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.

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

Piston – Cylinder Arrangement

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

Vapor Pressure Curve

T-V Diagram Showing the Saturation Region

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

Constant Pressure Heat Addition

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

Pressure – Temperature Diagram

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)

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

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