Lesson 5 CHANGE OF PHASE

1. Lesson 5CHANGE OF PHASE • DISTINGUISH between intensive and extensive properties. • DEFINE the following terms: • Saturation • Subcooled liquid • Superheated vapor • Critical Point • Triple Point • Vapor pressure curve • Quality • Moisture Content • DESCRIBE the processes of sublimation, vaporization, condensation, and fusion.

2. Classification of Properties • Intensive Properties - independent of the amount of mass present • Pressure • Temperature • Density • Extensive Properties - a function of the amount of mass present. • Volume • Mass • An extensive property may be made intensive by dividing the particular property by the total mass

3. Piston – Cylinder Arrangement

4. Classification of Properties (cont.) • Saturation - A condition in which a mixture of vapor and liquid can exist together at a given temperature and pressure. • Saturation Temperature (Boiling Point) - The temperature at which vaporization (boiling) starts to occur for a given pressure. • Saturation Pressure – The pressure at which vaporization (boiling) starts to occur for a given temperature • Subcooled Liquid – Liquid with temperature that is lower than the saturation temperature for the existing pressure. • Quality (x) - The ratio of the mass of the vapor to the total mass of both vapor and liquid when a substance exists as part liquid and part vapor at saturation conditions

5. Vapor Pressure Curve

6. T-V Diagram Showing the Saturation Region

7. Classification of Properties (cont.) • Moisture Content - the fraction of the total mass of a mixture that is in the liquid phase • Saturated and Superheated Vapors - a vapor at a temperature above saturation temperature for its pressure • Constant Pressure Heat Addition

8. Constant Pressure Heat Addition

9. Classification of Properties (cont.) • Critical Point – Point where there is no constant-temperature vaporization process. Rather, point N is a point of inflection, with the slope being zero. Saturated-liquid and saturated-vapor states are identical • Fusion - The process of melting • Sublimation - Transition between the solid phase and the vapor phase occurs directly, without passing through the liquid phase (dry ice). • Triple Point - The state in which all three phases may be present in equilibrium

10. Pressure – Temperature Diagram

11. Summary Classification of Properties • Intensive properties are independent of mass (temperature, pressure, or any specific property) • Extensive properties are a function of the mass of the system (mass, volume)

12. Summary (continued) Terms • Saturation - combination of temperature and pressure at which a mixture of vapor and liquid can exist at equilibrium • Subcooled liquid - a liquid at a temperature below saturation temperature for its pressure • Superheated vapor - a vapor at a temperature above saturation temperature for its pressure • Critical point - the temperature and pressure above which there is no distinction between the liquid and vapor phases • Triple point - the temperature and pressure at which all three phases can exist in equilibrium • Vapor pressure curve - a graphical representation of the relationship between temperature and pressure at saturated conditions • Quality - the fraction of the total mass of a mixture that is in the vapor phase • Moisture Content - the fraction of the total mass of a mixture that is in the liquid phase

13. Summary (continued) Phase Change Processes • Sublimation - change of phase from solid to vapor • Vaporization - change of phase from liquid to vapor • Condensation - change of phase from vapor to liquid • Fusion or melting - change of phase from solid to liquid