Abstract
An improved apparatus for measuring the spectral directional emissivity in the wavelength range between 1 µm and 20 µm at temperatures up to 2400 K is presented in this paper. As a heating unit an inductor is used to warm up the specimen, as well as the blackbody reference to the specified temperatures. The heating unit is placed in a double-walled vacuum vessel. A defined temperature, as well as a homogenous temperature distribution of the whole surrounding is ensured by a heat transfer fluid flowing through the gap of the double-walled vessel. Additionally, the surrounding is coated with a high-emitting paint and serves as blackbody-like surrounding to ensure defined boundary conditions. For measuring the spectral directional emissivity at different emission angles, a movable mirror is installed in front of the specimen, which can be adjusted by a rotatable arrangement guiding the emitted radiation into the attached FTIR-spectrometer. The setup of the emissivity measurement apparatus (EMMA) and the measurement procedure are introduced, and the derived measurement results are presented. For evaluating the apparatus, measurements were performed on different materials. The determined emissivities agree well with values published in literature within the derived relative uncertainties below 4% for most wavelengths.
Highlights
This includes the design of metrological infrastructure for performing traceable measurements of the temperature of fusion Tf, the thermal contact resistance Rc, the thermal diffusivity a, the specific heat capacity cp and the emissivity ε at high temperatures, which leads to the acronym Hi-TRACε or Hi-TRACE
This paper focuses on the improvement of an apparatus for measuring the emissivity
Test measurements have been performed on different specimens to evaluate the improved emissivity measurement apparatus (EMMA) in the whole temperature range
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A setup for determining the spectral directional emissivity at elevated temperatures has been developed at the Bavarian Center of Applied Energy Research (ZAE Bayern) [22] and extended previously at ZAE Bayern [23] Another setup is available at ZAE Bayern, namely the integrating sphere (IS) setup, which is an indirect radiometric method [24]. The emissivity measurement apparatus (EMMA) at ZAE Bayern has been significantly improved by applying new components for increasing the reliability and the temperature range up to 2400 K. These new components are mainly a novel vacuum vessel, an optimized beam path with movable mirrors and a new heating unit, which enables inductive heating for reaching very high temperatures. Selected results are presented and compared with available data from literature
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