Charging and Discharging behaviour of Packed Bed Thermal Energy Storage using Dimpled Spherical Capsules with PCM

Packed bed thermal energy storage (TES) systems are widely employed in renewable energy applications due to their simplicity, scalability, and cost-effectiveness. This study investigates the transient thermal behaviour of a packed bed TES system utilizing dimpled spherical capsules filled with phase change material (PCM), emphasizing thermal response during charging versus discharging. The dimpled geometry is hypothesized to enhance heat transfer during both charging and discharging cycles by increasing surface area and promoting flow disturbance. Experimental trials are conducted to evaluate temperature evolution and energy storage rates. The key finding is that dimpled capsules offer improved thermal response and enhanced overall system performance. As compared to conventional smooth capsules, the dimpled spherical capsule offers maximum charging time reduction of 43.57% and discharging time reduction of 43.62% for the HTF operating at 1 L/min. The discharging to charging time ratio for PCM filled with dimpled spherical capsule are 1.84, 1.28 and 1.04 respectively for the heat transfer fluid operating at 1 L/min, 3 L/min and 5 L/min.