CHPT02.PPT
- 1. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition 2 CHAPTER Properties of Pure Substances
- 2. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition (fig. 2-16) Constant-Pressure Phase-Change Process 2-1
- 3. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition T-v Diagram of a Pure Substance 2-2 (Fig. 2-18) Energy, not mass, crosses closed-system boundaries
- 4. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-v Diagram of a Pure Substance (Fig. 2-19) 2-3 SUPERHEATED
- 5. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-v Diagram of Substance that Contracts on Freezing (Fig. 2-21) 2-4
- 6. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-v Diagram of Substance that Expands on Freezing (Fig. 2-22) 2-5
- 7. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-T Diagram of Pure Substances (Fig. 2-25) 2-6
- 8. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-v-T Surface of a Substance that Contracts on Freezing (Fig. 2-26) 2-7
- 9. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition P-v-T Surface of a Substance that Expands on Freezing (Fig. 2-27) 2-8
- 10. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Partial List of Table A-4 (Fig. 2-35) 2-9
- 11. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Quality Shown in P-v and T-v Diagrams (Fig. 2-41) 2-10 Quality is related to the horizontal differences of P-V and T-v diagrams
- 12. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Partial List of Table A-6 (Fig. 2-45) 2-11
- 13. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Pure Substances can Exist as Compressed Liquids (Fig. 2-49) 2-12 At a given P and T, a pure substance will exist as a compressed liquid if T<T sat @ P
- 14. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition The Region Where Steam can be Treated as an Ideal Gas (Fig. 2-54) 2-13
- 15. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Comparison of Z Factors for Various Gases (Fig. 2-57) 2-14
- 16. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Percent of Error in Equations for the State of Nitrogen (Fig. 2-66) 2-15
- 17. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • A substance that has a fixed chemical composition throughout is called a pure substance. 2-16
- 18. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • A pure substance exists in different phases depending on its energy level. In the liquid phase, a substance that is not about to vaporize is called a compressed or subcooled liquid. 2-17
- 19. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • In the gas phase, a substance that is not about to condense is called a superheated vapor. 2-18
- 20. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • During a phase-change process, the temperature and pressure of a pure substance are dependent properties. At a given pressure, a substance changes phase at a fixed temperature, called the saturation temperature. At a given temperature, the pressure at which a substance changes phase is called the saturation pressure. During a boiling process, both the liquid and the vapor phases coexist in equilibrium, and under this condition the liquid is called saturated liquid and the vapor saturated vapor. 2-19
- 21. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • In a saturated liquid-vapor mixture, the mass fraction of the vapor phase is called the quality and is defined as The quality may have values between 0 (saturated liquid) and 1 (saturated vapor). It has no meaning in the compressed liquid or superheated vapor regions. 2-20
- 22. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • In the saturated mixture region, the average value of any intensive property y is determined from where f stands for saturated liquid and g for saturated vapor. 2-21
- 23. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • In the absence of compressed liquid data, a general approximation is to treat a compressed liquid as a saturated liquid at the given temperature, that is, where y stands for v, u, or h. 2-22
- 24. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • The state beyond which there is no distinct vaporization process is called the critical point. At supercritical pressures, a substance gradually and uniformly expands from the liquid to vapor phase. 2-23
- 25. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • All three phases of a substance coexist in equilibrium at states along the triple line characterized by triple-line temperature and pressure. 2-24
- 26. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • Various properties of some pure sub-stances are listed in the appendix. As can be noticed from these tables, the compressed liquid has lower v, u, and h values than the saturated liquid at the same T or P. Likewise, superheated vapor has higher v, u, and h values than the saturated vapor at the same T or P. is a major application area of thermodynamics. 2-25
- 27. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • Any relation among the pressure, temperature, and specific volume of a substance is called an equation of state. The simplest and best-known equation of state is the ideal-gas equation of state, given as where R is the gas constant. Caution should be exercised in using this relation since an ideal gas is a fictitious substance. Real gases exhibit ideal- gas behav-ior at relatively low pressures and high temperatures. 2-26
- 28. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • The deviation from ideal-gas behavior can be properly accounted for by using the compressibility factor Z, defined as 2-27
- 29. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • The Z factor is approximately the same for all gases at the same reduced temperature and reduced pressure, which are defined as where Pcr and Tcr are the critical pressure and temperature, respectively. This is known as the principle of corresponding states. (Continued on next slide) 2-28
- 30. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • When either P or T is unknown, Z can be determined from the compressibility chart with the help of the pseudo-reduced specific volume, defined as (Continued from previous slide) 2-29
- 31. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition • The P-v-T behavior of substances can be represented more accurately by the more complex equations of state. Three of the best known are van der Waals: where Chapter Summary 2-30
- 32. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • Beattie-Bridgeman: where 2-31
- 33. WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary • Benedict-Webb-Rubin: The constants appearing in the Beattie-Bridgeman and Benedict-Webb- Rubin equations are given in Table A-29 for various substances. 2-32