Total Normal and Total Hemispherical Emittance of Polished Metals

The objective of this research is to determine the ratio of the total hemispherical to total normal emittance for various classes of surfaces in order to find correlation factors between the total normal emittance usually measured and the total hemispherical emittance which is of importance in heat transfer problems. Measurements were made on polished Pt between 800 and 1500 deg K. The total hemispherical emittance was obtained from the electrical power dissipation in an electrically heated strip suspended in a vacuum of better than 0.0001 mm Hg and its absolute temperature measured by a thermocouple. The total normal emittance was determined with a radiation thermopile. The ratio of total hemispherical to total normal emittance was calculated directly from the angular distribution of radiation obtained by revolving the detector about an axis through the ribbon. The total emittance of polished platinum was given to within + or - 5%. Data were taken on the spectral emittance at 0.65 microns and on the electrical resistivity. Observations were made on the various measured quantities with time.