This paper examined a one-equation approach to thermal energy storage in a packed bed of alumina with air as heat transfer fluid. This modeling approach assumes thermal equilibrium between the fluid and solid phases, which is valid here based on the high heat capacity and thermal conductivity of the solid compared to the fluid. The model solves the axial and radial temperature profiles in the packed bed, insulation, and vessel. The model matches experimental data well for two flow-rate conditions. For accuracy, temperature-dependent thermophysical properties of the air and alumina must be used. This effect is particularly important at the high temperatures expected in applications like CSP (e.g., 700C). Those using this approach should be careful to ensure that thermal equilibrium is valid and the Biot number remains less than 0.1 to avoid intra-particle conduction effects.
Acknowledgments
The authors would like to acknowledge Dr. Pablo Bueno and Dr. Hitesh Bindra for guidance and training in the collection of the experimental data. This work was originally supported by the Department of Energy grant DE-FC36-08GO18151. Special thanks are also given to Jorge Pulido for his work in setting up the experiment.