A Test of Analytical Expressions for the Thermal Emissivity of Shallow Cylindrical Cavities

On Kirchhoff's law and its generalized application to absorption and emission by cavities

“…The different values of flux absorbed which correspond to the many diffe re nt possible source positions with respe ct to the spacecraft can be evaluated quickly to any desired degree of accuracy by using modern computer techniques. This calculational proce dure has actually been employed for certain cases of illumination in shallow cylindrical cavities and good agreement with experimental values was found [7].…”

“…Here x is the distance from the mouth of the cavity along the walls; r is th e radial di stan ce from the center of the cav ity base. The apparent local spectral e mittan ce distribution Ea(l\., x) and Ea(l\., r) were taken from reference [7], figure 4. For convenience, it is assumed that the cavity wall material is gray (its spectral emittance does not vary with wavelength).…”

Procedures for precise determination of thermal radiation properties, November 1964 to October 1965

“…The measured value of this ratio, E 2 , is given by The effects of translucency can be summarized as follows: (1) the reflectance of a band of width r at the top of the cavity will be reduced, (2) the emittance of a band of width r at the top of the cavity will be reduced, (3) the emittance of a circular band of width r surrounding the cavity will be reduced, and (4) the apparent emittance of the circular band of width r surrounding the cavity will be increased due to flux incident on the cavity wall that is transmitted by the specimen and emitted in the circular band. Effects (3) and (4) …”

“…(1) continued development of the laser-source integrating sphere reflectometer, (2) an error analysis of the shallow cavity technique for measuring normal spectral emittance, and (3) a study of the feasibility of preparing emittance standards for use at temperatures above 1400°K (about 2000°F). …”

“…Specific objectives for the current contract year included (1) continued development of the lasersource integrating sphere reflectometer for measuring reflectance of specimens at high temperature, (2) …”