Variety of flow patterns in a liquid bridge subjected to a gas stream

We present an experimental and two-phase computational study of convection in a liquid bridge ([Formula: see text]) that develops under the action of a parallel gas flow. The study focuses on tracking the evolution of hydrothermal waves by increasing the applied temperature difference [Formula: see text] and the temperature of gas moving at the velocity [Formula: see text]. Our experiments revealed certain regularity in the change of oscillatory states with an increase in the control parameters. Above the instability threshold, the nonlinear dynamics passes through three oscillatory regimes, which are repeated in a somewhat similar way at higher values of the control parameters. They are periodic, quasi-periodic with two or three frequencies and multi-frequency state when the Fourier spectrum is filled with clusters of duplex, triplex or higher numbers of frequencies. Three-dimensional numerical simulation, complemented by a deep spectral analysis, sheds light on the evolution of the flow pattern observed in experiments. The developed methodology identified conditions for the existence of a multi-frequency regime such as the presence of a weak low-frequency mode that can modulate strong high-frequency modes, the existence of strong azimuthal modes with different wavenumbers and the [Formula: see text] mode, and the structured combination of peaks in the Fourier spectrum. This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.

Measurement of Diffusion of Atmospheric Gases in a Liquid Perfluoro Compound by Means of an Optical Technique

We report on accurate measurements of Fickian diffusion coefficients in binary mixtures consisting of hydrofluoroether (a perfluoro compound of methoxy-nonafluorobutane or HFE-7100) with dissolved atmospheric gases CO₂, N₂, and O₂ in the limit of an infinite dilution of the gas. We show that the use of optical digital interferometry (ODI) allows the determination of diffusion coefficients of dissolved gases with relatively small standard uncertainties for this class of experiments. In addition, we illustrate the ability of an optical approach to determine the gas concentration. We compare the capacity of four mathematical models, singly used in the literature, to obtain diffusion coefficients by applying them to the processing of a large amount of experimental data. We quantify their systematic errors and standard uncertainties. The temperature behavior of the diffusion coefficients measured in the range of 10 to 40 °C is consistent with the behavior of the same gases in other solvents available in the literature.

European Space Agency experiments on thermodiffusion of fluid mixtures in space

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.

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.

Wall-generated pattern on a periodically excited miscible liquid/liquid interface

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.

Contribution to the benchmark for ternary mixtures: Measurement of the Soret, diffusion and thermodiffusion coefficients in the ternary mixture THN/IBB/nC12 with 0.8/0.1/0.1 mass fractions in ground and orbital laboratories

We have determined the Soret (ST), diffusion (D, and thermodiffusion (DT) coefficients in a ternary mixture of tetralin-isobutylbenzene-n-dodecane with a composition of 0.80/0.10/0.10 by mass fraction at a temperature of 298K. The Soret coefficients were measured in the microgravity experiment DCMIX1 and on the ground by optical digital interferometry (ODI) using two lasers with different wavelengths. The values of the Soret coefficients were determined from the stationary separation of the components using two- and six-parameter fits. The diffusion coefficients were independently measured using the Taylor Dispersion Technique in the ground laboratory, and the thermodiffusion coefficients were derived from known ST and matrix D. The processing of the data from the DCMIX experiment conducted on the International Space Station is discussed in detail. The multi-user design of the on-board instrument causes perturbations in the component separation. Several recommendations are suggested for improving the quality of the microgravity results. For example, we demonstrated that the tomography reconstruction of the 3-D concentration field allows to restore the underestimated component separation resulting from the spatial non-linearity of the temperature field. Furthermore, to avoid errors in component separation due to mass exchange between the working liquid volume and the expansion volume at the top of the cell, we suggest considering the evolution of the separation only in the lower half of the cell. The results of this study displayed reasonable quantitative agreement between the microgravity and ground experiments.