Experimental and numerical investigation of the melting process of solar salt in a spherical capsule

Solar salt is commonly employed as phase change material in various industrial applications, particularly in latent heat-based thermal storage systems such as packed beds in solar thermal power technologies. Here, a series of experimental and numerical studies are conducted of the melting process of a binary nitrate salt inside a spherical capsule under a wide range of large Stefan numbers, specifically ranging from 0.56 to 1.12. For a deep understanding of the melting behavior inside the sphere and its heat transfer characteristics under different constant wall temperatures and sphere sizes, the visualized high-temperature phase change experiment along with a 2D axisymmetric numerical model are presented. To confirm modelling reliability, the numerical model well-realized the sinking phenomena visualized in the experiment with a suitable mushy-zone parameter value of 6*10(8) kg/(m(3)<middle dot>s). Subsequently, the temperature field, flow field, melting front, total transfer rate and melting time are explored. Further, a detailed parametric investigation is applied, including the effects of dimensionless parameters such as Gr, Ste on the melting process. And finally, the dimensionless correlation is succeeded to be proposed for unconstrained melting process with 0.56 <= Ste <= 1.12 and 1.80E+04 <= Gr <= 2.02E+05.