A numerical and experimental study was carried out to investigate the transient response of a modified latent heat storage system. The proposed system was composed of phase change material (PCM) packed in the spaces between externally finned flow channel. Preliminary modeling for a system containing PCM with simple geometry and flow configuration was carried out either considering the natural convection or the effective thermal conductivity. The natural convection model was based on the solution of the vorticity and energy equations of both the PCM and the working fluid via a finite difference technique with Alternating Direction Implicit method (ADI). The conduction model was adopted based on an effective thermal conductivity (Keff) of the melted zone of the PCM. The results of the natural convection model were utilized in a parametric study to estimate Keff and new correlation was obtained. This correlation was permitted to a modified conduction model to predict the performance of enhanced storage systems with externally finned flow channels at different configurations. An experimental apparatus was designed and constructed to verify the numerical results. The influences of the working fluid mass flow rate, inlet fluid temperature, initial temperature of the PCM, flow channel pitch and fin configurations on the storage characteristics were investigated. It was found that the storage performance of the plain-channel systems is independent on Reynolds number beyond a value of 300. Also the enhancement in storage characteristics of the finned channel systems is strongly dependent on the fin pitch and the fin length while it does not depend on the fin thickness. New correlations were obtained for the melted volume ratio and the amount of the heat stored for the finned channel systems as functions of the different operating parameters