Robert Flesch

Reducing the convective losses of cavity receivers

Convective losses reduce the efficiency of cavity receivers used in solar power towers especially under windy conditions. Therefore, measures should be taken to reduce these losses. In this paper two different measures are analyzed: an air curtain and a partial window which covers one third of the aperture opening. The cavity without modifications and the usage of a partial window were analyzed in a cryogenic wind tunnel at −173°C. The cryogenic environment allows transforming the results from the small model cavity to a large scale receiver with Gr≈3.9·1010. The cavity with the two modifications in the wind tunnel environment was analyzed with a CFD model as well. By comparing the numerical and experimental results the model was validated. Both modifications are capable of reducing the convection losses. In the best case a reduction of about 50 % was achieved.

Dynamic modeling of molten salt power towers

A detailed understanding of the transient behavior of a receiver using molten salt as heat transfer fluid is of great importance for an efficient and safe operation. To analyze the transient operation a dynamic model for the flow in the receiver is currently under development, which will be capable to analyze the one-phase flow during normal operation and the two-phase flow during filling and draining. The model can be coupled to raytracing simulation in order to use a realistic flux density distribution as input for the model. In the paper the modelling approach for the receiver model is described shortly and validation results are discussed. This includes a detailed discussion of the heat transfer during the filling procedure, where an interesting phenomenon was discovered. Finally, the results for a parameter variation of the filling procedure and the simulation results for the impact of certain cloud events on the operation of the receiver are presented.

Dynamic Modelling of Molten Salt Central Receiver Systems

Molten salt central receiver (MSCR) systems are a very promising option for the large-scale production of electricity from solar radiation. A central receiver system consists of a field of thousands of mirrors which reflect the sunlight to the top of a tower, at which the receiver is located. The receiver is built of tubes where molten salt is flowing through as the heat transfer fluid. The salt is heated up due to the concentrated solar radiation. The hot salt can be easily stored in large unpressurized tanks driving a convectional steam plant afterwards. The efficiency and the easy storage option have made the MSCR system to the predominant concentrating solar technology in the recent years.