Review of Basic Principle of Thermodynamics 1

1. Review of Basic Principle of Thermodynamics 1 1. Properties of Pure Substances2. Heat and Work3. 1 st Law for Closed Systems4. 1 st Law for Control Volumes5. 2 nd Law of Thermodynamics6. Entropy Assoc.Prof.Sommai Priprem, PhD. Faculty of Engineering Khon Kaen University รศ.ดร.สมหมาย ปรีเปรม

2. T-v diagram of a pure substance T Critical Point P2 >P1 Tc Superheated Vapour Region Compressed Liquid Region P1 Saturated Vapour Line Saturated Liquid Line Saturated Liquid-Vapour Region v Sommai Priprem รศ.ดร.สมหมาย ปรีเปรม

3. P-v diagram of a pure substance P Critical Point Superheated Vapour Region Compressed Liquid Region Saturated Vapour Line T2 >T1 Saturated Liquid Line Saturated Liquid-Vapour Region T1 v รศ.ดร.สมหมาย ปรีเปรม

4. Thermodynamics Table • Properties Relationship are too COMPLEX • Not simple EQUATIONS can be represented • Therefore, TABLEs are more convenion • Each substance; more than one table, • Each table for each REGION ie.; • Compressed Liquid • Saturated Liquid and Saturated Vapour (2 = T table & P table) • Superheated Vapour No table for Mixture  Calculate using Saturated Table + x รศ.ดร.สมหมาย ปรีเปรม

5. Critical Constants Table T Superheated Vapor Table Compressed Liquid Table Saturated Vapour Line Saturated Liquid Line Saturated Table v Sommai Priprem รศ.ดร.สมหมาย ปรีเปรม

6. P or T mass Critical Point Piston Compressed Liquid Region Superheated Vapour Region Vapour Saturated Vapour Line Liquid Saturated Liquid Line Saturated Liquid-Vapour Region v Saturated Liquid-Vapor Mixture During vaporization (or Condenzation) process a substance exist both saturated Liquid and saturated Vapor. To analyze the mixture we need to know the QUALITY, xx = mvapor mtotal vavg = vf + xvfg uavg = uf + xufg havg = hf + xhfg savg = sf + xsfg Note 0.0 < x < 1.0 รศ.ดร.สมหมาย ปรีเปรม

7. Compressed Liquid or Subcooled Liquid When saturated liquid is subjected to higher pressure it will not Saturated any more but will becomes Compressed Liquid P or T Critical Point Superheated Vapor Region Saturated Vapour Line Compressed Liquid Region On the other hand if saturated liquid is cooled it cannot stays Saturated but will becomes Subcooled Liquid Saturated Liquid Line Saturated Liquid-Vapour Region v Data for compressed liquid is limited. In absence of Table, a property, y (i.e. v,u,s), can be approximate as y = yf @ Tsat except: h = hf@T+vf(P-Psat) รศ.ดร.สมหมาย ปรีเปรม

8. Critical Constants Table T Ideal Gas Superheated Vapor Table Compressed Liquid Table Saturated Vapour Line Saturated Liquid Line Saturated Table v รศ.ดร.สมหมาย ปรีเปรม

9. Ideal Gas • Pv =RT ideal gas equation of state • R = Ru/M kJ/kg-K • Ru = Universal gas constant = 8.3143 kJ/kmol-K = 1.868 Btu/lbmol-R = 1545 ft-lbf/lbmol-R • M = Molecular weight of the gas, kg/kMol • m = nM • n = number of mole of the gas รศ.ดร.สมหมาย ปรีเปรม

10. Pv = RT …...........(1) V=mv  PV = mRT ...............(2) m=nM, R = Ru/M  PV = (nM)(Ru/M)T PV = nRuT...............(3) For a fixed mass; Eq (2) P1V1 = mRT1and P2V2 = mRT2 P1V1 /T1 = P2V2/T2 รศ.ดร.สมหมาย ปรีเปรม

11. Generalized Compressibility Chart Z = Pv/RT Pr = P/Pcr รศ.ดร.สมหมาย ปรีเปรม

12. Compressibility Factor, Z – A measure of Deviation from Ideal-Gas Behavior Z = Pv/RT • Pr = P/Pcr = reduced pressure • Tr = T/Tcr = reduced temperature Conclusion from the chart • at low P; Pr << 1; good to assume ideal gas regardless of T • at high T; Tr > 2 ;good to assume ideal gas (except when Pr >> 1) • Near Critcal Point ; Greatest deviation from ideal gas behavior รศ.ดร.สมหมาย ปรีเปรม

13. P P P dv v Moving Boundary Work 1 Process path 2 v1 v2 รศ.ดร.สมหมาย ปรีเปรม

14. P A C P v B Work is a PATH function Amount of work involved depends not only on the initial and final state of the working fluid but also on the PROCESS as well. In this example, the beginning and final states are the same but WA>WB>WC 1 2 v1 v2 รศ.ดร.สมหมาย ปรีเปรม

15. Specific Heat • is defined as “the energy required to raise the temperature of a unit mass of a substance by one degree.” • For fluids there are two different specific heat: • Specific heat at constant volume, • Specific heat at constant pressure, รศ.ดร.สมหมาย ปรีเปรม

16. Internal Energy, Enthalpy, and Specific Heat of Ideal Gases Sp.Heat @ v; du = CvdT Sp.Heat @ p; dh = CpdT รศ.ดร.สมหมาย ปรีเปรม

17. To determine Δu and Δh of Ideal Gases 3- Ways Δu = u2 – u1 (Table) Δu = Cv,avΔT Δh  similar ways รศ.ดร.สมหมาย ปรีเปรม

18. Conclusion of Importance Equations of Chapter 3 Boundary Work; w =∫ Pdv ...........(1) 1st Law general ΣEin - ΣEout= ΔE ................(2) Closed System; Q – W = ΔU + ΔKE + ΔPE ................(3) Enthalpy (defined) h = u + Pv ...........(4) Specific Heat: du = CvdT ...........(5) dh = CpdT ...........(6) for Ideal gases: Cp = Cv + R ...........(7) k = Cp/Cv ...........(8) รศ.ดร.สมหมาย ปรีเปรม

19. State 1 Begining Between State 2 Final 1 unit of Energy The First Law of Thermodynamics : The Principle of Energy Conservation E1 + ΣEin = E2 + ΣEout ΣEin - ΣEout = E2- E1 = ΔE รศ.ดร.สมหมาย ปรีเปรม

20. Control Volume +W e i m2 m1 +Q 1st Law Equations (General) Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) • Subscripts: i = at inlet, e = at exit 1 = at time start, 2 = at time end รศ.ดร.สมหมาย ปรีเปรม

21. Total Energy of Fluid • for non-flow  mass inside control volume (cv) • enonflow = u + ke + pe kJ/kg • Enonflow = m(u + ½ V2 + zg) J • for flowing fluid  mass flowing in/out of cv. • eflow = enonflow+ flow work • eflow = u + Pv + ke + pe • defined: h = u + Pv • eflow = h + ke + pe kJ/kg • Eflow = m(h + ½ V2 + zg) J รศ.ดร.สมหมาย ปรีเปรม

22. +W +Q Sign Convention of HEAT and WORK Heat Engine System Model Add heat to system, Qin System gives WORK, Wout รศ.ดร.สมหมาย ปรีเปรม

23. 0 0 0 0 0 Control Volume +W e i m2 m1 +Q 1st Law Equations for cycles Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) Qnet = Wnet รศ.ดร.สมหมาย ปรีเปรม

24. 0 0 0 0 Control Volume +W e i m2 m1 +Q 1st Law Equations for Closed Systems Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) Q1-2 = W1-2 + (U2 – U1) +∆KE + ∆PE รศ.ดร.สมหมาย ปรีเปรม

25. 0 Control Volume +W e i m2 m1 +Q 1st Law Equations for SSSF Systems Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) รศ.ดร.สมหมาย ปรีเปรม

26. Control Surface +W e i Control Volume +Q SSSF1-inlet and 1-exit รศ.ดร.สมหมาย ปรีเปรม

27. Chapter 52nd Law of Thermodynamics Assoc.Prof.Sommai Priprem, PhD. Department of Mechanical Engineering Khon Kaen University รศ.ดร.สมหมาย ปรีเปรม

28. Summary • Processes occur in a certain direction, not in any direction. • A process will not occur unless it satisfy both 1st and 2nd law. • Importance Definitions: • Thermal Reservoir; Source, Sink • Thermal Efficiency and Heat Engine • Coefficient of Performance and Heat Pump • Reversible Process and Irreversible Process • Carnot cycle and Carnot Principles รศ.ดร.สมหมาย ปรีเปรม

29. Source, TH QH Heat Engine Wnet QL Sink, TL Thermal Efficiency Performance = desired output (5.1) required input Heat engine: Thermal efficiency = net work output (5.2) total heat input th = Wnet(5.3) Qin th = 1- QL (5.4) QH QL and QH are magnitude (amount) of heat, their direction are already accounted for in the equation. รศ.ดร.สมหมาย ปรีเปรม

30. Source, TH Source, TH QH Heat Engine Heat Engine Wnet QL Sink, TL QH Wnet QL = 0 The Second Law of Thermodynamics:Kelvin-Planck Statement It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work meaning: QL > 0 from th = Wnet = 1- QL QH QH No heat engine can have a thermal efficiency of 100 % Impossible Possible รศ.ดร.สมหมาย ปรีเปรม

31. QH High-Temp. Body, TH High-Temp. Body, TH W Q Heat Pump QL Low-Temp. Body, TL Low-Temp. Body, TL The Second Law of Thermodynamics:Clausuis Statement It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. meaning: W> 0 from COP = Q W No heat pump can have a COP of  Possible Impossible รศ.ดร.สมหมาย ปรีเปรม

32. High-temp. reservoir, TH Low-temp. reservoir, TL 1 Irrev. HE 2 rev. HE 3 rev. HE The Carnot Principles • The efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs. • The efficiency of all reversible heat engines operating between the same two reservoirs are the same. th,1 < th,2 th,2 = th,3 รศ.ดร.สมหมาย ปรีเปรม

33. Source, TH QH Heat Engine Wnet QL Sink, TL Reversible Cycle QH/QL= TH/TL (5.7) The Carnot Efficiency Heat Engine:th = 1- QLth,rev = 1 -TL(5.9) QHTH Refrigerator COPR = 1COPR,rev = 1 (5.10) QH /QL – 1 TH /TL – 1 Heat Pump COPHP = 1  COPHP,rev = 1 (5.11) 1 –QL/QH 1 - TL/TH รศ.ดร.สมหมาย ปรีเปรม

34. Chapter 6 ENTROPY รศ.ดร.สมหมาย ปรีเปรม

35. Source, TH QH Heat Engine Wrev QL Sink, TL Inequality of CLAUSIUS รศ.ดร.สมหมาย ปรีเปรม

36. 1 A B C 2 ENTROPY: A Property of a System Consider Two Reversible Cycles A-B and A-C รศ.ดร.สมหมาย ปรีเปรม

37. Two Important Thermodynamics Relations Consider a internally reversible CLOSED system; 1st Law δQ = dU + δW TdS = dU +PdV T ds = du + Pdv .........(6.4) but h = u + Pv  dh = du + d(Pv) dh = du + Pdv + vdP substitute in (6.4) Tds = dh – vdP .........(6.5) รศ.ดร.สมหมาย ปรีเปรม

38. Principle of Increase of Entropy Surroundings, temperature = T0 Q W System, temperature = T รศ.ดร.สมหมาย ปรีเปรม

39. Entropy Change of a Solid or Liquid Solid & Liquid  • Specific Heat = Constant • ΔV very small  Δh~Δu ~q • ds = (Q/T)rev  du/T  CdT/T s2-s1  C ln(T2/T1) รศ.ดร.สมหมาย ปรีเปรม

40. Entropy Change of an Ideal Gas รศ.ดร.สมหมาย ปรีเปรม

41. Isentropic Process of Ideal Gases รศ.ดร.สมหมาย ปรีเปรม

42. Reversible Polytropic Process of Ideal Gases รศ.ดร.สมหมาย ปรีเปรม

43. Second Law Efficiency รศ.ดร.สมหมาย ปรีเปรม

44. END รศ.ดร.สมหมาย ปรีเปรม