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Optical Engineering

Thermal Emissivity Of Diathermanous Materials
Author(s): R. H. Munis; S. J. Marshall
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Paper Abstract

Thermal (2.0 to 5.6 um) measurements of the normal emissivity EN of several diathermanous materials having slightly different refractive indices were made at 15.2 °C, 4.9 °C, and -5.6 °C. Calculations of the total hemispherical emissivity EH were made from EN and plotted against the optical depth PyaxX. A comparison of these data with a model proposed by R. Gardon [J. um. Ceram. Soc. 39(8), 278 (1956)] indicates that at near-ambient temperatures they agree very closely. This comparison presumes that the narrow range of refractive indices about n = 1.5 associated with these specimens would not preclude them from being treated as having a value of 1.5. It has been observed that EN > EH by 5% for both weakly and strongly absorbing materials. This is attributable to phase differences in the multiply reflected internal radiation attempting to exit the specimen throughout r steradians. Other radiation properties of the materials, i.e., diffuse transmittance TD, absorption coefficient Thx, and absorption index k, were calculated.

Paper Details

Date Published: 1 August 1985
PDF: 7 pages
Opt. Eng. 24(5) 245872 doi: 10.1117/12.7973591
Published in: Optical Engineering Volume 24, Issue 5
Show Author Affiliations
R. H. Munis, U.S. Army Cold Regions Research and Engineering Laboratory (United States)
S. J. Marshall, U.S. Army Cold Regions Research and Engineering Laboratory (United States)

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