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.

Gradient-driven fluctuations in microgravity.

Equilibrium fluctuations of thermodynamic variables, such as density or concentration, are known to be small and typically occur at a molecular length scale. In contrast, theory predicts that non-equilibrium fluctuations grow very large both in amplitude and spatial size. On earth, the presence of gravity and buoyancy forces severely limits the development of the fluctuations.

Thermal fluctuations in a layer of liquid CS2 subjected to temperature gradients with and without the influence of gravity.

We report data for nonequilibrium density fluctuations in a layer of liquid CS(2) subjected to temperature gradients on Earth and in a satellite. The structure factor S(q) was measured using a calibrated shadowgraph. Upon removing gravity, S(q) increased dramatically at small wave vector, until the fluctuations generated by thermal noise were limited only by the 3 mm sample thickness.

Fractal fronts of diffusion in microgravity.

Spatial scale invariance represents a remarkable feature of natural phenomena. A ubiquitous example is represented by miscible liquid phases undergoing diffusion. Theory and simulations predict that in the absence of gravity diffusion is characterized by long-ranged algebraic correlations.

Dynamics of long-wavelength fluctuations in a fluid layer heated from above.

We report an experimental study of the dynamics of thermal fluctuations in a 4.86 mm thick layer of CS2 heated from above. Stabilizing gradients ranged from 10.