Sublimation

When the initial pressure of the ice at 0°F is 0.0505 psia, heat transfer to the ice first outcomes in a rise in temperature to 20°F. At this point, though, the ice passes directly from the solid phase to the vapor phase in the process termed as sublimation. The sublimation is a special word used for situations in which the transition among the solid phase and the vapor phase takes place directly, without passing via the liquid phase. Further heat transfer would outcome in superheating the vapor.