Apparatus for investigating total hemispherical emissivity
J. H. Cairns
An apparatus is described for measuring the total hemispherical emissivity of highly polished metals and alloys over the temperature range 100 to 900°C. The apparatus consists essentially of a highly polished, hollow, cylindrical sample supported within an evacuated enclosure of only slightly larger dimensions. Provision is made for raising the temperature of the sample above that of the enclosure by means of an internal heater contained within the hollow sample. Emissivity values are obtained by observing the rate of loss of heat from the sample after switching off the heater, and substituting this observed value in a specially derived radiation equation. An accuracy of better than ±8% and a reproducibility of ±5% are claimed for the emissivity values. Experimental data for titanium are included as an example. The apparatus is also capable of direct measurement of specific heat over the same temperature range to an accuracy of ±2%.
