Abstract

This study analyzed theoretically the temperature distribution and energy storage ability of a simultaneous charging and discharging concrete bed Storage System. This was achieved by first modeled a single spherical shaped concrete which was used to represent a sequence of points along the axis of the beds. A one dimensional finite difference formulation was used in modeling the single spherical shaped concrete material, where heat conduction to neighboring spherical concrete was ignored. Using this assumption reduced the spherical shaped concrete model to that of an isolated sphere in cross flow, where the total surface area of the sphere was exposed to convection. The thermal properties of the materials within the bed accounted for temperature dependence. Comparisons were made between charging and discharging mode of the storage system for air flow rates of 0.0094m3/s, 0.013m3/s, and 0.019m3/s. It was discovered that the difference of the temperature response between the charging and fluid to solid heat transfer process at the initial period of the packed bed was large and the heat recovered by the cool air flowing inside the copper tube was fairly high (larger inlet#x2013;outlet temperature difference compared with the later period indicates larger heat recovery). The energy storage efficiency was also analyzed and it was discovered that spherical shaped concrete of 0.11m diameter has the highest storage efficiency of 60.5% at 0.013 m3/s airflow rate.