21 January 1985 Thermal (2-5.6 µm) Emittance Of Diathermanous Materials As A Function Of Optical Depth, Critical Angle And Temperature
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Abstract
Thermal (2.0 μ - 5.6 μm) measurements of the normal emittance (EN) of several diathermanous materials were made at 15.2°C, 4.9°C and -5.6°C. Calculations of the total hemis-pherical emittance (EH) were made from EN and plotted against the optical depth (YΔλx). A comparison of these data with a model proposed by Gardon indicates that at near-ambient temperatures they agree very closely. 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 π steradians. Other radiation properties of the materials, i.e. diffuse transmittance (TD), absorption coefficient yΔx, and absorption index k were calculated.
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R. H. Munis, S. J. Marshall, "Thermal (2-5.6 µm) Emittance Of Diathermanous Materials As A Function Of Optical Depth, Critical Angle And Temperature", Proc. SPIE 0510, Infrared Technology X, (21 January 1985); doi: 10.1117/12.945025; https://doi.org/10.1117/12.945025
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