In this paper the results of a numerical investigation of the melting and solidification process of sodium nitrate, which is used as phase change material, will be presented. For the heat transfer to the sodium nitrate different finned tube designs, namely helical-, transversal- and longitudinal finned tubes, are used. The numerical results of the melting and solidification process for the different design cases will be compared. The numerical analysis of the melting process has shown that apart from the first period of the charging process natural convection is the dominant heat transfer mechanism. The numerical analysis of the melting process has also shown that for a fast melting process heat exchanger tubes should be designed in such a way that an unrestricted natural convection is guaranteed.
The numerical investigation for the solidification process has shown that the dominant heat transfer mechanism is heat conduction. The investigation has also shown that the solidification front grows more uniformly from the tube surface to the outer shell compared to the melting front. Therefore no significant differences between the different tube designs are detected concerning the solidification process.