Spectral Radiative Properties of Polydispersed SiO2Particle Beds

The focus of this work is on the measurement and analysis of the radiative properties of polycrystalline particle beds with various layer thicknesses. The particles are polydispersed with average diameters of 222, 150, and . The spectral, directional–hemispherical reflectance and transmittance of the particle bed are measured at wavelengths from 0.4 to using a monochromator, and the reflectance measurement is extended to using a Fourier-transform infrared spectrometer. Particles are closely packed between two transparent windows for measuring the radiative properties. In the visible and near-infrared region up to , the inverse adding–doubling method yields the effective absorption and scattering coefficients. The results suggest that short wavelength absorption needs to be included in modeling the behavior of particle beds due to multiple scattering. A discrete-scale Monte Carlo ray-tracing method is developed to model the radiative properties by assuming monodispersed spherical particles, and the simulated results compare well with measurements. The effective absorption and scattering coefficients of the particle beds obtained from the independent scattering theory are compared to those from the inverse method. The impact of dependent scattering on the packed beds is observed for smaller-sized particles.