A novel computational approach to combine the optical and thermal modelling of Linear Fresnel Collectors using the finite volume method

• Published in: Solar energy Vol. 116; pp. 407 - 427
• Main Authors: Moghimi, M.A., Craig, K.J., Meyer, J.P.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 01.06.2015; Pergamon Press Inc
• Subjects: CFD; Energy efficiency; False scattering and ray effect; Finite volume method; Fluid dynamics; Heat transfer; Linear Fresnel Collector; Monte Carlo simulation; Non-uniform solar heat flux; Optical properties; Scattering; SolTrace; SolTrace; CFD; False scattering and ray effect; Linear Fresnel Collector; Non-uniform solar heat flux
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2015.04.014

•A finite volume (FV) method combining optical and thermal modelling is presented.•The finite volume optical solution compares well with ray-tracing results.•An approach is developed that solves 2-D ray tracing and then 3-D heat transfer.•The sequential approach is validated by comparison with an expensive full model.•A single simulation environment is used for optical and thermal modelling of LFCs. A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) solver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against 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 source. 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 in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with 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 hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to maximise the performance of linear CSP reflector layout and receiver configurations.