Numerical simulation on the thermal performance enhancement of energy storage tank with phase change materials

The model of the energy storage tank based on multiple tubes with phase change material was established. The influence of the tube circle diameter and the inner annulus temperature on the heat storage performance of the tube bundle in the concentric circle was studied by numerical simulation. The results show that the increase of the tube circle diameter (Phi) can significantly improve the heat storage efficiency, and the increase in inner wall temperature (T-w) can make the heat storage time significantly shorter, but with the tube circle diameter (F) increases, the effect of T-w on shortening the heat storage time is gradually weakened. In addition, the dimensionless criterion equation of the liquid fraction function (f) at different tube circle diameters is presented too. Furthermore, based on the variation of the mean Nu with Fo, the heat transfer mechanism of the melting process of the PCM can be divided into four stages: (1) heat conduction dominates stage; (2) natural convection dominates stage; (3) natural convection begins to transform into heat conduction stage; and (4) heat conduction dominates again.