EXPERIMENT FOR MODELING HIGH-TEMPERATURE ROCK BED STORAGE

High temperature thermal storage in rock beds using air as a heat transfer medium was repeatedly proposed for large solar power plants. Subsequently, a mathematical model describing the thermal behavior of such a storage system was developed. This one-phase dynamic model solves analytically the one-dimensional linear nonhomogeneous boundary-value problem for the heat transfer between air and particles, leading to a computer code called PACKBEDA. Recently, this program has been improved and modified in order to include the temperature dependent thermophysical properties of air (density, viscosity, and thermal conductivity), as well as the heat losses through the insulated walls. Moreover, the program keeps track of the amount of pressure drop across the solid bed. To validate this model, an experimental store called ARIANE was built. Measurements of the transient behavior of the rock bed during the charging process show a fairly well stratified temperature distribution. Due to the somewhat unfavorable shape of the storage vessel with its high surface-to-volume ratio, the heat losses through the wall are considerable. These features are well reproduced by the modified computer program PACKBEDA which seems to be a reliable and useful tool for the analysis of large scale air/rock bed storage systems.