An improved transient calorimetric technique for measuring the total hemispherical emittance of nonconducting materials (emittance evaluation of glass sheets)

For measurements of the total hemispherical emittance epsilon(h) of nonconducting materials, a problem of the thermal gradient produced in a sample specimen arises. An improved transient calorimetric technique to reduce the thermal gradient is proposed in this study. Glass sheets (borosilicate), semi-transparent for radiation, are selected as the nonconducting test material. The epsilon(h) values of the glass sheets for various thicknesses are measured, and their results are presented as functions of thickness and temperature. The thermal gradients in the specimens are calculated by a three-dimensional analysis, and the corner effect due to them on the measured epsilon(h) is estimated. It is shown that the proposed technique is useful for measuring the emittance epsilon(h) of nonconducting materials.