This study numerically investigates the thermal performance enhancement of a PCM-filled annular thermal energy storage (TES) system using rotational walls, considering both the solidification and melting processes. Various rotational configurations are explored. These configurations are separate rotation of the inner and outer walls, simultaneous rotation of both walls with different angular velocities, and rotations in both clockwise (CW) and counterclockwise (CCW) directions. The results show that the rotation of the walls induces forced convection which enhances heat transfer and accelerates PCM melting. The molten layers in proximity to the rotating walls show increased velocity causing improved flow effects. Higher rotational speeds result in stronger fluid flow and enhanced convection within the PCM enclosure, resulting in a larger volumetric fraction of PCM undergoing the melting process. Furthermore, the rotation of the walls promotes a more uniform distribution of heat and a homogeneous distribution of the molten PCM throughout the system. Simultaneously rotating both the inner and outer walls of the PCM enclosure reduces the total melting time which increases the overall efficiency of the TES system. Regarding the solidification process, the rotation of the PCM enclosure walls accelerates the typically slow solidification stage. Increasing the angular velocities causes a higher solidification rate because of enhanced mixing within the system. At the highest angular velocity, rotating the outer wall alone, reduces melting time by 49.06%, while rotating both walls (inner CW–outer CCW) leads to a maximum reduction of 62.15%. In solidification, outer wall rotation decreases the total solidification time by 55.91%, and rotating both walls (CW–CW) achieves up to 56.53% reduction. Overall, the findings of this study show the significant thermal performance enhancement achieved through the rotation of walls in PCM-filled annular TES systems.
