Temperature-dependent spectral emittance of bauxite and silica particle beds

ABSTRACT

Bauxite and silica particles are candidate materials for solar thermal energy storage at high temperatures. The temperature-dependent emittance of packed beds with bauxite and silica particles was measured using a newly upgraded emissometer at wavelengths 2 μm ≤ λ ≤ 16 μm and temperatures up to ~730 K. The room-temperature emittance was obtained from the measured directional-hemispherical reflectance. A fused silica disc was used to test the emissometer by comparing the measured spectral emittance with the calculated emittance from a fitted Lorentz oscillator model. For the polycrystalline silica particles and the fused silica disc, the measured emittance increases with temperature in the mid-infrared region. The underlying mechanism is interpreted as the temperature-dependent damping coefficient in the Lorentz oscillator model. Two types of bauxite particles with different compositions and sizes were investigated. For λ > 10 μm, the measured emittance at elevated temperatures is higher than that at room temperature. In the region 2 μm < λ < 6 μm, the temperature dependence varies for different types of particles. The total emittance of bauxite particle beds was calculated by spectral integration using Planck’s distribution at the prescribed temperature. The calculated total emittance is between 0.89 and 0.96, but it does not change monotonically with temperature.

KEYWORDS:

• Emittance
• high temperature
• particle bed
• radiative properties
• radiation

Nomenclature

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Acknowledgments

This work was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office Award Number EE0008372. C.Y. was supported by the National Science Foundation (CBET-2029892). The views expressed herein do not necessarily represent the views of the U.S. Department of Energy, National Science Foundation, or the United States Government. The author would also like to thank Shomik Verma and Malavika V. Bagepalli for their help in the experiments.

Disclosure statement

No potential conflict of interest was identified by the authors.

Data availability

The data that support the findings of this study are available upon request from the corresponding author with reasonable request.

Additional information

Funding

This work was supported by the National Science Foundation [CBET-2029892]; Office of Energy Efficiency and Renewable Energy [EE0008372].