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Proceedings Paper

Flow-field velocity measurements for nonisothermal systems
Author(s): Edward J. Johnson Jr.; Paul V. Hyer; Paul W. Culotta; Ivan O. Clark
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Paper Abstract

An effort to characterize the fluid dynamics of nonisothermal, chemically reactive flows of gaseous mixtures inside fused silica chemical vapor deposition (CVD) reactor vessels is underway at the NASA Langley Research Center. This effort is in support of microgravity investigations of fluid dynamics and multiphase flows. A quantitative understanding of the basic fluid dynamics associated with CVD is necessary to achieve improvements in layer thickness and compositional uniformity, in abruptness of alloy interfaces, and in growth efficiency. To perform this research, a three-component laser velocimetry (LV) system has been adapted specifically for quantitative determination of the mixed convective flows found in chambers used for crystal growth and film formation by CVD. A discussion of the advantages and disadvantages of this instrument compared to flow visualization and particle image velocimetry (PIV) techniques is presented. A fundamental limitation on the application of all particle-based velocimetry techniques in nonisothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias arises from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a horizontal research CVD reactor are presented which indicate that current models for the effects of this thermophoretic force are not adequate to predict the thermophoretic bias in arbitrary flow configurations. Thermal effects on the flow field inside the research reactor were investigated by comparing data obtained from the reactor both at room temperature and heated to growth temperature by radio frequency (rf) induction. Heating of the susceptor was found to increase the gas velocities parallel to the face of a slanted susceptor by up to a factor of five and to result in as much as a factor of eight increase in velocity components directed toward the hot surface.

Paper Details

Date Published: 1 December 1991
PDF: 12 pages
Proc. SPIE 1557, Crystal Growth in Space and Related Optical Diagnostics, (1 December 1991); doi: 10.1117/12.49595
Show Author Affiliations
Edward J. Johnson Jr., Lockheed Engineering and Sciences Co. (United States)
Paul V. Hyer, Lockheed Engineering and Sciences Co. (United States)
Paul W. Culotta, Lockheed Engineering and Sciences Co. (United States)
Ivan O. Clark, NASA/Langley Research Ctr. (United States)

Published in SPIE Proceedings Vol. 1557:
Crystal Growth in Space and Related Optical Diagnostics
James D. Trolinger; Ravindra B. Lal, Editor(s)

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