SUMMARY

The thermal radiative properties and light scattering mechanism in particle beds are important for solar energy conversion by particulate medias. The purpose of this proposal is to investigate the intrinsic radiative properties of bauxite and silica particles as solar thermal energy storage materials and develop understanding of light scattering mechanism within their relevant particle beds. The radiative properties of bauxite particles are studied by measuring and modeling their spectral absorptance. Using the effective medium approach, the optical constants are modeled and used to calculate the theoretical absorptance. A high temperature emissometry is developed to measure the temperature dependent emittance of bauxite and silica particle beds. Semitransparent particle beds of silica particles are measured for the particle size dependent reflectance. A direct discrete scale Monte Carlo Ray Tracing (MCRT) simulation is developed to help understand the experimental results, and further investigate the effect of relative bed thickness and the particle packing density (volume ratio). Optimization over these parameters leads to beds of dedicated performance of maximum absorptance and reflectance, providing design guidance to devices utilizing particulate medias. Polydisperse particles of different types enhance radiative properties by altering the scattering mechanism. A bi-particle system of bauxite and silica particles is proposed to enhance radiation heat transfer. A MCRT simulation will be used to predict the performance of the bed and will be validated by experiments. The effect of dependent scattering on beds radiative properties is closely related to the particle concentration (number density). Equivalent beds with different concentrations and same density are proposed for investigation. Simulation results from MCRT, which considers dependent scattering, will be compared with a continuum scale simulation of radiative transfer equation (RTE) under the independent scattering assumption.