Total hemispherical emittance of Irtran 2, 4, and 6 at low temperatures.

Measurements of total hemispherical emittance of selected Irtran filters are reported for the temperature range 45 degrees K to 312 degrees K. Values obtained for 1-mm thick specimens are 0.38, 0.23, and 0.15 for Irtran 2, 4, and 6, respectively, at 312 degrees K; 0.49 for Irtran 2 at 75 degrees K and 0.35 and 0.43 for Irtran 4 and 6 at 45 degrees K. All three specimens have emittance maxima of approximately 0.5 at intermediate temperatures. Thicker specimens have somewhat greater values. Total normal emissivity calculated from spectral normal emissivity data for Irtran 2 and 4 agree well with the experimental results. Specific heat measurements of the Irtran specimens for the same temperature range are also reported.