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 0.0094m 3 /s, 0.013m 3 /s, and 0.019m 3 /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-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 m 3 /s airflow rate. Keywords: thermal analysis, concrete-bed, charging, discharging, storage efficiency. # I. I eat transfer in concrete beds is used to describe a variety of phenomena, namely: (1) the convective heat transfer from the walls of the concrete bed to the fluid; (2) the convective heat transfer from the particles to the fluid flowing through the bed, which can be referred to as the fluid-particle mode; (3) the conduction heat transfer from the walls of the bed to the particles constituting the bed; (4) the conduction heat transfer between the individual particles in the bed; this can also be referred to as the particle-particle mode; (5) radiant heat transfer; and (6) heat transfer by mixing of the fluid (Adeyanju and Manohar 2009). These modes are described schematically in Figure 1.0. The fourth mode, namely the conduction between the particles, can be further subdivided into the axial and radial directions. Moreover, at high temperatures heat transfer by radiation will also be an important mode. In many industrial applications, it is found that two or more of the modes cited above take place simultaneously. For example, the conduction between the particles may be affected by the convection between the particles and the fluid. This interaction among the different modes is one of the main reasons for the difficulty in correlating the total heat transfer and analyzing the experimental data in this field (Balakrishnan and Pei 1974). This study analyzed theoretically the temperature distribution and energy storage ability of a simultaneous charging and discharging concrete bed Storage System. # II. # Review of Literature The first work on heat transfer in packed beds was published by Anzelius et al. (1926), although Schumann (1929) is usually the first reference cited in most literature (Adeyanju and Manohar 2009). Each of them made a number of simplifying assumptions and solved the heat transfer equations for an incompressible fluids passing uniformly through a bed of solid particles with perfect conductivity. The derived heat transfer equations were: ( ) ( ) ( ) , 0 - , 0 - 1 - - s s Y Z n n Y Z n n s s T T e Y M yz e Z M T T ? ? ? = ? = ? (1) ( ) ( ) ( ) ( ) - ,0 , 0 - 1- - f s Y Z n n Y Z n n f s T T e Y M yz e Z M yz T T ? ? ? ? ? ? ? =? = ? ? ? ? ? (2) Where T is the temperature (of fluid and solid) and Y and Z are dimensionless quantities. The solutions of these equations were presented in graphical form, called Schumann curves. Thus to evaluate volumetric coefficients of heat transfer using these curves, it was only necessary to measure exit air temperature and the bed temperature. These curves could be used to evaluate the heat transfer coefficients for a given packed bed undergoing heat exchange with a fluid provided the following conditions which were the simplifying assumptions made by Schumann were satisfied: 1. The solid particles were so small or have such a high thermal conductivity that no temperature gradients exist within the solid particles. This means that the solids offer a negligible resistance to heat transfer. 2. The resistance to heat transfer by conduction in the fluid was also negligible. 3. The rate of heat transfer from fluid to solid or vice versa at any point in the bed was directly proportional to the average temperature differential between them at that point. 4. The densities of solid and fluid and other transport properties were independent of temperature. Upholding the above conditions, Furnas (1930) extended the Schumann curves to wider coverage temperatures. He also postulated an empirical relation for the evaluation of the heat transfer coefficient as shown in equation (3): Where, h v is the volumetric heat transfer coefficient. B is a constant dependent on the bed material, G is the mass velocity of the fluid, T is the average air temperature, d p is the particle diameter and ? is the porosity. Saunders and Ford (1940) used dimensional analysis to derive correlations to calculate heat transfer coefficient. The work was, however, limited to spheres and cannot directly be applied to other geometries of solid particles. Kays and London (1964) presented another correlation for evaluating heat transfer coefficient between gases and randomly packed solid spheres. Using the Colburn j-factor, the correlation was given as: This was evaluated for 8mm