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Laser velocimetry measurements in non-isothermal CVD systemsResearchers at the NASA Langley Research Center are applying laser velocimetry (LV) techniques to characterize the fluid dynamics of non-isothermal flows inside fused silica chambers designed for chemical vapor deposition (CVD). Experimental issues involved in the application of LV techniques to this task include thermophoretic effects on the LV seed particles, seeding the hazardous gases, index of refraction gradients in the flow field and surrounding media, optical access, relatively low flow velocities, and analysis and presentation of sparse data. An overview of the practical difficulties these issues represent to the use of laser velocimetry instrumentation for CVD applications is given. A fundamental limitation on the application of LV techniques in non-isothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias results from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a research CVD reactor are presented which indicate that current models for the interaction of forces such as Stokes drag, inertia, gravity, and thermophoresis are not adequate to predict thermophoretic effects on particle-based velocimetry measurements in arbitrary flow configurations.
Document ID
19930039819
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Johnson, E. J.
(NASA Langley Research Center Hampton, VA, United States)
Hyer, P. V.
(NASA Langley Research Center Hampton, VA, United States)
Culotta, P. W.
(Lockheed Engineering and Sciences Co. Hampton, VA, United States)
Clark, I. O.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1991
Publication Information
Publication: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 2 (A93-23776 08-35)
Publisher: American Society of Mechanical Engineers
Subject Category
Instrumentation And Photography
Accession Number
93A23816
Distribution Limits
Public
Copyright
Other

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