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Trends in Heat & Mass Transfer   Volumes    Volume 7 
Abstract
Impact of gravity level on double diffusive instability
D. Castagnolo, F. Albano, L. Carotenuto, R. Monti, R. Savino, V. Vitagliano
Pages: 1 - 18
Number of pages: 18
Trends in Heat & Mass Transfer
Volume 7 

Copyright © 2001 Research Trends. All rights reserved

ABSTRACT

Space orbiting laboratories give the unique opportunity to carry out Physical Sciences experiments in a microgravity environment where the intensity of gravity is reduced by several orders of magnitude (e.g about 10-6 times the value g0=9.81 m/s2 present on Earth). Experiments for the measurement of diffusion coefficients are examples of processes with high microgravity relevance, that would require purely diffusive regimes (i.e. quiescent or quasi-quiescent conditions) to eliminate or strongly reduce the unavoidable convective flows induced, on Earth, by the interaction of the gravity with density gradients induced by temperature or concentration gradients.

Purpose of this paper is to describe ground-based experimental activities and numerical simulations carried out in preparation of a microgravity experiment that will be performed on board the International Space Station.

Objective of this experiment is the measurement of diffusion coefficients in a three-component solution characterized on ground by double-diffusion convective instabilities (fingering or overstability). To carry out this measurement, an interferometer will be used to measure the solution concentration gradient at different times.

The configuration investigated under normal gravity consists of a “vertical” diffusion cell with a solution initially heavier at the bottom and lighter at the top. Different initial conditions for the concentrations are considered leading, on ground, to salt “fingers” instabilities or to “overstability”. Numerical simulations have been carried out to reproduce the experimental conditions.

The time evolution of the concentrations are compared to the results corresponding to the “ideal” purely diffusive conditions and to the real microgravity conditions expected during the UF#3 mission of the ISS.

The measurements will be done at different orientations of the cell with respect to the residual acceleration vector, using an appropriate device to minimize the convective disturbances.

The paper discusses the expected results from the ISS experiments and the results of the numerical simulations and of the ground experiments.
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