Assessing the impact of a novel hemispherical diffuser on a single-tank sensible thermal energy storage system

Abstract

The effects of an inlet inertial jet on the thermal blending of hot and cold heat transfer fluid (molten salt) for a single tank sensible thermal energy storage system are studied using numerical simulations. The simulations show the evolution of the initial stratified layer (thermocline) for a temperature difference of 300 K with a corresponding Atwood number (At) of 0.066. Three diffuser arrangements are investigated: a flat plate solid diffuser, a coaxial ring diffuser with a solid center, and a proposed hemispherical diffuser. The thermal stratifications are examined by a mathematical model named Ideal stratification index (ISI). It is observed that the buoyancy-driven mixing is minimum for the hemispherical diffuser, and the resulting thermocline is 6% better compared to alternative diffusers at 27 l/min. Additionally, the working of the proposed diffuser is demonstrated via experiments with a saline-freshwater combination. These results reveal that the single tank thermocline storage performance can be improved for higher charging/discharging rates using hemispherical diffusers.