Phase Change Process for Pure Substances Phase change at constant pressure Consider pure water in a sealed container with a floating top having no mass (atmosphere exerts constant pressure) Add heat until water just Keep adding heat as Keep adding heat until Initially at room conditions begins to“boil" liquid vaporizes” liquid is just gone” P=1 atm P=1atm P=1 atm P=1 atm .T=20C T=? vapor ,T=? vapor .T-? liquid" liquid 100℃ liquid 100℃ 100℃ Q Q (a)"compressed liquid" (b)“saturated liquid'” (c)“liquid-vapor mixture'” (d)“saturated vapor' Keep adding heat P=1 atm a unit mass(1kg) vapor ,T=300C 上游通大学 March 12,2019 (e)"superheated vapor" SHANGHAI JIAO TONG UNIVERSITYMarch 12, 2019 13 Phase Change Process for Pure Substances Phase change at constant pressure Consider pure water in a sealed container with a floating top having no mass (atmosphere exerts constant pressure) 100˚C 100˚C 100˚C a unit mass(1kg) atm