ABSTRACT
This chapter presents an overview of the physical ideas relevant to phase-change processes. It introduces the precise mathematical formulation of the basic physical facts leading to the "Stefan Problem", the prototype of all phase-change models. The chapter discusses some of the complications and difficulties encountered in more realistic phase-change processes. The phase-transition region where solid and liquid coexist is called the interface. Its thickness may vary from a few Angstroms to a few centimeters, and its microstructure may be very complex, depending on several factors. Of course the complexity of the phase change process is only increased when other, sometimes extremely realistic physical phenomena are taken into account. Thus for example liquid paraffin wax easily dissolves air; on solidification the air is entrapped in the solid. In engineering applications one may have to accommodate such behavior, if possible, through suitable assumptions in a model not explicitly incorporating the phenomenon, or in the development of a more complete model.
