| Autor: |
K. Wollhöver, Ch. Körber, M.W. Scheiwe |
| Rok vydání: |
1983 |
| Předmět: |
|
| Zdroj: |
International Journal of Heat and Mass Transfer. 26:1241-1253 |
| ISSN: |
0017-9310 |
| DOI: |
10.1016/s0017-9310(83)80179-3 |
| Popis: |
An analysis of solute redistribution in binary aqueous salt solutions during unidirectional freezing with a planar solid-liquid interface is presented. A cryomicroscope was equipped with a specially designed freezing stage yielding a well-defined temperature distribution and interface propagation kinetics similar to large systems of plate-like geometry. A microscope spectrophotometer was attached for concentration measurements by means of transmitted light. Aqueous solutions of NaMnO4, exhibiting a maximum absorption at 525 nm and having a phase diagram, as well as mass diffusion properties, very similar to NaCl in water, were used as sample solutions. A major advantage of the method is the combination of quantitative measurements and observation allowing a visual control of the shape of the ice front, and hence of the transition from planar freezing to higher structures. Photometricscans of concentration profiles were recorded duringone-dimensional freezing with interface propagation rates between 1 and 10 μm s−1. It was shown that the ‘steepness’ of the concentration distributions increased with both time and growth velocity. During the initial transient, the results agree well with amathematical model describing pure mass diffusion at constant ice front velocity. Instabilities of the planar interface resulting in dendritic breakdown always occurred before eutectic or steady-state conditions were reached. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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