1 Copyright © 2013 by ASME Proceedings of the ASME 2013 7 th International Conference on Energy Sustainability & 11 th Fuel Cell Science, Engineering and Technology Conference ESFuelCell2013 July 14-19, 2013, Minneapolis, Minnesota, USA ES-FuelCell2013-18149 THREE-DIMENSIONAL FLUID DYNAMICS AND RADIATIVE HEAT TRANSFER MODELING OF A SMALL PARTICLE SOLAR RECEIVER Pablo Fernández del Campo Combustion and Solar Energy Laboratory, San Diego State University, San Diego, CA, USA Fletcher Miller Combustion and Solar Energy Laboratory, San Diego State University, San Diego, CA, USA Adam Crocker Combustion and Solar Energy Laboratory, San Diego State University, San Diego, CA, USA ABSTRACT We present an investigation of the effects of the solar irradiation and mass flow conditions on the behavior of a Small Particle Solar Receiver employing our new, three-dimensional coupled fluid flow and radiative heat transfer model. This research expands on previous work conducted by our group and utilizes improved software with a set of new features that allows performing more flexible simulations and obtaining more accurate results. For the first time, it is possible not only to accurately predict the overall efficiency and the wall temperature distribution of the solar receiver, but also to determine the effect on the receiver of the window, the outlet tube, real solar irradiation from a heliostat field, non-cylindrical geometries and 3-D effects. This way, a much better understanding of the receiver’s capabilities is obtained. While the previous models were useful to observe simple trends, this new software is flexible and accurate enough to eventually act as a design and optimization tool for the actual receiver. The solution procedure relies on the coupling of the CFD package ANSYS Fluent to our in-house Monte Carlo Ray Trace (MCRT) software. On the one hand, ANSYS Fluent is utilized as the mass-, momentum- and energy-equation solver and requires the divergence of the radiative heat flux, which constitutes a source term of the energy equation. On the other hand, the MCRT software calculates the radiation heat transfer in the solar receiver and needs the temperature field to do so. By virtue of the coupled nature of the problem, both codes should provide feed-back to each other and iterate until convergence. The coupling between ANSYS Fluent and our in- house MCRT code is done via User-Defined Functions. After developing the mathematical model, setting up and validating the software, and optimizing the coupled solution procedure, the receiver has been simulated under fifteen different solar irradiation and mass flow rate cross combinations. Among other results, the behavior of the receiver at different times of the day and the optimum mass flow rate as a function of the solar thermal input are presented. On an average day, the thermal efficiency of the receiver is found to be over 89% and the outlet temperature over 1250 K at all times from 7:30 AM to 4:00 PM (Albuquerque, NM) by properly adapting the mass flow rate. The origin of the losses and how to improve the efficiency of the Small Particle Solar Receiver are discussed as well. INTRODUCTION Radiation in the form of light and heat from the sun is what we call solar energy and it is an outstanding source of renewable energy. It is free, renewable and only a minute percentage of the solar energy that reaches our planet is being used to produce electricity. Concentrated solar power is probably the most promising and economical way to utilize solar energy [1] and is being perfected continuously with the ultimate goal to produce cheap and non-polluting energy. In this context, a number of new technologies to efficiently convert solar energy into electricity are being investigated. In particular, while current commercial plants utilize Rankine steam cycles in the power block, there is a goal to develop higher-efficiency plants based on Brayton (or gas turbine) cycles. This technology possesses several advantages: (1) It requires less water to generate electricity; (2) it leads to higher thermodynamic efficiency (due to the higher temperatures required) [2]; and (3) the air is a non-problematic heat transfer fluid owing to its inert nature within the temperature range of interest. For that, new solar receivers are needed. One such receiver, first proposed by Hunt in 1979 [3], is the Small Particle Solar Receiver. This concept is based on employing carbon nanoparticles in an air stream to volumetrically absorb solar irradiation and drive a gas turbine at temperatures in excess of 1300 K, with the corresponding three advantages previously mentioned. Moreover, the Small