In recent years, concentrating solar thermal power has emerged as the most promising technology for utility scale solar electricity generation. Central receiver systems, which are one method of concentrated solar power, use a field of sun-tracking mirrors called heliostats to focus light on a receiver. Existing receivers used in these systems have temperature and flux limitations, which prevent the use of advanced power cycles and reduces plant efficiencies compared to fossil fuel power plants. The development of air-cooled receivers and small particle receivers in particular are summarized herein. A new type of receiver has been proposed, which makes use of small carbon particles and volumetric absorption in a gas-particle mixture to heat air directly. This thesis builds on previous modeling work done in FORTRAN on the San Diego State University small particle receiver project, expanding the Monte Carlo ray-trace model to include the computation fluid dynamics capabilities of ANSYS FLUENT with the use of several user-defined functions. The input flux is modified to more closely match that provided by a real heliostat field, and the geometry is changed to more accurately approximate a real receiver. The updated model is benchmarked against existing analytical solutions where possible, and compared to the results of the previous model. The new model is run for a variety of gas mass-flow rates, inlet power levels, and power distributions with a baseline target input power of 5 MW. Outlet gas temperatures predicted by the model ranged from 1300 K to 1550 K, and receiver thermal efficiencies ranged from 80% to 91% depending on operating conditions. The highest efficiencies predicted are with the highest mass-flow rate tested of 6 kg/s.