Experimental study and analytical modeling on the thermocline hot water storage tank with radial plate-type diffuser

The thermocline storage tank (TCST) is a cost-effective device that can be integrated into district heating networks for peak shaving. The formation and variation in the thermocline thickness with time in the TCST are key parameters to evaluate the performance of the TCST. Therefore, the TCST with a radial plate-type diffuser is studied experimentally and theoretically in this study. The stratification of the storage tank is divided into the formation and developmental stages, and a modified 1D analytical model is developed and compared with the experimental data. The correction coefficient ε is defined to quantify the enhancement in the thermal diffusion of the thermocline. This parameter can improve the accuracy of the 1D analytical model. The average percentage error of the analytical model is reduced from 48.7% to 18.5%. The quantitative relationship between ε and the tank Reynolds number is obtained. For the formation stage of the thermocline, the correlation equation between the thickness of the initial thermocline and the inlet Reynolds and inlet Froude numbers is determined experimentally. Then, with ε and the thickness of the initial thermocline, the algebraic relationship of the thickness of the thermocline with time is investigated. The prediction error of the 1D analytical model for the variation in the thermocline thickness with time is 13.9%.