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Research Papers: Experimental Techniques

Transient Calorimetric Measurement Method for Total Hemispherical Emissivity

[+] Author and Article Information
Tairan Fu

Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering,  Tsinghua University, Beijing 100084, P. R. China;  Beijing Key Laboratory of CO2 Utilization and Reduction Technology, Beijing 100084, P. R. Chinatrfu@mail.tsinghua.edu.cn

Peng Tan1

Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Thermal Engineering,  Tsinghua University, Beijing 100084, P. R. China

1

Corresponding author.

J. Heat Transfer 134(11), 111601 (Sep 24, 2012) (7 pages) doi:10.1115/1.4006896 History: Received May 25, 2011; Revised May 15, 2012; Published September 24, 2012; Online September 24, 2012

The transient calorimetric technique was used to measure the total hemispherical emissivity of conductive materials. The emissivity was measured in a small central region of a thin strip heated electrically in a vacuum chamber. The axial heat transfer along the sample and the heat losses from the wires were considered in the transient heat transfer calculations. An appropriate time interval for the hot sample cooling rate is needed to improve the emissivity solution accuracy. Two ways were used to analyze the data, based on the known specific heat and the assumed functions of the emissivity and the specific heat. Comparisons with steady-state data showed that their results are very similar with a maximum difference of only 13% (944 K). Therefore, the transient method based on the function assumption is a good choice for measurements when there are inaccurate or insufficient specific heat data at the desired temperatures. Since ferromagnetic materials have Curie points at higher temperatures, this study also investigated the applicability of the transient calorimetric technique for high temperature emissivity measurements. For higher temperatures above the Curie point, the steady-state method is more accurate than the transient method. These analyses provide a comprehensive understanding of the transient method for measuring the total hemispherical emissivity.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sample temperature during cooling for the #45 steel sample

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Figure 2

Cooling rate for various time intervals, (a) Δτ = 0.5 s, (b) Δτ = 1 s, (c) Δτ = 2 s, and (d) Δτ = 4 s

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Figure 3

Ratio of the heat conduction along the sample to the total heat loss

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Figure 4

Total hemispherical emissivity variations

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Figure 5

Calculated specific heat of #45 steel

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Figure 6

Comparison between the measured temperature and the estimated temperature

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Figure 7

Specific heat of #45 steel [18]

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Figure 8

Sample temperature during cooling for the #45 steel sample B

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Figure 9

Cooling rate (Δτ = 2 s) for the #45 steel sample B

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Figure 10

Predicted emissivities using different methods

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