The emissivity is a radiative property of materials that describes the capability of a surface to emit electromagnetic radiation. Accurate emissivity data are required for many high-temperature technological applications, but literature values are often widely scattered, and acquisition of reliable data at working temperatures is of particular importance. In this contribution, we will present the latest update of the HAIRL emissometer of the University of the Basque Country UPV/EHU, as well as the method used for the accurate measurement of infrared emissivity as a function of temperature. The HAIRL is a unique instrument that allows performing spectral directional emissivity measurements in the mid-to-near infrared range (0.83 - 25 µm). It is equipped with a vacuum chamber (10-5 hPa) that permits measuring under different atmospheric conditions in a wide range of temperatures (300-1273 K). The integration of spectral and directional results allows the determination of the total hemispherical emissivity, a parameter of great utility in heat transfer simulations.
In recent years, significant improvements have been made to this infrared emissivity measurement system, including a complete revision of the uncertainty calculation and the use of a Monte Carlo method to propagate the uncertainty [1]. A new control system has been designed to declaratively define the conditions of the experiment to be carried out, which can be remotely controlled and monitored through web applications. Current advances in reproducibility and temperature control to improve the measurement system, and allow measuring semitransparent materials, will be considered. Some illustrative examples of selective absorbers used in concentrated solar power, as well as alloys for fusion reactors and advanced Ti-base aeronautical alloys, will also be presented.