All over the world, with the increase in population and industries, the amount of energy demand is increasing day by day, and due to the lack of non-renewable energy sources and the permanent unavailability of renewable sources, the discussion of energy storage has become very important among engineers. One of the ways of energy storage is using phase change materials. Based on this, in this thesis, energy storage in a helical coil heat exchanger has been investigated experimentally. The fluid inside the coil is water and a special type of paraffin is used as energy storage in the shell. The effect of shell geometry and fluid flow on the charging ( melting ) and discharging ( freezing ) performance of this storage system has been studied. The studied geometries for the shell are: cubic, spherical, and trapezoidal, and the volume of all of them is considered to be the same and 0.9 liters.The results are presented for different points inside the phase change material, the fluid output from the coil, and the charging and discharging time in different modes. Exergy analysis was also done for the obtained results. For comparison, numerical simulations have been performed for spherical shell geometry.The results for a flow rate of 6 liters per minute showed that using a trapezoidal shell instead of cubic and spherical shells reduces the time of the melting process by 22.73 % and 10.53 %, respectively. In the freezing process, using a spherical shell instead of a cubic and trapezoidal shell reduces the processing time by 13.33 % and 21.21 %, respectively. Also, the time to perform the entire process of melting and freezing in this flow in the spherical shell has decreased by 13.54 % and 1.19 %, respectively, compared to the cubic and trapezoidal shells. The energy efficiency in the spherical shell has increased by 3.2 % and 34.8 %, respectively, compared to the cubic and spherical shells. Also, the exergy efficiency in the spherical shell increases by 1.6 % and 10.3 %, res