Session: 05-02 Metrology in CSP

Paper Number: 117099

117099 - Methods for Quantitative Temperature-Dependent Optical Metrology 

The next generation (Gen3) of concentrated solar power technologies (CSP) will operate at higher temperatures (> 600 °C) to take advantage of increased power cycle efficiencies. At high temperatures, the contribution of thermal radiation to the overall heat transfer increases. To predict and measure radiative heat fluxes requires optical properties, including emittance, reflectance and absorptance. While these properties are essential to optimize the thermal performance, spectral and temperature-dependent experimental data for optical properties are generally scarce, and even if present are subject to large scatter in the data sets. These limitations are further exacerbated by the dependence of measured properties on extraneous factors including diffuse/specular surface finish, thermal history, and reducing/oxidizing conditions in an environment. To fill this gap, this project focuses on developing spectroscopic methods to measure reflectance and emittance for temperatures up to 1000 °C and as a function of environmental conditions. To add credibility to the measurement techniques developed and the data sets generated, Fourier transform infrared (FTIR) spectrometer measurements are made by a team of researchers from two independent research labs. Through a direct comparison of results and comprehensive uncertainty quantification, we have developed strategies and operational procedures to obtain quantitative reflectance and emittance data as a function of temperature and to additionally minimize random and systematics errors. Select materials and morphologies relevant to Gen3 CSP technologies are considered and tested – ceramic powders (alumina, silica, composites), alumina tiles, metal foils (Stainless steel, Incoloy), and coatings (Pyromark). Reflectance and/or emittance data have been obtained for a temperature range of 25 – 1000 °C. Preliminary results show promising comparisons between the two groups for room temperature diffuse reflectance measurements for metallic samples. The team has developed new strategies to mitigate the effects of thermal emission  in reflectance measurements, at especially high temperatures (> 500 °C). At high temperatures, results reveal significant sensitivity of reflectance and emittance measurements to: (a) detectors used in the FTIR, (b) uncertainties in temperature quantification of the sample measured, (c) oxygen impurities in the testing environment and (d) thermal history of the samples tested. All data obtained from this project is hosted in a shareable, digital database to enable broader adoption and use of cross-verified optical property measurements for various high-temperature and CSP materials.

Presenting Author: Rohini Bala Chandran University of Michigan

Presenting Author Biography: Assistant Professor at UM, Mechanical Engineering