Thermal performance of a packed bed thermocline thermal energy storage system according to the design parameters

The influence of design parameters on the thermal performance of a packed bed thermocline thermal energy storage (TES) system was analyzed. Both one-dimensional (1D) and two-dimensional (2D) in-house codes were developed in MATLAB environment. The diameter of solid filler, height of storage tank, and fluid velocity were varied. The thermal performance of the system, such as discharging time, thermocline thickness, and energy efficiency was calculated. As the diameter of the solid filler and fluid velocity increased, and the height of the storage tank decreased, the discharging time decreased. As the diameter of the solid filler and the height of storage tank increased, the thermocline generally became thicker. The thermocline thickness according to the fluid velocity showed non-monotonic behavior: initially increasing and then decreasing, since it affected heat transfer coefficient, fluid-solid contact time and discharging time, which affected thermocline expansion. The 2D model exhibited higher energy efficiency than the 1D model, due to the consideration of the additional wall heating to the fluid, resulting in extended discharging time except for very low flow velocities.