ABSTRACT
This chapter examines phase change heat transfer in the solidification and melting processes. It focuses on heterogeneous nucleation as the onset of solidification processes. Solidification and melting occur in many engineering systems such as materials processing, phase change materials, and molten salts for thermal energy storage of solar thermal or advanced nuclear power plants. Two methods are commonly used in the analysis of solid–liquid phase change problems—either an interface tracking method or a mixture formulation. Various types of microstructures are formed during solidification processes. Allotropy refers to the existence of two or more molecular or crystal structures within a solidified material. Interstitial diffusion refers to the migration of atoms through microscopic openings in the lattice structure of a solid. Nucleation occurs when the probability of atoms arranging themselves on a crystal lattice is high enough to form a solid crystal from the liquid. Homogeneous nucleation refers to solidification of liquid initiated by undercooling alone.
