Transient Behavior of a Rock-Bed Thermal Storage System Subjected to Variable Inlet Air Temperatures: Analysis and Experimentation

An analytical solution to the transient thermal behavior of a rock-bed thermal storage system subjected to varying air inlet temperature is presented. The solution is obtained in terms of infinite double series which are based on Schumann’s solution, derived for a step change in air inlet temperature. In the present study, bed and fluid temperatures in response to arbitrary fluid inlet temperatures are calculated by means of Duhamel’s theorem. Results of this study were verified experimentally and compared to a numerical solution. Agreement in both these cases was very good. Pressure drop data were compared to values predicted by two previously published correlations. These correlations were found to underpredict the measured data by factors in the range 1.5–5. Reasons for this discrepancy are mainly due to the differences in the type and particularly the shapes of rocks used in the different studies.