GRADFLEX: The Microgravity Experiment for Gradient Driven Fluctuations
- Paper number
IAC-05-A2.6.01
- Author
Mrs. Barbara Hirtz, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Antonio Verga, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Roberto Cerbino, Universita di Milano and CNR-INFM, Italy
- Coauthor
Mr. Stefano Mazzoni, Universita di Milano and CNR-INFM, Italy
- Coauthor
Mr. Marzio Giglio, Universita di Milano and CNR-INFM, Italy
- Coauthor
Mr. Ralf Greger, Switzerland
- Year
2005
- Abstract
Fluids or fluid mixtures are subject to random thermal motion: fluctuations in local density and temperature (and concentration in case of a mixture) are always present, also for fluids in thermodynamic equilibrium, although quite different from non-equilibrium systems. In the latter case, fluctuations assume a typical oscillatory behaviour. It has been predicted and measured by various experiments that the amplitude and the correlation range of the fluctuations are greatly enhanced if a fluid is stressed by a temperature and/or concentration gradient. Additionally, it has been shown that gravity plays a significant role especially at the long wavelengths: the power spectra of the fluctuations show a q −4 dependence (where q is the spatial wave vector of the fluctuations i.e. a frequency). Towards small wave vectors the amplitude is hampered by gravity to a constant value. Thus, experiments in weightlessness should produce very large fluctuations with much longer time scales and length scales approaching the size of the sample container.
The research on non-equilibrium fluctuations is mainly of fundamental character. One field of interest may be in applications such as crystal growth in microgravity environments: the growth process generates concentration gradients and thus highly enhanced fluctuations, which may influence the very structure of the crystal.
An apparatus called the Gradient Driven Fluctuation Experiment (GRADFLEX) is therefore designed to measure these non-equilibrium fluctuations in microgravity conditions. GRADFLEX is poised to fly on-board FOTON M-3 in fall 2006. FOTON – well known for its excellent microgravity levels – is an automatic Russian spacecraft that is launched to low Earth orbit by a Soyuz-U launch vehicle and is returned to Earth after its 12 to 16 day mission.
GRADFLEX is hosting two individual experiments: the SINGLE experiment dealing with an organic single-component fluid (carbondisulphide) stressed by a pure temperature gradient and the MIXTURE experiment that investigates a fluid mixture (9100 molecular weight polystyrene in toluene) under the combined effect of a temperature and concentration gradient whereas the concentration gradient is imposed by thermal diffusion (Ludwig-Soret effect).
Variations in density or concentration scatter light. An optical method such as Quantitative Shadowgraphy has been identified as the measurement technique of choice, being non-invasive and highly sensitive.
This paper outlines the main design features of GRADFLEX, its optical instruments and experiment layouts, as well as its foreseen operational scenario during the FOTON-M3 flight.
- Abstract document
- Manuscript document
IAC-05-A2.6.01.pdf (🔒 authorized access only).
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