Measurement of total hemispherical emittance of a nonconducting and semitransparent material by a transient calorimetric technique

An improved transient calorimetric technique was previously proposed for the measurement of the total hemispherical emittance, e h , of nonconducting materials and the results measured for Pyrex-glass sheets by the technique were reported. In this study, the e h values of a fused-silica glass sheet are measured by the same technique. A simple analytical way to evaluate the local total directional emittance, e*, of a glass sheet semitransparent to radiation is presented, and the e* values are computed on the surfaces of the specimen used. Further, values of the local total hemispherical emittance, e h *, on the specimen surfaces are obtained from e*. From the results for e* h , the edge effect of the specimen caused by the e* h distributions on the measured e h is clarified. The temperature distributions in the specimen are obtained by three-dimensional analysis, and then the edge effect caused by the distributions on e h is presented. It is found that the improved transient calorimetric technique is very suitable for measuring e h of nonconducting materials.