Simulation of directional solidification, thermochemical convection, and chimney formation in a Hele-Shaw cell

It is recognized that flow in the melt can have a profound influence on the dynamics of a solidifying interface and hence on the quality of the solidified material. To better understand the effect of fluid flow on the interface morphological stability and on the cellular and dendritic growth, directional solidification experiments were carried out in a horizontally placed Hele-Shaw cell with and without externally imposed parallel shear flow. The specimen material used was SCN–1.0 Wt% acetone. The experiment shows that the transient parallel flow has a stabilizing effect on the planar interface by damping the existing initial perturbations. The left–right symmetry of crystal cells was broken by the parallel flow, with cells tilting toward the incoming flow direction. The tilting angle increased with the velocity ratio. The secondary dendrites were found to either not appear or appear much later on the downstream side of the crystal cells. The wavelengths of the initial perturbations and of the cellular interface were insensitive to the imposed flow.

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The interactive dynamics of flow and directional solidification in a Hele-Shaw cell Part 2. Stability analysis and nonlinear simulations

Journal of Fluid Mechanics ◽

10.1017/s0022112002001933 ◽

2002 ◽

Vol 470 ◽

pp. 269-290

Author(s):

SUDHIR S. BUDDHAVARAPU ◽

ECKART MEIBURG

Keyword(s):

Stability Analysis ◽

Directional Solidification ◽

Linear Stability ◽

Linear Stability Analysis ◽

Flow Model ◽

Nonlinear Simulations ◽

Interactive Dynamics ◽

Predicted Values ◽

Potential Flow Model ◽

Hele Shaw Cell

A linear stability analysis as well as nonlinear simulations are performed in order to analyse the coupling between the directional solidification of a binary alloy and the flow in its melt. An incompressible, potential flow model is assumed, whose validity is tested through comparisons with the accompanying experiments of Zhang & Maxworthy (2002) in a Hele-Shaw cell. The linear stability analysis predicts that a uniform flow parallel to the interface reduces the growth rates of directional solidification instabilities. In addition, the dominant wavelength is shifted to larger values by the flow, and a small propagation velocity in the downstream direction is observed. These findings are confirmed by the nonlinear simulations as well. While the overall stabilization is confirmed by the experiments, the predicted values of the dominant wavenumber and its growth rate are too high by factors of two and four, respectively. These differences are attributed to the existence of a velocity boundary layer in the melt, which strongly affects the lateral solute transport.

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Viscosity Effects on the Directional Solidification of NH4Cl Solution in a Hele-Shaw Cell

Physics of Fluids A Fluid Dynamics ◽

10.1063/1.4738867 ◽

1992 ◽

Vol 4 (9) ◽

pp. 1879-1879 ◽

Cited By ~ 1

Author(s):

C. F. Chen

Keyword(s):

Directional Solidification ◽

Viscosity Effects ◽

Nh4cl Solution ◽

Hele Shaw Cell

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The effect of back-melting on the continuity of crystallographic orientation and composition in HgZnTe

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133114 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1696-1697

Author(s):

H.J. Zuo ◽

M.W. Price ◽

R.D. Griffin ◽

R.A. Andrews ◽

G.M. Janowski

Keyword(s):

Directional Solidification ◽

Space Shuttle ◽

Solidification Process ◽

Space Experiment ◽

Infrared Detection ◽

Directionally Solidified ◽

Crystallographic Defects ◽

Semiconducting Alloys ◽

Uniform Composition ◽

Growth Experiments

The II-VI semiconducting alloys, such as mercury zinc telluride (MZT), have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities and crystallographic imperfections adversly affect the performance of MZT infrared detectors. One source of imperfections in MZT is gravity-induced convection during directional solidification. Crystal growth experiments conducted in space should minimize gravity-induced convection and thereby the density of related crystallographic defects. The limited amount of time available during Space Shuttle experiments and the need for a sample of uniform composition requires the elimination of the initial composition transient which occurs in directionally solidified alloys. One method of eluding this initial transient involves directionally solidifying a portion of the sample and then quenching the remainder prior to the space experiment. During the space experiment, the MZT sample is back-melted to exactly the point at which directional solidification was stopped on earth. The directional solidification process then continues.

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