ABSTRACT Experimental and numerical study of the transient performance of a packed bed thermal storage system was carried out. Experiments were carried out to measure the transient temperature distributions inside a cylindrical packed bed with air as a working fluid. The packing was composed of rock grains of irregular sizes ranging between 14 and 20 mm. The bed container was constructed from a PVC cylinder with 1 m overall height and 0.15 m inside diameter. Measurements of the bed temperature were conducted at different axial and radial positions and at different operating parameters. The present problem was modeled using two time-dependent coupled partial differential equations of the energy conservation of air and solid phases. The fluid energy equation was transformed by finite difference approximation and solved by Alternating Direction Implicit scheme (ADI) while the solid energy equation was solved using fully explicit scheme. The solution provides predictions for the dimensionless temperature distributions for both fluid and solid phases within the packed bed in the radial as well as in the axial direction for both charging and recovery modes at different operating parameters. The influence of aspect ratio, the flowing air velocity, the inlet air temperature, bed size and bed thermal capacity are also investigated. Three correlations were obtained from the present results for the bed charging duration, effectiveness, and the storage efficiency as functions of the different operating and design parameters.