On the space diffusion coefficient measurements
- Paper number
IAC-06-A2.2.01
- Author
Dr. Xavier Ruiz, Universitat Rovira i Virgili, Spain
- Coauthor
Dr. Jordi Pallares, Universitat Rovira i Virgili, Spain
- Coauthor
Dr. Francesc Xavier Grau, Universitat Rovira i Virgili, Spain
- Year
2006
- Abstract
As it’s well known the highly accurate measurement of the diffusion coefficients is of capital importance to test the validity of the physics underlying mass transport phenomena. Because of the convection has a pernicious influence on the required accuracy, shear-cells and mg environments seemed to be, since the nineties, a convenient alternative to perform measurements. However mg results are not as precise as it could be expected because of the existence of three types of distorting agents acting together in real environments. The first one is related with the interaction between the concentration gradients and the residual mg vector . Particularly important is the impact of the g-jitter –an unavoidable characteristic of any spatial platform- on these kind of experimental measurements [1, 2]. The second disturbing agent is related with the shearing process during the joining and separation periods [3, 4]. Finally, the third one related to the also unavoidable existence of natural convection linked to the thermal gradients – radial and axial- inside any cell at high temperature [5]. The present theoretical approach, using accurately controlled virtual gravity environments, will discuss the impact of the above-mentioned potential factors on the diffusion coefficient measurements. To quantify this impact, the percentage of error, %D(t) = 100 (D*(t)-D) / D generated by convective contamination will be introduced. Here D*(t) is the apparent convective diffusion coefficient based on the calculation of the slope of the {x, 2 t-.5 erf-1 (-2C(t,x)} linear fitting, x is the position of the geometrical center of each one of the different cell segments, t is the time, erf-1 is the inverse of the Gauss error function, C(t,x) is the segment-averaged computed concentration and D is the value of the diffusion coefficient used in the numerical resolution of the corresponding mass and momentum transport inside the cell by the finite volume method. To extent as much as possible the final conclusions, two kind of generic liquid systems in the range of semiconductors and liquid metals will also be considered.
[ [1] G. Mathiak, E. Plescher, R. Willnecker, Measur. Sci. and Technol, 16 (2005) 336. [2] R.W. Smith, B.J. Yang, Proceedings of the Interdisciplinary Transport Phenomena in Microgravity and Space Sciences Conference IV, Tomar, Portugal, August 2005. [3] G. Mathiak, G. Frohberg, W.A. Arnold, Proc. Second European Symposium Fluids in Space, Naples, Italy, April 1996. [4] B.J. Yang, R.W. Smith, J. Phys.: Condensed Matter 15 (2003) 3855. [5] D. J. McLean, T. Alboussière, Int. J. Heat Mass Transfer 44 (2001) 1639.]
- Abstract document
- Manuscript document
IAC-06-A2.2.01.pdf (🔒 authorized access only).
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