A new experimental apparatus for measurement of spectral emissivity of opaque materials using a reflector as the dummy light source

A new experimental apparatus has been developed, which can be used to accurately measure the spectral emissivity of opaque materials using a reflector as the dummy light source. The experimental apparatus is mainly composed of the optical detection system, heating system, temperature-controlling system, angle-adjusting system and signal-controlling and data-computing system. The optical system works at 1.5 μm and the bandwidth is 20 nm. The sample can be heated up to about 1200 K by the sample heater. The temperature of sample surface is measured by the two highly accurate platinum–rhodium thermocouples and is controlled by means of a microcomputer-controlled proportional–integral–derivative device. The temperature-controlling error is within 2 K over the experimental range from 700 to 1200 K. A reflector is used as the dummy light source to realize the single-wavelength measurements of spectral emissivity. The present apparatus can be used to perform the measurements of spectral emissivity as a function of temperatures and emission angles. The spectral emissivity of several opaque materials has been measured by the apparatus. As an example, the spectral emissivity results of polished aluminum sheet over the temperature range from 788 to 1028 K have been reported here. The analytic dependence between the spectral emissivity and temperature has been determined. The temperature determined by the two thermocouples is employed to assess the accuracy of spectral emissivity measured here. The comparison between the temperatures measured by the thermocouples and those calculated by the emissivity obtained here demonstrates that the results measured by the apparatus achieve much high accuracy and that the proposed measurement technique is reliable.