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Research Papers: Experimental Techniques

Convection Calibration of Schmidt–Boelter Heat Flux Gauges in Stagnation and Shear Air Flow

[+] Author and Article Information
A. Gifford, A. Hoffie, T. Diller, S. Huxtable

Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061

J. Heat Transfer 132(3), 031601 (Dec 22, 2009) (9 pages) doi:10.1115/1.3211866 History: Received December 01, 2008; Revised July 06, 2009; Published December 22, 2009; Online December 22, 2009

Experiments were performed to characterize the performance of Schmidt–Boelter heat flux gauges in stagnation and shear convective air flows. The gauges were of a standard design (25.4 mm and 38 mm in diameter), using a copper heat sink with water cooling channels around the active sensing element. A simple model of the gauges using an internal thermal resistance between the sensor surface and the heat sink is used to interpret the results. The model predicts a nonlinear dependence of the gauge sensitivity as a function of the heat transfer coefficient. Experimental calibration systems were developed to simultaneously measure the heat flux gauge response relative to a secondary standard under the same flow and thermal conditions. The measured gauge sensitivities in the stagnation flow matched the model, and were used to estimate the value of the internal thermal resistance for each of the four gauges tested. For shear flow, the effect of the varying gauge surface temperature on the boundary layer was included. The results matched the model with a constant factor of 15–25% lower effective heat transfer coefficient. When the gauge was water cooled, the effect of the internal thermal resistance of the gauge was markedly different for the two flow conditions. In the stagnation flow, the internal resistance further decreased the apparent gauge sensitivity. Conversely, in shear flow, the resistance was effectively offset by the cooler heat sink of the gauge, and the resulting sensitivities were nearly the same as, or larger than, for radiation.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Heat flux sensor with the three modes of energy transfer

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Figure 2

Heat flux gauge resistance network for convection

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Figure 3

Schematic diagram of the Schmidt–Boelter gauge

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Figure 4

Schematic of the convection calibration facility

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Figure 5

Stagnation calibration stand

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Figure 6

HFM mounting in a plate

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Figure 7

Shear stand nozzles

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Figure 8

Picture of the assembled shear stand

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Figure 9

Exit nozzle velocities from total pressure measurements

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Figure 10

Typical heat flux and temperature data for the shear stand

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Figure 11

Typical progression of the heat transfer coefficient for the shear stand

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Figure 12

Stagnation calibration sensitivities for SB 137861 in stagnation flow

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Figure 13

Calibration sensitivities for SB 137861 in shear flow

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Figure 14

Stagnation calibration sensitivities for SB 137861 in stagnation flow with water cooling

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Figure 15

Calibration sensitivities for SB 137861 in shear flow with water cooling

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