1. Thermodynamics UNIT – I S.E.

2. Thermodynamics

3. Thermodynamics Prerequisites: - Prerequisites: - 1. Engineering Mathematics 2. Engineering Physics/Chemistry 3. Fundamental Concepts and laws of Thermodynamics.

4. Thermodynamics Course Objectives: Course Objectives: Identify and use units and notations in Thermodynamics. Identify and use units and notations in Thermodynamics. State and illustrate first and second laws of Thermodynamics. State and illustrate first and second laws of Thermodynamics. Explain the concepts of entropy, enthalpy, reversibility and irreversibility. Explain the concepts of entropy, enthalpy, reversibility and irreversibility. Apply the first and second laws of Thermodynamics to various gas processes and cycles. Apply the first and second laws of Thermodynamics to various gas processes and cycles. To get conversant with properties of steam, dryness fraction measurement, vapor processes and Thermodynamic vapor cycles, performance estimation. To get conversant with properties of steam, dryness fraction measurement, vapor processes and Thermodynamic vapor cycles, performance estimation. To get conversant with Psychrometric Charts, Psychrometric processes, human comfort conditions. To get conversant with Psychrometric Charts, Psychrometric processes, human comfort conditions.

5. Thermodynamics Course Outcomes: Course Outcomes: On completion of the course, learner will be able to– Apply various laws of thermodynamics to various processes and real systems. Apply various laws of thermodynamics to various processes and real systems. Apply the concept of Entropy, Calculate heat, work and other important thermodynamic properties for various ideal gas processes. Apply the concept of Entropy, Calculate heat, work and other important thermodynamic properties for various ideal gas processes. Estimate performance of various Thermodynamic gas power cycles and gas refrigeration cycle and availability in each case. Estimate performance of various Thermodynamic gas power cycles and gas refrigeration cycle and availability in each case. Estimate the condition of steam and performance of vapour power cycle and vapour compression cycle. Estimate the condition of steam and performance of vapour power cycle and vapour compression cycle. Estimate Stoichiometric air required for combustion, performance of steam generators and natural draught requirements in boiler plants. Estimate Stoichiometric air required for combustion, performance of steam generators and natural draught requirements in boiler plants. Use Psychrometric charts and estimate various essential properties related to Psychrometry and processes. Use Psychrometric charts and estimate various essential properties related to Psychrometry and processes.

6. Thermodynamics Syllabus: Syllabus: Unit I : Laws of thermodynamics Unit I : Laws of thermodynamics Unit II : Entropy & Ideal Gas definition Gas Laws Unit II : Entropy & Ideal Gas definition Gas Laws Unit III : Thermodynamic cycles : Gas Power Cycles Unit III : Thermodynamic cycles : Gas Power Cycles & Refrigeration Cycle ; Availability & Refrigeration Cycle ; Availability Unit IV: Properties of Pure substances : Vapour Unit IV: Properties of Pure substances : Vapour Power Cycles & Vapour Refrigeration Cycles Power Cycles & Vapour Refrigeration Cycles ;Thermodynamic Vapour Cycle ;Thermodynamic Vapour Cycle Unit V : Steam Generators Unit V : Steam Generators Unit VI : Psychrometry Unit VI : Psychrometry

7. Thermodynamics Unit I : Laws of thermodynamics Introduction of thermodynamics, Introduction of thermodynamics, Review of basic definitions, Review of basic definitions, Zeroth law of thermodynamics, Zeroth law of thermodynamics, Macro and Microscopic Approach, Macro and Microscopic Approach, State Postulate, State Postulate, State, Process and Thermodynamic Cycles, State, Process and Thermodynamic Cycles, First law of thermodynamics, Joules experiment, First law of thermodynamics, Joules experiment, Applications of first law to flow and non flow processes and cycles. Applications of first law to flow and non flow processes and cycles. Steady flow energy equation and its application to different devices. Steady flow energy equation and its application to different devices. Equivalence of Clausius and Kelvin Planck Statement, Equivalence of Clausius and Kelvin Planck Statement, PMM I and II, PMM I and II, Concept of Reversibility and Irreversibility. Concept of Reversibility and Irreversibility.

9. Introduction THERMODYNAMICS: THERMODYNAMICS: It is the science of the relations between heat, Work and the properties of the systems. It is the science of the relations between heat, Work and the properties of the systems. Examples: Examples: If we like to: If we like to: o Rise the temperature of water in kettle o Burn some fuel in the combustion chamber of an engine. o Cool our room on a hot humid day. o Heat up our room on a cold winter night.

10. Thermodynamic System A thermodynamic system, or simply a system, is defined as a quantity of matter or a region in space chosen for study. A thermodynamic system, or simply a system, is defined as a quantity of matter or a region in space chosen for study. Anything outside the system is called the surroundings. Anything outside the system is called the surroundings. The real or imaginary surface that separates the system from it surroundings is called the boundary. The real or imaginary surface that separates the system from it surroundings is called the boundary. The boundary of a system may be fixed or movable. The boundary of a system may be fixed or movable.

11. Thermodynamic System Closed system (or control mass) : Closed system (or control mass) : It consists of a fixed amount of mass. No mass can enter or leave a closed system, but energy, on the other hand, may cross the boundary in the forms of heat or work. It consists of a fixed amount of mass. No mass can enter or leave a closed system, but energy, on the other hand, may cross the boundary in the forms of heat or work. e.g. piston/cylinder e.g. piston/cylinder Open system (or control volume) : Open system (or control volume) : Both energy and mass may cross the boundary of a control volume, which is called the control surface. Both energy and mass may cross the boundary of a control volume, which is called the control surface. e.g. compressor, turbine, heat exchanger, etc e.g. compressor, turbine, heat exchanger, etc

13. Thermodynamic System

24. Thermodynamic Work & Heat Thermodynamic definition of work: Thermodynamic definition of work: Positive work is done by a system when the sole effect external to the system could be reduced to the rise of a weight. Positive work is done by a system when the sole effect external to the system could be reduced to the rise of a weight. Heat to work Thermal power plant Heat to work Thermal power plant Thermodynamic definition of heat: Thermodynamic definition of heat: It is the energy in transition between the system and the surroundings by virtue of the difference in temperature. It is the energy in transition between the system and the surroundings by virtue of the difference in temperature. Work to heat Refrigeration Work to heat Refrigeration

25. Sign Conventions

26. First Law of Thermodynamics First Law of Thermodynamics

28. Construction of a Temperature Scale Choose fixed point temperatures that are easy to reconstruct in any lab, e.g. freezing point of water, boiling point of water, or anything else you can think of. Choose fixed point temperatures that are easy to reconstruct in any lab, e.g. freezing point of water, boiling point of water, or anything else you can think of. Fahrenheit: Original idea: Fahrenheit: Original idea: 0  FFreezing point of Salt/ice 100  F Body Temperature Celsius (Centigrade) Scale: Celsius (Centigrade) Scale: 0  CIce Melts 100  CWater Boils Note a change of 1  C = a change of 1.8  F. Note a change of 1  C = a change of 1.8  F.

29. Conversion between Fahrenheit and Celsius

30. Absolute or Kelvin Scale The lowest possible temperature on the Celsius Scale is -273  C. The lowest possible temperature on the Celsius Scale is -273  C. The Kelvin Scale just takes this value and calls it 0K, or absolute zero. The Kelvin Scale just takes this value and calls it 0K, or absolute zero. Note: the “size” of 1K is the same as 1  C. Note: the “size” of 1K is the same as 1  C. To convert from C to K just add 273. To convert from C to K just add 273.K=C+273

31. When do you use which scale. Never use Fahrenheit, except for the weather. Never use Fahrenheit, except for the weather. You can always use Kelvin and you must use Kelvin when doing absolute temperature measurements. You can always use Kelvin and you must use Kelvin when doing absolute temperature measurements. You can use either Kelvin or Celsius when measuring differences in temperature. You can use either Kelvin or Celsius when measuring differences in temperature.

32. Specific Heat Observational Fact: It is easy to change the temperature of some things (e.g. air) and hard to change the temperature of others (e.g. water) Observational Fact: It is easy to change the temperature of some things (e.g. air) and hard to change the temperature of others (e.g. water) The amount of heat (Q) added into a body of mass m to change its temperature by an amount  T is given by The amount of heat (Q) added into a body of mass m to change its temperature by an amount  T is given by Q=m C  T C is called the specific heat and depends on the material and the units used. C is called the specific heat and depends on the material and the units used.

33. Units of Specific Heat Note that by definition, the specific heat of water is 1 cal/g  C.

34. Material J/kg  C cal/g  C Water41861 Ice20900.50 Steam20100.48 Silver2340.056 Aluminum9000.215 Copper3870.0924 Gold1290.0308 Iron4480.107 Lead1280.0305 Brass3800.092 Glass8370.200 Wood17000.41 Ethyl Alcohol 24000.58 Beryllium18300.436

35. Work Done by a Gas Work=(Force)x(distance) Work=(Force)x(distance) =F  y Force=(Pressure)x(Area) Force=(Pressure)x(Area) W= P (A  y) W= P (A  y) W=P  V

36. First Law of Thermodynamics Conservation of energy When heat is added into a system it can either 1) change the internal energy of the system (i.e. make it hotter) or 2) go into doing work. When heat is added into a system it can either 1) change the internal energy of the system (i.e. make it hotter) or 2) go into doing work. Q=W +  U. Note: For our purposes, Internal Energy is the part of the energy that depends on Temperature.

37. Steady Flow Energy Equation: All the practical systems involve flow of mass across the boundary separating the system and the surroundings. All the practical systems involve flow of mass across the boundary separating the system and the surroundings. Whether it be a steam turbine or a gas turbine or a compressor or an automobile engine there exists flow of gases/gas mixtures into and out of the system. Whether it be a steam turbine or a gas turbine or a compressor or an automobile engine there exists flow of gases/gas mixtures into and out of the system.

38. Steady Flow Energy Equation: Let u1 be the specific internal energy of the fluid entering K1 be the velocity of the fluid while entering Z1 be the potential energy of the fluid while entering Similarly let u2,K2 and Z2 be respective entities while leaving.

39. Steady Flow Energy Equation: Total Energy at Inlet Total Energy at Inlet E 1 = Int. E +Kin. E+ Pot. E E 1 = Int. E +Kin. E+ Pot. E = Q 1 + du 1 + V 1 2 /2 + Z 1 = Q 1 + du 1 + V 1 2 /2 + Z 1 The Energy at outlet / exit The Energy at outlet / exit E 2 = Int. E +Kin. E+ Pot. E E 2 = Int. E +Kin. E+ Pot. E = W 1 +du 1 + V 2 2 /2 + Z 2 = W 1 +du 1 + V 2 2 /2 + Z 2 For Steady Flow Process; For Steady Flow Process; E 1 = E 2 E 1 = E 2

40. Steady Flow Energy Equation: h 1 = u 1 +p 1 v 1 & h 2 = u 2 +p 2 v 2 h 1 = u 1 +p 1 v 1 & h 2 = u 2 +p 2 v 2 Q-W = (h 2 – h 1 ) + (V 2 2 /2 -V 1 2 /2 ) + (Z 2 - Z 1 ) Q-W = (h 2 – h 1 ) + (V 2 2 /2 -V 1 2 /2 ) + (Z 2 - Z 1 ) This is the SFEE This is the SFEE

41. Steady Flow Energy Equation: If the kinetic energies at entry and exit are small compared to the enthalpies and there is no difference in the levels of entry and exit If the kinetic energies at entry and exit are small compared to the enthalpies and there is no difference in the levels of entry and exit q-w=(h 2 – h 1 )= Δh ; per unit mass basis q-w=(h 2 – h 1 )= Δh ; per unit mass basis or Q-W= m Δh or Q-W= m Δh Pv is called the “flow work”. This is not thermodynamic work and can’t rise any weight, but necessary to establish the flow. Pv is called the “flow work”. This is not thermodynamic work and can’t rise any weight, but necessary to establish the flow. For an adiabatic process q = 0 For an adiabatic process q = 0 -w = Δh -w = Δh

42. Throttling process Consider a throttling process Consider a throttling process 1 2 1 2 There is no work done W=0 There is no work done W=0 If there is no heat transfer Q =0 If there is no heat transfer Q =0 Conservation of mass requires that V 1 =V 2 Conservation of mass requires that V 1 =V 2 Since 1 and 2 are at the same level Z 1 =Z 2 Since 1 and 2 are at the same level Z 1 =Z 2 From SFEE it follows that h 1 = h 2 From SFEE it follows that h 1 = h 2 Conclusion: Throttling is a constant enthalpy process (isenthalpic process) Conclusion: Throttling is a constant enthalpy process (isenthalpic process)

43. Heat Exchanger For Hot fluid W = 0 For Hot fluid W = 0 Qg=mg (hg2-hg1) Qg=mg (hg2-hg1) For Cold fluid For Cold fluid Qf=mf(hf2-hf1) Qf=mf(hf2-hf1)

44. Heat Engines If we can create an “engine” that operates in a cycle, we return to our starting point each time and therefore have the same internal energy. Thus, for a complete cycle If we can create an “engine” that operates in a cycle, we return to our starting point each time and therefore have the same internal energy. Thus, for a complete cycleQ=W

45. Model Heat Engine Q hot = W+Q cold Q hot = W+Q coldor Q hot - Q cold =W Q hot - Q cold =W (what goes in must come out)

46. Efficiency We want to write an expression that describes how well our heat engine works. We want to write an expression that describes how well our heat engine works. Q hot =energy that you pay for. Q hot =energy that you pay for. W=work done (what you want.) W=work done (what you want.) Q cold = Waste energy (money). Q cold = Waste energy (money). Efficiency = e = W/Q hot

47. If we had a perfect engine, all of the input heat would be converted into work and the efficiency would be 1. If we had a perfect engine, all of the input heat would be converted into work and the efficiency would be 1. The worst possible engine is one that does no work and the efficiency would be zero. The worst possible engine is one that does no work and the efficiency would be zero. Real engines are between 0 and 1 Real engines are between 0 and 1

48. Second Law of Thermodynamics  Kelvin- Planck Statement: It is impossible to build a cyclic machine that converts heat into work with 100% efficiency It is impossible to build a cyclic machine that converts heat into work with 100% efficiency  It is impossible to construct a cyclic machine that completely (with 100% efficiency) converts heat into equivalent amount of work. All heat engines have e<1. (Not all heat can be converted into work.) All heat engines have e<1. (Not all heat can be converted into work.)

49. Second Law of Thermodynamics

51.  Clausius Statement: Heat does not ‘flow’ from a colder body to a hotter body, without an external work input. Heat does not ‘flow’ from a colder body to a hotter body, without an external work input.  This automatically implies that the spontaneous direction of the ‘flow of heat’ is from a hotter body to a colder body.  The Kelvin’s and Clausius’s statements of the second law are equivalent. i.e. if we violate Kelvin’s statement, then we will automatically violate the Clausius’s statement of the second law (and vice- versa).

52. Second Law of Thermodynamics

53. Coefficient of Performance for refrigerator : It is a ratio of desired output to the input

54. Second Law of Thermodynamics Coefficient of Performance for Heat Pump : It is a ratio of desired output to the input

55. Carnot Engine The very best theoretically possible heat engine is the Carnot engine. The very best theoretically possible heat engine is the Carnot engine. The efficiency of a Carnot engine depends on the temperature of the hot and cold reservoirs. The efficiency of a Carnot engine depends on the temperature of the hot and cold reservoirs.

56. The Third Law For substances in internal equilibrium, undergoing an isothermal process, the entropy change goes to zero as T (in K) goes to zero. For substances in internal equilibrium, undergoing an isothermal process, the entropy change goes to zero as T (in K) goes to zero.  The law is valid for pure substances and mixtures.  Close to Zero Kelvin, the molecular motions have to be treated using quantum mechanics → still it is found that quantum ideal gases obey the third law.

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