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A review on experience feedback and numerical modeling of packed-bed thermal energy storage systems

An analysis, with experimental results, for the transient response of a packed bed thermal storage unit is presented. The analysis is in two-spatial dimensions and considers the influence of both axial and radial thermal dispersion for an arbitrary time and radial variation in the inlet fluid temperature. Both charging and recovery modes are included. Spatial variations in void fraction are found to have significant effect on the dynamic response of both fluid and solid temperatures. The influence of radial velocity variations, wall heat capacity and wall thermal losses are considered. The analysis is valid for fluids of various Prandtl numbers. Experimental measurements of temperature distributions in a randomly packed bed of uniform spheres, with air as the working fluid, compare favorably with the analytical results over a broad range of Reynolds numbers. Results are presented for full-sized rock beds which indicate pronounced effects of void distribution in such systems.

Transient response of a packed bed for thermal energy storage

The detailed study of latent packed bed thermal energy storage (TES) system has been a great topic of interest in the literature. Experimental measurements have been conducted to analyze the performance of these systems, however, the complex transient nature of latent TES makes necessary the use of numerical models for detailed study and evaluation of key design parameters, which lead to a numerous scientific contributions in the field. Different and diverse numerical models have been developed, which can be mainly divided into single phase models, Schumman's model, concentric dispersion model, and continuous solid phase model. This paper provides an extensive comprehensive revision of the different numerical models, highlighting the key aspects of each one as well as the main findings in the field. Furthermore, the performance of the different methodologies are discussed and compared. The most important empirical correlations used in the different models in order to take into account physics, such as natural convection inside the spheres or effective thermal conductivity of heat transfer fluid, are also given.

T.R. Galloway

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