Radiative Heat Transfer of Coatings on a Cryogenic Surface

An analytical model for the radiative characteristics of coatings formed on a cryogenic surface is presented. In creating a realistic mathematical model, six different sets of boundary conditions are employed in order to determine which most closely approximates the actual experimental results. The medium is considered to be absorbing and scattering; due to the cryogenic temperatures involved, emission is justifiably neglected. The scattering is considered as isotropic. To determine the best analytical model, the theoretical results are compared to experimental data in order to provide a test of the validity of the radiative transfer theory upon which the analytical predictions are based. Then using a combination of experimental results and the chosen analytical model, the monochromatic absorption and scattering coefficients for H2O and CO2 cryodeposits are simultaneously determined in the visible wavelength region. The results are demonstrated in the form of hemispherical-directional reflectance and intensity profiles within the medium. Also bidirectional reflectance distributions are presented and compared with experimental data. Prepared in cooperation with ARO, Inc., Tullahoma, TN. Rept. no. ARO0VKF-TR-71-66.