Lesson 5 CHANGE 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

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