A CFD-supported dynamic system-level model of a sodium-cooled billboard-type receiver for central tower CSP applications

This work focusses on the dynamic modeling of a sodium-cooled billboard-type receiver, as adopted in the reference plant of this study, the Jemalong Solar Thermal Station, in Australia. A detailed system-level thermal-fluid-dynamic model is developed in the OpenModelica framework, with the aim to predict the receiver behavior during transients, as well as its performance upon reaching steady-state conditions. The model solves the conjugate heat transfer problem relating conduction in the receiver pipes to the internal flow of sodium. The convective losses from the irradiated face of the receiver, due to the external flow of air, are calculated using empirical correlation available in literature for flat-plates and then carefully evaluated using 3D Computational Fluid Dynamics (CFD), which allows taking into account the actual geometry of the receiver. The CFD results, considering different wind speeds and highlighting the cavity-like effects of the receiver geometry under consideration, are first compared with those obtained from empirical correlations available in the literature for vertical plates in the case of uniform temperature distribution on the absorber pipes, showing significant differences. Then an iterative coupling procedure with the system-level model of the same receiver is proposed, which facilitates handling of the more realistic case of a non-uniform temperature distribution. Finally, we present and discuss the successful benchmark in a simple case of the system-level model against another model from the literature, its preliminary validation against experimental data, and first applications to a fast start-up/passing cloud/shut-down transient and to a whole-day simulation with controls.