Observation of diffusion phenomena in ground experiments: problems and solutions.

Paper number

IAC-06-A2.4.05

Author

Dr. Valentina Shevtsova, Université Libre de Bruxelles, Belgium

Coauthor

Dr. Alexandr Mialdun, Université Libre de Bruxelles, Belgium

Coauthor

Mr. Denis Melnikov, Université Libre de Bruxelles, Belgium

Year

2006

Abstract

The future Space experiment IVIDIL is planned to study the influence of vibration stimuli on the measurements of diffusion and thermodiffusion coefficients. The objective of the project is to improve our understanding of the kinetic mechanisms that are driven by diffusion in presence of vibrations. Presently the ground based preparatory experiments are running at ULB.  

A new experimental set-up was designed to study heat and mass transfer in liquids with Soret effect. The experiments are performed in a transparent cell filled initially by a homogenous mixture. In the experimental cell heated top and cooled bottom walls impose the thermal gradient. The spatial variation of the temperature induces mass flow through the Soret effect.  An enlarged collimated laser beam traverses the entire cell parallel to the plates.   Both temperature and composition variations contribute to create a spatial distribution of the refractive index that modulates the wave-front of the emerging optical beam. The optical interferometer coupled to a digital recording and processing is used for very accurate determination of the optical amplitude and the phase information. The processing of images gives information about the local gradients of composition inside of the fluid both for steady state and dynamic regimes.
Despite the heating from above, buoyant convection in the cell can occur in the laboratory experiments for the considered range of temperature difference. Actually it is one of the reasons why the diffusion and Soret coefficients will be measured in Space. The microgravity environment minimizes the effect of gravity and allows the true diffusion limit to be achieved.

This question of diminishing the buoyancy-induced flows was seriously analyzed with support of 3D numerical simulations. The outcome of that study showed that the major reason for the appearance of convection is the heat transfer at corner junction points: liquid, glass, and copper. The detail analysis of the thermal design will be presented.

Abstract document

IAC-06-A2.4.05.pdf

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