Development of High Temperature Phase-Change-Material Storages

Abstract

High-temperature PCM storage is a key component for storing latent heat. This is necessary for efficient energy storage in connection with the two-phase heat transfer fluid water/steam. Due to the low thermal conductivity of the nitrate salts used for high-temperature PCM storage, it is necessary to increase the heat transfer rate to meet the necessary power density demands for specific applications. A design for heat transfer enhancement using radially finned tubes has been developed by DLR and applied in a 700 kWh PCM storage demonstration module. The 700 kWh PCM storage has successfully been tested in a combined storage system for DSG. The operation of this PCM storage module for evaporating water in constant and sliding pressure mode was successfully demonstrated. Three different operation modes regarding flow for discharging the PCM storage have been tested successfully, showing potential for future cost reductions for the complete storage system. Here, either only the recirculation pump or even the complete circulation cycle including the steam drum could be eliminated. Good system operability of the systems was achieved. Furthermore, a new design based on extruded aluminum profiles, aiming at further cost reduction, has been developed by Brökelmann and DLR. Various fin designs have been analyzed with the finite element analysis software ANSYS® and optimized for a better temperature/heat distribution. The final design has been analyzed in a lab-scale PCM storage module. Test results of different operation parameters and thermo-mechanical examinations are shown and compared to theoretical analyses of the new design.