Numerical study of packed bed thermal energy storage with natural sandstone rock as a filler material

Packed bed thermal energy storage system is one of the promising solutions to store energy from the renewable power generation plants in the form of thermal energy. The selection of storage material is an important factor for the efficient functioning of the packed bed storage system. In this study, sandstone has been chosen as a storage material because of its good thermophysical properties such as high thermal conductivity, specific heat capacity, and density required for the energy storage in a packed bed, economic viability, and abundantly availability. The aim of the paper is to investigate the thermohydraulic characteristics of the packed bed storage with sandstone rocks as filler material and air as heat transfer fluid. A three-dimensional, dynamic model of a cylindrical packed bed thermal energy storage is developed in Ansys fluent. Transient simulations of the charging phase are carried out with a uniform void fraction of 0.39 and an airflow rate of 0.15?kg/s. Results from the model are compared with the experimental data with a reasonable agreement. The validated model is further used to assess the impact of temperature-dependent thermophysical properties of filler material on the dynamics of the sandstone packed bed energy storage. Results show that there is a significant difference in the performance characteristics when the model uses temperature-dependent properties. The sandstone rock bed with temperature-dependent properties takes a longer charging time, shows a relatively narrow thermocline region and higher pressure drop compared to the case with constant properties.