Slide 1Slide 2PURE SUBSTANCEPHASES OF A PURE SUBSTANCEPHASE-CHANGE PROCESSES OF PURE SUBSTANCESSlide 6Slide 7Saturation Temperature and Saturation PressureSlide 9Some Consequences of Tsat and Psat DependencePROPERTY DIAGRAMS FOR PHASE-CHANGE PROCESSESSlide 12Slide 13Extending the Diagrams to Include the Solid PhaseSlide 15Slide 16PROPERTY TABLESSaturated Liquid and Saturated Vapor StatesSlide 19Saturated Liquid–Vapor MixtureSlide 21Slide 22Superheated VaporCompressed LiquidSlide 25Reference State and Reference ValuesTHE IDEAL-GAS EQUATION OF STATESlide 28Is Water Vapor an Ideal Gas?Slide 30Slide 31OTHER EQUATIONS OF STATESlide 33Slide 34Slide 35Slide 36SummaryCHAPTER 3PROPERTIES OF PURE SUBSTANCESLecture slides byMehmet KanogluCopyright © The McGraw-Hill Education. Permission required for reproduction or display.Thermodynamics: An Engineering Approach 8th EditionYunus A. Çengel, Michael A. BolesMcGraw-Hill, 20152Objectives•Introduce the concept of a pure substance.•Discuss the physics of phase-change processes.•Illustrate the P-v, T-v, and P-T property diagrams and P-v-T surfaces of pure substances.•Demonstrate the procedures for determining thermodynamic properties of pure substances from tables of property data.•Describe the hypothetical substance “ideal gas” and the ideal-gas equation of state.•Apply the ideal-gas equation of state in the solution of typical problems.•Introduce the compressibility factor, which accounts for the deviation of real gases from ideal-gas behavior.•Present some of the best-known equations of state.3PURE SUBSTANCE•Pure substance: A substance that has a fixed chemical composition throughout.•Air is a mixture of several gases, but it is considered to be a pure substance.4PHASES OF A PURE SUBSTANCEThe molecules in a solid are kept at their positions by the large springlike inter-molecular forces.5PHASE-CHANGE PROCESSES OF PURE SUBSTANCESSaturated liquid: A liquid that is about to vaporizeCompressed liquid (subcooled liquid): A substance that it is not about to vaporize6•Saturated vapor: A vapor that is about to condense.•Saturated liquid–vapor mixture: The state at which the liquid and vapor phases coexist in equilibrium.•Superheated vapor: A vapor that is not about to condense (i.e., not a saturated vapor).As more heat is transferred, part of the saturated liquid vaporizes (saturated liquid–vapor mixture).At 1 atm pressure, the temperature remains constant at 100°C until the last drop of liquid is vaporized (saturated vapor).As more heat is transferred, the temperature of the vapor starts to rise (superheated vapor).7T-v diagram for the heating process of water at constant pressure.If the entire process between state 1 and 5 is reversed by cooling the water while maintaining the pressure at the same value, the water will go back to state 1, retracing the same path, and in so doing, the amount of heat released will exactly match the amount of heat added during the heating process.8Saturation Temperature and Saturation PressureThe temperature at which water starts boiling depends on the pressure; therefore, if the pressure is fixed, so is the boiling temperature. Water boils at 100C at 1 atm pressure.The liquid–vapor saturation curve of a pure substance (numerical values are for water).Saturation temperature Tsat: The temperature at which a pure substance changes phase at a given pressure. Saturation pressure Psat: The pressure at which a pure substance changes phase at a given temperature.9•Latent heat: The amount of energy absorbed or released during a phase-change process. •Latent heat of fusion: The amount of energy absorbed during melting. It is equivalent to the amount of energy released during freezing. •Latent heat of vaporization: The amount of energy absorbed during vaporization and it is equivalent to the energy released during condensation.•The magnitudes of the latent heats depend on the temperature or pressure at which the phase change occurs.•At 1 atm pressure, the latent heat of fusion of water is 333.7 kJ/kg and the latent heat of vaporization is 2256.5 kJ/kg.•The atmospheric pressure, and thus the boiling temperature of water, decreases with elevation.10Some Consequences of Tsat and Psat DependenceThe variation of the temperature of fruits and vegetables with pressure during vacuum cooling from 25°C to 0°C.In 1775, ice was made by evacuating the air space in a water tank.11PROPERTY DIAGRAMS FOR PHASE-CHANGE PROCESSESThe variations of properties during phase-change processes are best studied and understood with the help of property diagrams such as the T-v, P-v, and P-T diagrams for pure substances.T-v diagram of constant-pressure phase-change processes of a pure substance at various pressures (numerical values are for water).12•saturated liquid line•saturated vapor line•compressed liquid region•superheated vapor region•saturated liquid–vapor mixture region (wet region)At supercritical pressures (P > Pcr), there is no distinct phase-change (boiling) process.Critical point: The point at which the saturated liquid and saturated vapor states are identical.1314Extending the Diagrams to Includethe Solid PhaseAt triple-point pressure and temperature, a substance exists in three phases in equilibrium.For water, Ttp = 0.01°C Ptp = 0.6117 kPa15Sublimation: Passing from the solid phase directly into the vapor phase.At low pressures (below the triple-point value), solids evaporate without melting first (sublimation).P-T diagram of pure substances.Phase Diagram16The P-v-T surfaces present a great deal of information at once, but in a thermodynamic analysis it is more convenient to work with two-dimensional diagrams, such as the P-v and T-v diagrams.17PROPERTY TABLES•For most substances, the relationships among thermodynamic properties are too complex to be expressed by simple equations.•Therefore, properties are frequently presented in the form of tables.•Some thermodynamic properties can be measured easily, but others cannot and are calculated by using the relations between them and measurable properties. •The results of these measurements and calculations are presented in tables in a convenient format.Enthalpy—A Combination PropertyThe combination u + Pv is frequently encountered in the analysis of control volumes.The product pressure  volume has energy units.18Saturated Liquid and Saturated Vapor States•Table A–4: Saturation properties of water under