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Published January 2009 | public
Book Section - Chapter

Modeling and Calibration of Fast-Response Coaxial Heat Flux Gages

Abstract

This research focuses on the modeling and calibration of fast response coaxial heat flux gages. Simulations of the heat conduction inside the gage using Gasp solver show, that the response is sensitive to geometry of the junction which sits on epoxy. The epoxy acts as an insulator creating a local overheating that increases with the junction aspect ratio and the step height between the inner and outer electrodes and decreases when epoxy is present next to the step. The increase of the overheating with the junction aspect ratio is due to the thermal insulation of the epoxy layer located under the junction used to electrically insulate the two electrodes of the thermocouple. When the junction protrudes significantly above the surface (about 10 microns), the heat transfer is enhanced from the larger surface area whereas, the lateral conduction around the epoxy layer decreases, which further contributes to the junction overheating. To assess those effects, a calibration method using a reflected shock in argon is developed and experiments are performed in the T5 free-piston shock tunnel which is used as a shock tube by replacing the nozzle throat insert with a closed end-wall insert. Five gages are simultaneously calibrated at a high heat flux for 30 microseconds. For microsecond time scales, it is found that the effective value of the thermal product, √pck, is approximately 30% lower than the average of chromel and constantan. The standard deviation of 10% among the five gages indicates that the gage-to-gage variation of the junction geometry is relatively small as the temperature is greatly sensitive to the geometry on microsecond time scales.

Additional Information

© 2009 by the American Institute of Aeronautics and Astronautics, Inc. Published online: 15 Jun 2012.

Additional details

Created:
August 20, 2023
Modified:
October 18, 2023