The refrigerant evaporates the seawater and is cooled as thermal energy is absorbed by the refrigerant from the seawater. Boiling takes place in the sea water because of the high vacuum maintained by the exhauster. As a result, ice crystallisation takes place. The seawater first enter the tank where crystallisation in the form of an pure ice is formed.
Evaporation can operate over a widely varying temperature with the wide range of the vapour-pressure relation.
Both may use water or other refrigerants as the refrigerating fluid in either direct or indirect heat-transfer relation. Water is not very suitable as the refrigerant for mechanical compression systems because of its low vapour pressure and large vapour volume at the freezing point. Ammonia has been scraped from the metal freezing surface and melted.