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RESEARCH PAPERS: Radiative Properties

Experimental and Computational Characterization of High Heat Fluxes During Transient Blackbody Calibrations

[+] Author and Article Information
Amanie N. Abdelmessih

Department of Mechanical Engineering, Saint Martin’s University, 5300 Pacific Avenue, S.E. Lacey, WA 98503-1297abdelmessih@stmartin.edu

Thomas J. Horn

National Aeronautics and Space Administration, Dryden Flight Research Center, P.O. Box 273, MS 48202A Edwards, CA 93523;thomas.j.horn@nasa.gov

J. Heat Transfer 132(2), 023304 (Dec 01, 2009) (13 pages) doi:10.1115/1.4000187 History: Received October 30, 2008; Revised April 07, 2009; Published December 01, 2009; Online December 01, 2009

High heat fluxes are encountered in numerous applications, such as on the surfaces of hypersonic vehicles in flight, in fires, and within engines. The calibration of heat flux gauges may be performed in a dual cavity cylindrical blackbody. Insertion of instruments into the cavity disturbs the thermal equilibrium resulting in a transient calibration environment. To characterize the transient heat fluxes, experiments were performed on a dual cavity cylindrical blackbody at nominal temperatures varying from 800°C to 1900°C in increments of 100°C. The pre-insertion, steady state, axial temperature profile is compared experimentally and numerically. Detailed transient thermal models have been developed to simulate the heat flux calibration process at two extreme fluxes: the high flux is 1MW/m2 and the relatively low is 70kW/m2. Based on experiments and numerical analysis, the optimum heat flux sensor insertion location as measured from the center partition was determined. The effect of convection (natural and forced) in the blackbody cavity during the insertion is calculated and found to be less than 2% at high temperatures but reaches much higher values at relatively lower temperatures. The transient models show the effect of inserting a heat flux gauge at room temperature on the thermal equilibrium of the blackbody at 1800°C and 800°C nominal temperatures. Also, heat flux sensor outputs are derived from computed sensor temperature distributions and compared with experimental results. The numerical heat flux agreed with the experimental results to within 5%, which indicates that the numerical models captured the transient thermal physics during the calibration. Based on numerical models and all experimental runs the heat transfer mechanisms are explained.

Copyright © 2010 by U.S. Government
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Figures

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Figure 1

Schematic of blackbody calibration system with location of instruments

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Figure 2

Axisymmetric mesh of the left cavity of the blackbody assembly and heat flux gauge

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Figure 3

Axial temperature distribution at a nominal temperature of 1800°C for an insulated blackbody configuration

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Figure 4

Axial temperature distribution at a nominal temperature of 800°C for an uninsulated blackbody configuration

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Figure 5

Axial heat flux measurements during insertion in the blackbody at 1800°C nominal temperature

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Figure 6

Variation in heat flux with axial distance inside the insulated blackbody cavity for temperatures varying between 1100°C to 1900°C

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Figure 7

Variation in heat flux with axial distance inside the uninsulated blackbody cavity for temperatures varying between 800°C to 1100°C

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Figure 8

Comparison of experimental numerical temperatures for the blackbody cavities at nominal 800°C steady state

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Figure 9

Comparison of experimental numerical temperatures for the blackbody cavities at nominal 1800°C steady state

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Figure 10

Effect of inserting the heat flux gauge in one side of the cavity on the power input for a blackbody at a nominal 1800°C

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Figure 11

Effect of inserting the heat flux gauge in one cavity on the control pyrometer in the other cavity

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Figure 12

Transient axial blackbody temperatures, due to insertion of the heat flux gauge in the same cavity (left) at 800°C

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Figure 13

Transient axial blackbody temperatures, due to insertion of the heat flux gauge in the same cavity (left) at 1800°C

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Figure 14

Transient axial temperatures due to insertion of a heat flux gauge in the opposite cavity of a blackbody at 800°C

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Figure 15

Transient axial temperatures due to insertion of a heat flux gauge in the opposite cavity of a blackbody at 1800°C

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Figure 16

Effect of inserting the heat flux gauge on the partition at 1800°C

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Figure 17

Effect of inserting the heat flux gauge on the partition facing the opposite cavity at 1800°C

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Figure 18

Effect of inserting the heat flux gauge in the blackbody cavity on the sensing surface of the gauge at 1800°C

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Figure 19

Effect of inserting the heat flux gauge in the blackbody cavity on the sensing surface of the gauge at 800°C

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