Computational fluid dynamics evaluation of the operating conditions for a volumetric receiver installed in a solar tower

A CFD (Computational Fluid Dynamics) model has been developed to study the wind influence and the effect of the return-air conditions on the efficiency of a volumetric receiver which was previously tested. The model validation obtained deviations lower than 5% for the air temperature at the absorber-cup outlet and an average deviation of 5.2% for the thermal efficiency evaluated in the receiver. In order to determine the influence of the wind conditions, different velocity magnitudes and incidence angles have been studied. The results showed that the outlet air temperature decreases with increasing wind magnitude and, at a fixed velocity, the increase of the incidence angle produces the decrease of the air outlet temperature. In both cases, the outlet air temperature decreases according to a second-degree polynomial function. Furthermore, the evaluation of the return-air influence considered its temperature and velocity as parameters. It was obtained that the greater the return-air temperature, the higher the air temperature at the outlet, and this temperature increases with lower return-air velocities. It was also observed that the return-air influence is greater when the wind velocity decreases, thus new receiver designs should avoid the direct incidence of the wind and should also consider an optimisation of the return-air conditions. (C) 2015 Elsevier Ltd. All rights reserved.