A numerical mathematical model has been developed to predict the thermal behavior of phase change material during thermal storage in a thermal tank. The model is based upon energy conservation equations and includes fusion of the phase change material. The thermal behavior of the phase change material during charging and discharging have been studied numerically, and analyzed under different conditions. Comparisons were made against experimental data for validation purposes of the predictive model. The model fairly predicted experimental data obtained at various inlet conditions of the phase change material.