Experimental study of thermo-vibrational convection in reduced gravity

Paper number

IAC-08.A2.2.4

Author

Dr. Valentina Shevtsova, Université Libre de Bruxelles, Belgium

Coauthor

Dr. Aliaksandr Mialdun, University of Brussels, Belgium

Coauthor

Dr. Ilya Ryzhkov, University of Brussels, Belgium

Coauthor

Dr. Denis Melnikov, University of Brussels, Belgium

Coauthor

Dr. Yury Gaponenko, University of Brussels, Belgium

Year

2008

Abstract

The study of convection, forced by external vibrations, and associated heat transport is presented. A homogeneous liquid of constant density moves together with the cell as a solid body when the system is subjected to external vibrations. The appearance of relative flow is due to density variations. The most evident way to create the density gradient in homogeneous liquid system is applying temperature gradient to the liquid. The resulting motion in the liquid is called thermo-vibrational convection. Vibrational convection provides a mechanism of heat and mass transfer due to the existence of mean flows. In weightlessness, it is an additional way of transporting heat and matter similar to thermo- and solutocapillary (Marangoni) convection. 
Vibration can suppress or intensify gravitational convection depending on the mutual orientation of vibration axis and thermal (compositional) gradient. The pure thermo-vibrational effect can be observed in weightlessness only. In terrestrial conditions, the static gravity strongly masks thermo-vibrational convection. However, experimental studies addressing vibrational phenomena in weightlessness are very limited. 
We present the results of experiments on the observation of thermal vibrational convection in reduced gravity, conducted in the 46th and 48th Parabolic Flight Campaigns organized by the European Space Agency. For the first time we report an experimental evidence of thermo-vibrational convection caused by translational vibration of non-uniformly heated fluid in low gravity.
In the experiments, a transparent cubic cell (5 mm in size) is filled with isopropanol and the temperature difference is applied between two horizontal walls.  The cell is fixed to a linear motor, which performs translational harmonic oscillations in the direction perpendicular to the temperature gradient. The thermovibrational flows were monitored by measuring the temperature field inside the cell by optical digital interferometry. 

On-board experiments were performed for various combinations of gravity and vibrations: a) study of convection in microgravity without vibrations; b) study of convection in microgravity with vibrations; c) study of convection in normal gravity (horizontal flight) with and without vibrations. Through the evolution of temperature field we observed that the strongest convection occurs in microgravity with vibrations. Thus, we demonstrated that translational vibrations create relatively large mean flows, which is stronger then current, created by buoyant convection due to residual gravity.  The obtained results show that mean vibrational flows can cause strong heat transport in the fluid. It was found that this transport becomes more intensive with increasing the vibrational impact.

Abstract document

IAC-08.A2.2.4.pdf

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