Flow patterns of external solar receivers

Abstract

A The design of the flow paths in solar external-receivers with molten salt as heat transfer fluid is critical to increase the Solar Power Tower (SPT) availability and for a reliable receiver operation. The parameters that affect mostly the start-up and shut-down of the receiver are the Direct Normal Irradiance (DNI) and the sun elevation angle. Furthermore, the feed-pump system requirements and the limiting turbulent Reynolds number also affect the number of operational hours to assure safe receiver operation. Under nominal conditions of operation the most critical factors are the maximum film temperature and the thermal stresses. In this study, the receiver performance has been analysed during its annual operation. Different flow pattern configurations have been simulated including single or multiple flow paths with or without crossovers. The selection of the optimal configuration has been based on increasing the receiver availability and the global efficiency of the SPT. In the light of the results, during start-up and shut-down the total solar flux intercepted by both flow paths should be approximately the same. However, close to midday to maintain high levels of thermal efficiency a good distribution of the solar flux (peak flux close to the northern panels) is more important. The most efficient and reliable flow path configuration is a receiver with two modes of operation: a crossover just before the midpoint of the path when the solar flux is low and North South asymmetric or no crossover when the DNI is high and the peak flux is still asymmetric.