Thermal Emissivity Of Diathermanous Materials

R. H. Munis; S. J. Marshall

doi:10.1117/12.7973591

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.

Citation Download Citation

R. H. Munis, R. H. Munis, S. J. Marshall, S. J. Marshall, } "Thermal Emissivity Of Diathermanous Materials," Optical Engineering 24(5), 245872 (1 August 1985). https://doi.org/10.1117/12.7973591 . Submission:

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