Prediction of thermocline zone development at the beginning of dynamic processes in single storage tanks with liquid media

Thermocline development in tanks with liquid storage media is strongly affected by both turbulence and fluid mixing, which mainly take place at the inlet. The occurrence of these phenomena leads to an increase of the thermocline zone thickness, which implies that less useful energy (exergy) can be extracted from the storage tank. Although this is an important issue, the majority of one-dimensional simulation models does not consider turbulence and mixing phenomena at the entrance and therefore, are not able to predict how the thermocline zone develops at the beginning of the dynamic processes. In this paper the effect of these phenomena in the initial formation of the thermocline has been evaluated by analyzing experimental data found in the literature for tanks with different inlet configurations. This effect has been quantified by means of an eddy function, which has been introduced as a correction to the fluid diffusivity. The dependence of this function with the Richardson number at tank inlet has been discussed for the thermocline tanks that have been analyzed. However, many questions still remain open since more systematic experiments with different inlet configurations and working conditions would be required.