The heat storage tank is an indispensable component in a solar thermal utilization system. To improve the efficiency of a solar water heating system

phase change material Ba(OH)2?8H2O was added to a heat storage tank. The thermal properties of the heat storage tank were then studied through experiments when the initial water temperature was 80 ℃ and the inlet temperature was 5 ℃. Results showed that the heat storage of the water tank increased from 18.81 to 19.07 MJ when adding the phase change material. With the increase in the inlet volume flow rate

the MIX number of the water tank initially decreased and then increased

whereas the effective heat release efficiency first increased and then decreased. The maximum efficiency of 92.2% occurred at a flow rate of 3 L/min. The addition of the phase change material could increase the heat release efficiency and heat stratification characteristics of the heat storage tank

and the closer the position of phase change material is to the inlet

the better the improvement is.