Aliaksandr Mialdun

A comprehensive study of diffusion, thermodiffusion, and Soret coefficients of water-isopropanol mixtures

We report on the measurement of diffusion (D), thermodiffusion (D(T)), and Soret (S(T)) coefficients in water-isopropanol mixtures by three different instrumental techniques: thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, and optical digital interferometry. All the coefficients have been measured over the full concentration range. Results from different instruments are in excellent agreement over a broad overlapping composition (water mass fraction) range 0.2 < c < 0.7, providing new reliable benchmark data. Comparison with microgravity measurements (SODI/IVIDIL (Selected Optical Diagnostic Instrument/Influence of VIbration on DIffusion in Liquids)) onboard the International Space Station and with literature data (where available) generally gives a good agreement. Contrary to theoretical predictions and previous experimental expectations we have not observed a second sign change of S(T) at low water concentrations.

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

Investigation of Fickian diffusion in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane

We present a comprehensive analysis of experimental results obtained for Fickian diffusion in the benchmark ternary liquid mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane (nC12) with equal mass fractions. Isothermal diffusion coefficients have been measured by two independent experimental methods: by Taylor dispersion technique, and by a counter flow cell fitted with an optical interferometry device. The experimental diffusion matrices have been critically analyzed regarding the Onsager reciprocal relations, for which we introduce a matrix asymmetry index s(2) that is independent of the frame of reference and the component order.

Experimental and theoretical study of vibration-induced thermal convection in low gravity

Vibrations acting on a fluid with density gradient induced by temperature variations can cause relative flows. High-frequency vibration leads to the appearance of time-averaged (mean) flows (or streaming flows), which can essentially affect heat and mass transfer processes. This phenomenon is most pronounced in the absence of other external forces (in particular, static gravity). In this work, an extensive experimental and computational study of thermal vibrational convection in a reduced-gravity environment of a parabolic flight is performed. The transient evolution of the temperature field in a cubic cell subjected to translational vibration is investigated by optical digital interferometry. The mean flow structures previously reported in numerical studies are confirmed. The transition from four-vortex flow to a pattern with a large diagonal vortex and two small vortices is observed in the transient state. The experiments reveal a significant enhancement of heat transfer by vibrational mean flows with increasing the vibrational strength. Three-dimensional direct numerical simulation with real microgravity profile and two-dimensional numerical modelling based on averaging approach provide a very good agreement with the experimental results. The influence of residual gravity on heat transfer and bifurcation scenario is first investigated numerically and correlated with the experimental data. It is demonstrated that gravity effects on non-uniformly heated fluids can be reproduced in weightlessness by applying vibrations to the system.

A study of heat transfer in liquid bridges near onset of instability

Abstract The appearance and development of thermoconvective oscillatory flows are investigated experimentally with numerical support in a liquid bridge of aspect ratio Γ = 1.2 filled with 5- and 10-cSt silicone oils and subjected to a temperature difference ΔT. The experiments with high Prandtl number fluids were carried out under terrestrial conditions for a wide range of volumes of liquid bridges in open air and with shielding. For the experiments in open air, the temperatures of the gas and liquid close to the interface remain practically constant along most of the interface. Moving across the interface, i.e., from the liquid to the gas, a temperature ‘‘jump’’ is found with 0.4ΔT ≈ 9 K over a distance of less than 1 mm for slender liquid bridges. This tendency remains valid for fat liquid bridges. This sharp temperature drop represents additional disturbances in destabilizing the system. The flow is steady and axisymmetric at suffciently low values of ΔT. The magnitude of ΔT at which the flow becomes oscillatory depends on the relative volume of the liquid and on the external conditions. To better understand the influence of the thermal conditions of the surroundings on transition to oscillations, the experiments were carried out under two different conditions: in an open-air environment and in shielded liquid bridges. In this way, different heat transfer possibilities at the free surface are realized. Complementary numerical calculations were also performed to support our explanations of the experimental observations.

Communication: New approach for analysis of thermodiffusion coefficients in ternary mixtures

A new approach is proposed to cross-check conflicting measured values of the thermodiffusion coefficients in ternary mixtures. The results of recent measurements performed in ternary mixture of hydrocarbons 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane by thermogravitational column [P. Blanco, M. M. Bou-Ali, J. K. Platten, D. A. de Mezquia, J. A. Madariaga, and C. Santamaría, J. Chem. Phys. 132, 114506 (2010)] and optical beam deflection [A. Königer, H. Wunderlich, and W. Köhler, J. Chem. Phys. 132, 174506 (2010)] are critically analyzed. A way of matching them into a unique value is reported. The accuracy of the integrated value should significantly exceed that of the original results. Two diagnostics are required to determine thermodiffusion coefficients in ternary mixture, e.g., two different wavelengths or density and refractive index. It is shown that by attributing a reliability weight for each pair of diagnostics among the available techniques the best combination can be selected. The true values of thermodiffusion coefficients are extremely sensitive to the knowledge of precise values of mass diffusion coefficients and contrast factors.

Fickian Diffusion in Ternary Mixtures Composed by 1,2,3,4-Tetrahydronaphthalene, Isobutylbenzene, and n-Dodecane.

We report the Fickian diffusion coefficients in 20 ternary mixtures formed by 1,2,3,4-tetrahydronaphthalene (THN), isobutylbenzene (IBB) and n-dodecane (nC12) measured by the Taylor dispersion technique at 298.1 K and atmospheric pressure. Four diffusion coefficients of the ternary mixtures were measured along six concentration paths starting on one binary subsystem and moving toward the other one. We found expressions for the diffusion matrix of a ternary mixture approaching to the binary limits. The measured diffusion coefficients were thoroughly verified by comparison with the theoretical asymptotic behavior. The main diffusion coefficients vary smoothly over the entire concentration space and D11 is always larger than D22. One of the two cross-diffusion coefficients is of the same order of magnitude as the main ones and, hence, not negligible, whereas the other one is close to zero. The investigated mixtures also comprise compositions that were examined in microgravity experiments in the ESA DCMIX1 project.

Peculiarity of 3D Flow Organization in Soret Driven Instability

Abstract Three-dimensional time-dependent numerical calculations are performed in a cubic cell filled with a binary mixture of water (90%) and isopropanol (10%). The system is heated from above while the Soret coefficient (ST ) is negative, i.e., a thermally stable Rayleigh-Benard configuration. Due to the Soret effect, the heavier liquid is accumulated on the top of the lighter one and buoyant convection can be initiated. We report the numerical value of critical solutal Rayleigh number Ras ≈ 16200 at which motion starts in a cubic cell. The flow has a finger (or columnar) structure where the major mass flux is concentrated near the center line. Later in time, this columnar structure diffuses in the horizontal direction. The development of the motion is shown through the evolution of 3D flow patterns. The upward or downward direction of the flow along the center line depends on the applied temperature difference. We attribute the change in direction of the motion to the finite size of the system and to the features of Rayleigh–Benard convection in a cubic cell.

Interfacial pattern selection in miscible liquids under vibration

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.

The effect of alcohols as the third component on diffusion in mixtures of aromatics and ketones

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.