CFD model for the performance estimation of open volumetric receivers and comparison with experimental data

Abstract

Obtaining reliable information on the thermal performance of a receiver in a solar thermal power plant during the design phase is essential for optimisation purposes and for the determination of the economic performance of the entire power plant. In open volumetric receivers, where the heat transfer circuit is open to the environment, this task is particularly challenging due to the influence of convection phenomena on the air return ratio and thus the heat losses. These losses can only be estimated by means of CFD simulations, however, since the small scale absorber structure is several orders of magnitude smaller than the receiver itself, the required computational grid becomes too large to be economically viable. In this paper a modelling approach is presented, which for the first time allows the efficient simulation of the entire receiver including the flow in front of and around the receiver while at the same time considering internal heat transfer within the absorber. A set of boundary conditions has been developed for the absorber surface of open volumetric receivers in which the characteristic behaviour of the absorber is modelled without the need of detailed resolution of the absorber structure. The model has been validated against new measurements at the solar tower Jülich. Moreover, in comparison with literature data of air return ratio measurements a very good agreement was found. A characteristic map of the receiver efficiency has been compiled showing peak efficiencies of the open volumetric receiver of the solar tower Jülich of 70.9% at a hot air temperature of 650 °C and 75.4% at 450 °C. The model can now be used for the assessment of design concepts for commercial power plants.