A novel computational approach to the combine optical and thermal modelling of a linear fresnel collector receiver

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

A computational approach is presented that uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) solver ANSYS Fluent to perform both the ray tracing required to quantify the optical performance of a line-concentration Linear Fresnel Collector (LFC) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. It is shown that the Discrete Ordinates method can provide an accurate solution of the Radiative Transfer Equation (RTE) if the shortcomings of its solution are addressed appropriately in the FV CFD solver. This approach is evaluated for a 2-D sample test case that includes a 2-D LFC optical domain of which the results are compared to those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric resource. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach, the 2-D:3-D approach is compared to results of a fully integrated, but expensive, 3-D optical and thermal model. It is shown that the less expensive model provides similar results and that it provides the benefit of working in one simulation environment, i.e., ANSYS Workbench, where additionally optimization studies can be performed in future work.