Recently, thermal energy storage (TES) includes technologies for collecting and storing energy for later use in domestic and industry by using Phase Change Materials (PCMs) which is a main topic for many researchers. In this experimental and numerical study, melting process and thermal behavior due to a U-shaped heat source embedded in the PCM is investigated which has been simulated in COMSOL-3D Multiphysics. The three-dimensional governing equation is solved for the fluid flow and heat transfer behavior. Two different cases are analyzed in this study. In the first case, the experimental results of a rectangular cavity filled with PCM, and a Ushaped heating source embedded in it is validated with a numerical model. PCM is used that has melting point temperature 32 °C, and flow of water at temperature 39 °C for six hours period through the U-shaped tube to intensify the PCM`s temperature. PCM melts and absorbs latent heat as energy which is analyzed horizontally and vertically. PCMs temperature increased uniformly with increasing of time inside the cavity. The melting rate was high around the heating source than the far distances of heating source. After six hours, 100% PCM was melted around the U-shaped tube, however, far from the U-shaped tube was not significantly melted in both experimental study and numerical model. The numerical results are in good agreement with the experimental data with a small number of relative error in all cases. In the second case, PCM and Bentonite are used in four different models in the same rectangular cavity, then hot-water and, cold-water flowing through the U-shaped tube, and the numerical results were validated for all models. It was observed that, when Bentonite is used, the heat transfer rate was higher compare to the case when PCM is used for anywhere in the cavity. The reason is that, Bentonite has higher thermal conductivity and temperature gradient than the PCM. So, Bentonite was more sensitive for heat transfer whenever used in heating or cooling. It is clear from this study that PCM and Bentonite can be a good media for storing thermal energy for later use such as room heating, space heating, industrial and commercial uses. PCM has a great possibility to it, because of its low initial and maintenance cost, and its availability.