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 P cr and T cr 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