Experimental setup for direct measurements of spectral directional emissivity from 0° to 80° angles at temperatures as low as 40 °C

Abstract

In this work, a direct method is developed for measuring the spectral directional emissivity of optically thick materials for temperatures ranging between 40 °C and 450 °C at angles from 0° to ∼ 80°. The direct method consists in measuring and comparing thermal radiation emitted from a sample to that of a blackbody reference source. Emphasis is placed on the importance of accurate calibration when performing measurements at low temperature (<50 °C) and on the assessment of uncertainty, estimated between 2 and 20% in the best and worst configuration respectively. The sample is fixed on a heater mounted on a rotation stage allowing directional measurements. Thermal radiation is collected by an optical setup and sent to a Fourier-transform infrared spectrometer (FTIR) performing spectral measurements in the 2–25 μm range using a room-temperature DTGS detector. Sample, blackbody source and optics are placed inside a black-coated enclosure purged with dry air and equipped with temperature sensors for estimating angle-dependent ambient radiation incident on the sample. As examples to illustrate the capabilities of the setup, directional spectral measurements are performed from normal to 80° on both a SiO2 and an aluminum sample at 100 °C.