Spectral Radiative Properties of Ceramic Particles for Concentrated Solar Thermal Energy Storage Applications
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Spectral Radiative Properties of Ceramic Particles for Concentrated Solar Thermal Energy Storage Applications Chuyang Chen1 · Chiyu Yang1 · Devesh Ranjan1 · Peter G. Loutzenhiser1 · Zhuomin M. Zhang1 Received: 11 July 2020 / Accepted: 17 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This work investigates the spectral radiative properties of ceramic particles using a monochromator and a Fourier-transform infrared spectrometer (FTIR) with integrating spheres at wavelengths from 0.38 μm to 15 μm. Particles are encased between two transparent windows to obtain the directional-hemispherical reflectance of the particle bed. Two types of commercially available particles with three different sizes are examined. Integration over the solar spectrum reveals that the solar absorptance of the particle beds is between 0.940 and 0.957. The total emittance at 1000 K is also estimated by assuming the spectral emittance is independent of temperature. The optical constants of particles are modeled with effective medium approaches, considering the optical properties of individual constituent materials. The absorptance of the particle is estimated using the effective optical constants and compared with that of the particle bed from the measurement. This work facilitates the characterization of radiative properties of particles with a windowed method and provides a modeling scheme for approximating the radiative properties of composite ceramic materials. Keywords Absorptance · Ceramic particles · Effective medium approaches · Packed particle bed · Radiative properties List of Symbols a𝜆 Absorption coefficient, m−1 d Thickness, m E Emissive power, W·m−2 E𝜆 Spectral emissive power, W·m−2·μm−1 G𝜆 Spectral irradiance, W·m−2·μm−1 * Zhuomin M. Zhang [email protected] 1
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
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International Journal of Thermophysics
(2020) 41:152
n Refractive index R Directional-hemispherical reflectance T Directional-hemispherical transmittance Greek Symbols α Absorptance ε Emittance 𝜀̃ Complex dielectric function (relative electric permittivity) κ Extinction coefficient or imaginary part of the refractive index λ Wavelength, μm ρ Reflectivity at the surface σ The Stefan–Boltzmann constant, 5.670 × 10−8 W·m−2·K−4 τ Internal transmissivity ϕ Volume fraction Subscripts b Blackbody E or O Extraordinary or ordinary component eff Effective h Host j Index for individual constituent p,s,w Particle bed, sample (particle bed with window), and window λ Spectral
1 Introduction Solar thermal energy storage (TES) materials have drawn increased attention due to their wide range of applications for converting sunlight into electricity in concentrated solar power (CSP) applications [1–3]. Heliostat fields are often employed in large-scale systems to redirect and focus sunlight to central receivers, where solar energy is absorbed and stored via late
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