Radiative Transport Models for Solar Thermal Receiver/Reactors

Modeling the behavior of solar-driven chemical reactors requires detailed knowledge of the absorbed solar flux throughout the calculation domain. Radiative transport models, which determine the radiative intensity field and absorbed solar flux. are discussed in this paper with special attention given to particular needs for the application of solar thermal receiver/reactors. The geometry ofinterest is an axisymmetric cylinder with a specified intensity field at one end, diffuse reflection at boundaries, and containing a participating medium. Participating media are of interest because receiver/reactors are expected to have one or more zones containing small particles or monoliths acting as absorbers or catalyst supports, either of which will absorb, emit, and scatter radiation. Ageneral discussion of modeling techniques is given, followed by a more complete discussion of three models--the two-flux, discrete ordinate, and the Monte Carlo methods. The methods are compared with published benchmark solutions for simplified geometries-the infinite cylinder and plane slab-and for geometries more closely related to receiver/reactors. Conclusions are drawn regarding theapplicability of the techniques to general receiver/reactor models considering accuracy, ease of implementation, ease of interfacing with solution techniques for the other conservation equations, and numerical efficiency.