Optimization of Taylor Dispersion Technique for Measurement of Mutual Diffusion in Benchmark Mixtures

The Taylor dispersion technique has been used for measuring binary mutual diffusion coefficients for mixtures of 1,2,3,4-tetrahydronaphthalene (THN), isobutylbenzene (IBB) and dodecane (C₁₂ H ₂₆) at 0.5:0.5 mass fraction symmetric points, and for 0.9:0.1 mass fraction in IBB- C₁₂ H ₂₆. From the Stokes–Einstein equation and our experimental results, the limiting diffusion coefficients, D ⁰, and the equivalent solvated radii, R _s, have been estimated at infinitesimal concentration of these species (TNH, IBB and C₁₂ H ₂₆). The measured diffusion coefficients are used to estimate activity coefficients of the components in the mixture, contributing to a better understanding of the structure of such systems and of their thermodynamic behaviour at different concentrations. We have also investigated the diffusion properties for a ternary system containing equal mass fractions of all the components (0.33THN: 0.33IBB: 0.33C₁₂ H ₂₆) and at 298.15 K.     

Giant vortex structures in mesoscopic spherical type-II superconducting samples

Giant vortex states which can occur in type-II mesoscopic spherical superconducting samples embedded in different materials have been studied within the framework of the nonlinear Ginzburg–Landau theory. The proposed method, which is based on presentation of the superconducting order parameter in a form of the spherical functions expansion gives the possibility to take into account different types of boundary condition.     

Structure clusterization preceding concentration phase transitions

The formation and development of bulk crystallochemical defects—mesoscopic clusters representing the nuclei of new phases—was studied in systems exhibiting concentration phase transitions. When a solid solution approaches a morphotropic region, the clusters exhibit a stepwise evolution involving several stages manifested by corresponding changes in macroscopic properties. The role of clusters in the development of the extreme electrophysical properties of the objects studied is discussed.     

Growth in the velocity of mass transfer through the CMX membrane during its aging by operation in intense current regimes

One of the causes for the aging of membranes during their operation in electrodialysis (ED) of solutions is irreversible chemical changes in the ion exchange or reinforcement polymer due to interaction of H⁺ and OH⁻ ions (present in feed solutions or generated in the membrane system under intense current modes) with the matrix or fixed groups in the surface layer of the membranes. The reduction in current efficiency and an increase in energy consumption in the process of electrodialysis are usual consequences of these changes. It has been shown that the degradation of the ion-exchange polymer on the surface of the CMX membrane during its operation in intense current regimes results in the hydrophobization of the membrane surface, which, in turn, causes enhancement of electroconvection. As a result, the limiting current and the mass transfer coefficient of salt ions increase during membrane operation. In the case of desalination of dilute solutions, this growth can reach 50–70% in comparison with the fresh membrane.     

Experimental Study on Formation of Particle Accumulation Structures by a Thermocapillary Flow in a Deformable Liquid Column

A series of experiments has been performed under earth’s gravity to study formation of particle accumulation structures (PAS) in a supercritical flow driven by the combined effects of buoyancy and thermocapillary forces. The test flow was created in a non-isothermal cylindrical column (liquid bridge) made of n-decane and heated from above. The objective of the experiment was to answer two major questions: (1) how strong is the influence of the shape of the interface on the process of formation of PAS; (2) what temperature of the ambient air fits better for PAS to occur. Considering these questions, we developed a method based on changing both the volume of the liquid bridge and temperature at the external walls of the experimental chamber to set and to keep constant the shape of the interface and the temperature inside the setup, respectively. The experimental observations are presented in the form of diagrams in the parameters’ space showing ranges of the PAS formation. The findings show that a liquid bridge with an interface as close to the straight cylindrical as possible and surrounded by air at low temperature is the best terrain for PAS formation. The results of the chaos analysis of the recorded temperature time series and their correlation with the obtained diagrams allow for showing that accumulation of particles in coherent structures is possible only in a periodic oscillatory flow characterized by a small value of the translation error not exceeding 0.01. It is demonstrated that presence of either any spectral noise or of several modes with incommensurate frequencies makes formation of a PAS impossible.     

Effect of the form of the temperature dependence of surface tension on motion and heat transfer in a layer of liquid during local heating

The nonsteady distribution of velocity and temperature in a layer of liquid during thermoconvective motion caused by local heating is calculated. The cases of an increasing and decreasing temperature dependence of surface tension are examined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 1, pp. 27–33, July, 1989.     

Analysis of the Thermal Performance of SODI Instrument for DCMIX Configuration

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 #16. The thermal design of the microgravity cell, being not optimized for ground experiments, exhibits a promising performance in the weightlessness condition.     

Thermocapillary convection in a liquid bridge subjected to interfacial cooling

Influence of heat loss through interface on a supercritical three-dimensional thermoconvective flow in a long liquid bridge is numerically investigated under terrestrial conditions. A flow in a high Prandtl number liquid surrounded by an ambient gas of constant temperature is simulated for the large aspect ratio, Γ=1.8. It is shown that the heat loss plays a significant role in the flow dynamics. It modifies both the flow and the liquid temperature field. Moreover, for the relatively large aspect ratio and a high Prandtl number liquid the heat loss from interface leads to destabilization of the flow.