Diffusion and Soret in Ternary Mixtures. Preparation of the DCMIX2 Experiment on the ISS

Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures

“…In order to induce a strong sedimentation in this mixture we need to increase the ratio m 2 g/ (k B T ) by six orders of magnitude relative to its reference value on Earth (see (B2)). In actual experiments this would be accomplished by increasing the effective gravity (i.e., centrifugal acceleration) in an ultracentrifuge; however, increasing gravity by such a large factor makes the system of equations (3,5,30) numerically too stiff for our semi-implicit temporal integrator. This is because buoyancy changes the time scale for relaxation of large-scale (small wavenumber) concentration fluctuations from the usual slow diffusive relaxation to a very fast non-diffusive relaxation [45].…”

“…We focus our investigation here on the differences in the spectrum of the thermal fluctuations with (unstable) and without (marginally stable) gravity. Note that experimental measurements of giant concentration fluctuations in microgravity are feasible and have been performed for binary liquid mixtures [8]; microgravity measurements on ternary mixtures are ongoing or in the planning stage [3].…”

“…Furthermore, the quasi-two dimensional geometry limits the possibilities for interactions between the fluctuations and the instability. For this reason, we also reported simulations of diffusive layer convection for a three-dimensional ge- An important challenge for experimental physicists is to devise ways to measure the thermophys-ical properties in multispecies mixtures [3]. While our formulation can handle mixtures of arbitrary numbers of species with essentially complete physical fidelity, it is not possible to use our codes for realistic non-dilute mixtures because many of the parameters, notably the thermodynamic factors and the Maxwell-Stefan diffusion coefficients, are missing.…”

“…Part of the difficulty is in the increased complexity of the formulation of multispecies diffusion and the increased difficulty of obtaining analytical results, as well as the far greater complexity of experimentally measuring transport coefficients in multispecies mixtures. In fact, experimental efforts to characterize the thermo-physical properties of ternary mixtures are quite recent and rather incomplete [3].…”

Editorial: Thermal non-equilibrium phenomena in multi-component fluids

“…In this Topical Issue, the reader will find a total of seven papers devoted to this benchmark: six "contribution" articles [4][5][6][7][8][9] plus one summarizing all the experimental data contained in the other papers and providing an average value for the quantities of interest [10]. The experiments took place within the cooperative framework of the international project DCMIX (Diffusion Coefficients in ternary MIXtures), representing a significant investment by national and international space agencies such as ESA, NASA, CSA and ROSCOSMOS that should benefit the community at large [11].The present Topical Issue is complemented by another 17 papers. Their subjects are listed here, in no particular order.…”