|The warm-side thermal chamber used for thermography
experiments has been outfitted with a servo-motor-controlled traversing system for
moving probes in three dimensions. Air velocity and air temperature probes collect data
near the surface of test specimens. An electronic dial gauge maps the geometry of surfaces
being tested. These measurements complement infrared surface temperature measurements by
aiding the analysis of localized natural convection film coefficients. Comparing measured
surface temperatures to simulated surface temperatures has led us to conclude that
variations in local convection heat transfer rates are significant.
|A computer controlled traversing system first maps the specimen surface geometry. Then the traverse is programmed to move probes in an array of positions that follow the surface to within 0.5 mm. The distribution of air temperatures very near the specimen is measured with 0.25 mm resolution.|
|Thermal boundary layer probe for
air temperatures near surfaces
|Fluid boundary layer probe for measuring air velocity near surfaces.|
This diagram represents the velocity profile (top curve) and the air temperature profile (lower curve) next to a vertical surface that is colder than the surrounding still air. Boundary layer theory suggests that within the inner boundary layer (y< ym) the temperaure profile is linear. In our experiments we measure about 8 temperature points within this region and fit a line through them. From the slope of the line and the surface temperature we can calucalate a local convective heat transfer coefficient.
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