Projet de recherche PX/7/LP/34 (Action de recherche PX)
In the frame of the ESA MAP Physical Sciences project "Diffusion and Soret Coefficient Measurements for Improvement of Oil Recovery", (or DSC) the experiment IVIDIL is planned to examine the influence of vibration stimuli on the diffusive phenomena.
Molecular diffusion occurs when a concentration gradient exists in a mixture: there is a net mass flux that tends to decrease the magnitude of this concentration gradient. To describe the effect of temperature gradients on the separation of the components, the thermodiffusion process also called Soret effect is considered.
The knowledge of transport properties in liquid mixtures has important industrial applications. Petroleum exploration and production companies are demanding very accurate values of diffusion and thermodiffusion coefficients for their sophisticated thermodynamic numerical models. The transport coefficients in gases can be rather well estimated by kinetic theory but the situation is less favorable for liquid mixtures. Thermal diffusion in liquids is not so well understood even for binary mixtures. So, the experimental methods play an important role in the determination of the transport coefficients in liquids.
Precise measurements of diffusion coefficients under terrestrial conditions are often perturbed by buoyancy-induced flows. The microgravity environment minimizes the effect of gravity and allows the true diffusion limit to be achieved. On the other hand the background g-jitter encountered in many space experiments may alter the benefits of the microgravity environment. Previous experiments on-board the Mir station using the Canadian MIM platform, indicated that the values of the measured diffusion coefficients in dilute binary metallic alloys depend upon the residual accelerations and the quality of microgravity.
Thus a study of the effects of controlled vibrations on the measurements of diffusion and Soret coefficients in liquid systems could be beneficial. The scientific team suggests to perform the experiments in two steps. During the first step a concentration gradient is established by imposing a temperature gradient along the experimental cell that is filled with a homogeneous binary mixture. Due to Soret effect, the binary mixture tends to separate with time. At the second step the system is reverted to an isothermal case, and molecular diffusion will progressively reduce the previously established concentration gradient. Thus there is an exceptional opportunity to measure the Soret coefficient during the first step and the molecular diffusion coefficient during the second step. One of the significant benefits of this scheme is the absence of mechanically driven parts in contact with the liquid (no valves, curtains, etc.). Moreover such an approach allows repetition of the experiments to study exactly the same system with identical or different vibration parameters. In this way the reliability of the experiments will be improved in an important way by the use of statistical techniques. Ground-based experiments are presently conducted in MRC, ULB to test and improve data acquisition technique. A specially designed prototype is used, which includes a Mach-Zehnder interferometer to follow the concentration distribution inside mixture.
Preliminary parametric analysis of the most dangerous frequencies and g-jitter amplitudes are also conducted numerically. Numerical support of the IVIDIL experiment is provided by several teams: the Microgravity Research Center, ULB, Belgium (MSL); Ryerson University, Toronto, Canada (YS) and CNRS-Universités d'Aix-Marseille, France in collaboration with a Russian team from Perm (LSR). Each team has experience with calculation of convective flows under vibrations.
Satellite(s) or flight opportunity(ies):
- SODI in the Microgravity Science Glovebox on the International Space Station
Field of research:
Physical Science: Fluid Physics
