## Description

The Combustion and Solar Energy Laboratory (C&SEL) at San Diego State University is developing a Small Particle Heat Exchange Receiver (SPHER) to absorb and transfer heat from concentrated solar radiation to a working fluid for a gas turbine. The SPHER is to be used with a Concentrated Solar Power (CSP) system where a heliostat field highly concentrates solar radiation on the optical aperture of the SPHER. A unique carbon nanoparticle gas mixture within the cavity of the SPHER volumetrically absorbs the solar radiation. This research focuses on comparing a Computational Fluid Dynamics (CFD) model using the ANSYS FLUENT Discrete Ordinates (DO) Model and a program developed by the C&SEL which uses a Monte Carlo Ray Trace (MCRT) method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry. Previous research at the C&SEL has shown successful implementation of the MCRT method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry. An alternative method for calculating the Radiative Transport Equations (RTE) being considered uses a FORTRAN program, developed by the C&SEL, with the ANSYS FLUENT DO model for calculating the RTE. The methodology used for determining the correct CFD mesh, radiative boundary conditions, optimal number of DO theta and phi discretization, as well as the optical properties of the participating fluid are presented in this thesis. For a gray semi-diffuse radiative input with absorption the DO and MCRT method calculate a mean outlet temperature and receiver efficiency of 1320 K, 75.1%, 1406 K, and 85.2% respectively. Adding a scattering to the gas-particle mixture, the DO and MCRT method calculate a decrease in the mean outlet temperature of 1286 K, 69.0%, 1383 K, and 80.3% respectively. Using a non-gray radiative input with a 4-band absorption coefficient and linear anisotropic scattering coefficient the DO method calculates a mean outlet temperature of 1328 K and receiver efficiency of 72.0%. The MCRT method calculates a mean outlet temperature of 1410 K and receiver efficiency of 81.7%.