Numerical Analysis of Thermal Stratification in Large Horizontal Thermal Energy Storage Tanks

Abstract

In order to enhance the performance of a large horizontal thermal energy storage, a numerical model was generated and validated using measurements obtained from Drake Landing Solar Community (DLSC). A total of nine different baffle configurations were tested in order to enhance the thermal stratification. The designs were tested for a total of six different cases of charging, discharging and simultaneous charging and discharging in an attempt to better identify key features that mix the tank under realistic conditions. Characterization of the tank performance was done by monitoring the tank outlet temperature and computing Huhn's efficiency Second Law characterization index).

Results show that the current tanks at DLSC experience excessive mixing due to plume entrainment that occurs during the spreading of the inlet jet. The introduction of a baffle into the middle of the tank was found to have no impact on the level of stratification. In addition, most designs tested have a relatively high level of stratification during charging, discharging and simultaneous charging and discharging, but fail to sustain the level of stratification when a positive buoyant jet is introduced.

It was demonstrated that the inlets and outlets should be moved to the top and bottom of the tank to eliminate stagnant fluid that is not easily discharged. Horizontal baffles are effective in allowing the inlet jet to spread horizontally but not vertically, thus reducing the mixing. Alternatively, a simple solution would be to increase the size of the inlet, which has a comparable performance to the best baffle configurations.