in a Two-Layer System of Fluid and Porous Medium Saturated by the Fluid

Abstract The onset of convection and its nonlinear regimes in a heated from below two-layer system consisting of a horizontal pure fluid layer and porous medium saturated by the same fluid is studied under the conditions of static gravitational field. The problem is solved numerically by the finite-difference method. The competition between the long-wave and short-wave convective modes at various ratios of the porous layer to the fluid layer thicknesses is analyzed. The data on the nature of convective motion excitation and flow structure transformation are obtained for the range of the Rayleigh numbers up to quintuple supercriticality. It has been found that in the case of a thick porous layer the steady-state convective regime occurring after the establishment of the mechanical equilibrium becomes unstable and gives way to the oscillatory regime at some value of the Rayleigh number. As the Rayleigh number grows further the oscillatory regime of convection is again replaced by the steady-state convective regime.

Vibration Effect on the Nonlinear Regimes of Thermal Convection in a Two-Layer System of Fluid and Saturated Porous Medium

The effect of high-frequency vibrations on the nonlinear regimes of thermal convection in a two-layer system composed of a horizontal pure fluid layer and fluid-saturated porous layer heated from below is studied in the framework of the average approach. For large porous layer thicknesses it has been found, that at low vibration intensities the evolution of convective regimes with the growth of the Rayleigh number proceeds as follows: stationary regime—oscillatory regime—stationary regime. At high vibration intensities the stationary convective regimes take place at any values of the supercriticality used in the calculations. At close values of the fluid layer and porous layer thicknesses the interaction between the short-wave and long-wave instability modes is investigated. It has been found that at high vibration intensities the ambiguity of the stationary solutions is observed in a certain range of supercriticalities.

Soret separation in a binary liquid mixture near its critical temperature

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 Tcold ≤ T ≤ Thot. Critical separation road is suggested for the case when Tcr is located inside this region, Tcold ≤ Tcr ≤ Thot.Graphical abstract

High-frequency vibration effect on the stability of a horizontal layer of ternary fluid

The effect of small-amplitude high-frequency longitudinal vibrations on the stability of a horizontal layer of ternary fluid is studied in the framework of average approach. Long-wave instability is studied analytically and instability to the perturbations with finite wave numbers is studied numerically. It is found that, similar to the case when vibrations are absent, for ternary fluids there exist monotonic and oscillatory long-wave instability modes. The calculations show that the vibrations lead to destabilization in the case of heating from below and to stabilization in the case of heating from above. Additionally, vibrations influence on the parameter range where long-wave instability is most dangerous. New, vibrational, instability modes are found which leads to the existence of convection in zero-gravity conditions.Graphical abstract

Two-dimensional thermal convection in porous enclosure subjected to the horizontal seepage and gravity modulation

Coupled effect of horizontal seepage and gravity modulation on the onset and nonlinear regimes of two-dimensional thermal buoyancy convection in horizontal fluid-saturated porous cylinder of rectangular cross section with perfectly conductive boundaries is studied. It is shown that gravity modulation makes destabilizing effect. Null-dimensional dynamical system describing supercritical convective regimes is derived. Conditions for existence of stable periodical regimes are defined. It is found that system demonstrates dynamics on a torus which can be either resonant or non-resonant depending on the parameters. Synchronization domains which correspond to the resonant torus existence in the parameter space are determined by the rotation number technique. It is found that at certain values of the ratio of the cross section height to width, degeneracy takes place. In this case different stable periodical regimes forming one-parametric family coexist. Linear stability and nonlinear dynamics of the system at fi...

Stability of a stationary plane-parallel flow of a ternary fluid between two vertical plates maintained at constant different temperatures

Abstract.The linear stability of a steady convective flow of a ternary mixture placed between differently heated vertical rigid plates is studied. The applied temperature gradient induces concentration gradients due to the Soret effect. The analysis is done for the case when separation ratios of ternary mixture, i.e., Soret coefficients, have different signs but the net separation ratio is negative. The stability maps in terms of the Grashof number and net separation ratio are obtained and discussed for monotonic and oscillatory modes of instability. The previous results for long-wave instability of a binary mixture were recovered in the limit when one of the Soret coefficients tends to zero. For finite-wavelength perturbations the previous results were extended by discovering the oscillatory instability.Graphical abstract