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ENERGY, ENERGYTRANSFER AND ENERGY     ANALYSIS                                    Lecture 5          Keith Vaugh BEng (AER...
OBJECTIVES             }             KEITH VAUGH
OBJECTIVESIntroduce the concept of energy and define itsvarious forms.                                                }    ...
OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy.               ...
OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy.               ...
OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy.               ...
OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy.               ...
}KEITH VAUGH
Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system.           ...
Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system.           ...
Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system.           ...
Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system.           ...
FORMS OF ENERGYEnergy can exist in numerous forms such as thermal, mechanical,kinetic, potential, electric, magnetic, chem...
}Kinetic energy, KEThe energy that a systempossesses as a result of its motionrelative to some reference frame.           ...
}Kinetic energy, KE                        1   2                                      KE = mV     ( kJ )The energy that a ...
}Kinetic energy, KE                         1   2                                       KE = mV             ( kJ )The ener...
}Kinetic energy, KE                         1   2                                       KE = mV             ( kJ )The ener...
}Kinetic energy, KE                         1   2                                       KE = mV              ( kJ )The ene...
}Kinetic energy, KE                         1   2                                       KE = mV              ( kJ )The ene...
KEITH VAUGH
Mass flow rate   &    &   m = ρV = ρ AcVavg   ( s)                       kg                              KEITH VAUGH
Mass flow rate    &    &    m = ρV = ρ AcVavg        ( s)                              kgEnergy flow rate   & &   E = me    ...
Total energy of a system                          1  2     E = U + KE + PE = U + mV + mgz   ( kJ )                        ...
Total energy of a system                          1  2     E = U + KE + PE = U + mV + mgz          ( kJ )                 ...
Total energy of a system                          1  2     E = U + KE + PE = U + mV + mgz          ( kJ )                 ...
MECHANICAL ENERGYThe form of energy that can be converted to mechanical workcompletely and directly by an ideal mechanical...
MECHANICAL ENERGYThe form of energy that can be converted to mechanical workcompletely and directly by an ideal mechanical...
Rate of mechanical energy of a flowing fluid&                    ⎛ P V 2      ⎞        &Emech = memech     &              ...
Rate of mechanical energy of a flowing fluid&                    ⎛ P V 2      ⎞        &Emech = memech     &              ...
Rate of mechanical energy of a flowing fluid&                    ⎛ P V 2      ⎞        &Emech = memech     &              ...
ENERGY TRANSFER BY HEAT        Heat        The form of energy that is transferred between        two systems (or a system ...
ENERGY TRANSFER BY HEAT        Heat        The form of energy that is transferred between        two systems (or a system ...
ENERGY TRANSFER BY HEAT        Heat        The form of energy that is transferred between        two systems (or a system ...
ENERGY TRANSFER BY HEAT        Heat        The form of energy that is transferred between        two systems (or a system ...
During an adiabatic process, a systemexchanges no heat with its surroundings                                          KEIT...
ENERGY TRANSFER BY WORK                               Work                               The energy transfer associated wi...
ENERGY TRANSFER BY WORK                               Work                               The energy transfer associated wi...
KEITH VAUGH
Heat Vs. WorkBoth are recognised at the boundaries of asystem as they cross the boundaries. That is,both heat and work are...
KEITH VAUGH
Properties are point functions; but heat and workare path functions (their magnitudes depend on thepath followed          ...
Properties are point functions                                                     and have exact differentials (d).      ...
Properties are point functions                                                     and have exact differentials (d).      ...
ELECTRICAL WORK                                                   }Electrical power in terms of resistanceR, current I, an...
ELECTRICAL WORK                                            Electrical Work                                               W...
ELECTRICAL WORK                                            Electrical Work                                               W...
ELECTRICAL WORK                                            Electrical Work                                               W...
ELECTRICAL WORK                                            Electrical Work                                               W...
MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist ...
MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist ...
MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist ...
KEITH VAUGH
Shaft work is proportional to the torque applied and the number of revolutions                             of the shaft   ...
A force (F) acting through a momentarm (r) generates a torque (T)                T   T = Fr → F =                r        ...
A force (F) acting through a momentarm (r) generates a torque (T)                T   T = Fr → F =                rThis for...
A force (F) acting through a momentarm (r) generates a torque (T)                T   T = Fr → F =                rThis for...
A force (F) acting through a momentarm (r) generates a torque (T)                T   T = Fr → F =                rThis for...
KEITH VAUGH
Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work don...
Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work don...
Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work don...
KEITH VAUGH
Work done on Elastic Solid Bars            2         2 Welastic = ∫ F dx = ∫ σ n A dx           1         1               ...
Work done on Elastic Solid Bars            2         2 Welastic = ∫ F dx = ∫ σ n A dx           1         1               ...
KEITH VAUGH
Work done to raise or to accelerate a bodyThe work transfer needed to raise a body isequal to the change in the potential ...
Non-mechanical forms of workElectrical workThe generalised force is the voltage (the electricalpotential) and the generali...
FIRST LAW OF THERMODYNAMICS     The first law of thermodynamics (the conservation of     energy principle) provides a sound...
FIRST LAW OF THERMODYNAMICS     The first law of thermodynamics (the conservation of     energy principle) provides a sound...
The First LawFor all adiabatic processes between two specifiedstates of a closed system, the net work done is thesame regar...
KEITH VAUGH
In the absence of any workinteractions, the energy change ofa system is equal to the net heattransfer                     ...
In the absence of any work           The work (electrical) done on aninteractions, the energy change of   adiabatic system...
ENERGY BALANCE                 }                 KEITH VAUGH
ENERGY BALANCEThe net change (increase or decrease) in the total energy of thesystem during a process is equal to the diff...
ENERGY BALANCE    The net change (increase or decrease) in the total energy of the    system during a process is equal to ...
ENERGY BALANCE    The net change (increase or decrease) in the total energy of the    system during a process is equal to ...
KEITH VAUGH
The work (boundary) done on anadiabatic system is equal to theincrease in the energy of thesystem                         ...
The work (boundary) done on an     The energy change of a systemadiabatic system is equal to the   during a process is equ...
Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state                         ...
Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state   ΔEsystem = E final = E...
Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state   ΔEsystem = E final = E...
Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state   ΔEsystem = E final = E...
Mechanisms of Energy Transfer, Ein and EoutEnergy can be transferred to or from a system in three forms  ✓ Heat transfer  ...
Mechanisms of Energy Transfer, Ein and EoutEnergy can be transferred to or from a system in three forms  ✓ Heat transfer  ...
Mechanisms of Energy Transfer, Ein and Eout   Energy can be transferred to or from a system in three forms     ✓ Heat tran...
Mechanisms of Energy Transfer, Ein and Eout   Energy can be transferred to or from a system in three forms     ✓ Heat tran...
The energy balance can be expressed in a per unit mass basis  ein − eout = Δesystem   ( kg)                          kJ   ...
The energy balance can be expressed in a per unit mass basis  ein − eout = Δesystem   ( kg)                          kJThe...
The energy balance can be expressed in a per unit mass basis   ein − eout = Δesystem      ( kg)                           ...
The energy balance can be expressed in a per unit mass basis   ein − eout = Δesystem       ( kg)                          ...
The energy balance can be expressed in a per unit mass basis   ein − eout = Δesystem           ( kg)                      ...
ENERGY CONVERSION               EFFICIENCIESEfficiencyis one of the most frequently used terms in thermodynamics,and it ind...
ENERGY CONVERSION                EFFICIENCIESEfficiencyis one of the most frequently used terms in thermodynamics,and it in...
Q    Amount of heat released during combustionηcombustion   =    =                HV       Heating value of the fuel burne...
The efficiency of space heating systems of                                                 residential and commercial build...
GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical powe...
GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical powe...
GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical powe...
Using energy-efficient appliances conserve energy.It helps the environment by reducing the amount ofpollutants emitted to t...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
Efficiencies of mechanical and electrical devices           Mechanical energy output Emech, out      Emech, loss ηmech   = ...
The mechanical efficiency of a fan is the ratioof the kinetic energy of air at the fan exit tothe mechanical power input   ...
&                                                                                   ⎛ mV22 ⎞                            ...
&                                                                                   ⎛ mV22 ⎞                            ...
&                                                                                   ⎛ mV22 ⎞                            ...
&           Mechanical power output Wshaft , outηmotor   =                        =                                 Pump e...
Forms of energyEnergy transfer by heatEnergy transfer by workMechanical forms of workThe first law of thermodynamics    En...
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SSL5 Energy Transfer and Analysis

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Forms of energy
Energy transfer by heat
Energy transfer by work
Mechanical forms of work
The first law of thermodynamics
Energy balance
Energy change of a system
Mechanisms of energy transfer (heat, work, mass flow)
Energy conversion efficiencies
Efficiencies of mechanical and electrical devices (turbines, pumps, etc...)

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  • Recall that the units of Q and W are kJ\n
  • Recall that the units of Q and W are kJ\n
  • Recall that the units of Q and W are kJ\n
  • Recall that the units of Q and W are kJ\n
  • Recall that the units of Q and W are kJ\n
  • Recall that the units of Q and W are kJ\n
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  • Transcript of "SSL5 Energy Transfer and Analysis"

    1. 1. ENERGY, ENERGYTRANSFER AND ENERGY ANALYSIS Lecture 5 Keith Vaugh BEng (AERO) MEng Reference text: Chapter 3 - Fundamentals of Thermal-Fluid Sciences, 3rd Edition Yunus A. Cengel, Robert H. Turner, John M. Cimbala McGraw-Hill, 2008 KEITH VAUGH
    2. 2. OBJECTIVES } KEITH VAUGH
    3. 3. OBJECTIVESIntroduce the concept of energy and define itsvarious forms. } KEITH VAUGH
    4. 4. OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy. } KEITH VAUGH
    5. 5. OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy. }Define the concept of heat and the terminologyassociated with energy transfer by heat. KEITH VAUGH
    6. 6. OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy. }Define the concept of heat and the terminologyassociated with energy transfer by heat.Discuss the three mechanisms of heat transfer:conduction, convection, and radiation. KEITH VAUGH
    7. 7. OBJECTIVESIntroduce the concept of energy and define itsvarious forms.Discuss the nature of internal energy. }Define the concept of heat and the terminologyassociated with energy transfer by heat.Discuss the three mechanisms of heat transfer:conduction, convection, and radiation.Define the concept of work, including electricalwork and several forms of mechanical work. KEITH VAUGH
    8. 8. }KEITH VAUGH
    9. 9. Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system. } KEITH VAUGH
    10. 10. Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system. }Determine that a fluid flowing across a controlsurface of a control volume carries energy acrossthe control surface in addition to any energy transferacross the control surface that may be in the form ofheat and/or work. KEITH VAUGH
    11. 11. Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system. }Determine that a fluid flowing across a controlsurface of a control volume carries energy acrossthe control surface in addition to any energy transferacross the control surface that may be in the form ofheat and/or work.Define energy conversion efficiencies. KEITH VAUGH
    12. 12. Introduce the first law of thermodynamics, energybalances, and mechanisms of energy transfer to orfrom a system. }Determine that a fluid flowing across a controlsurface of a control volume carries energy acrossthe control surface in addition to any energy transferacross the control surface that may be in the form ofheat and/or work.Define energy conversion efficiencies.Discuss the implications of energy conversion onthe environment. KEITH VAUGH
    13. 13. FORMS OF ENERGYEnergy can exist in numerous forms such as thermal, mechanical,kinetic, potential, electric, magnetic, chemical, and nuclear, andtheir sum constitutes the total energy, E of a system. }Thermodynamics deals only with the change of the total energy.Macroscopic forms of energyThose a system possesses as a whole with respect to some outsidereference frame, such as kinetic and potential energies.Microscopic forms of energyThose related to the molecular structure of a system and thedegree of the molecular activity.Internal energy, UThe sum of all the microscopic forms of energy. KEITH VAUGH
    14. 14. }Kinetic energy, KEThe energy that a systempossesses as a result of its motionrelative to some reference frame. KEITH VAUGH
    15. 15. }Kinetic energy, KE 1 2 KE = mV ( kJ )The energy that a system 2possesses as a result of its motionrelative to some reference frame. KEITH VAUGH
    16. 16. }Kinetic energy, KE 1 2 KE = mV ( kJ )The energy that a system 2possesses as a result of its motionrelative to some reference frame. V2 ke = 2 ( kg) kJ Per unit mass KEITH VAUGH
    17. 17. }Kinetic energy, KE 1 2 KE = mV ( kJ )The energy that a system 2possesses as a result of its motionrelative to some reference frame. V2 ke = 2 ( kg) kJ Per unit mass }Potential energy, PEThe energy that a systempossesses as a result of itselevation in a gravitational field. KEITH VAUGH
    18. 18. }Kinetic energy, KE 1 2 KE = mV ( kJ )The energy that a system 2possesses as a result of its motionrelative to some reference frame. V2 ke = 2 ( kg) kJ Per unit mass }Potential energy, PE PE = mgz ( kJ )The energy that a systempossesses as a result of itselevation in a gravitational field. KEITH VAUGH
    19. 19. }Kinetic energy, KE 1 2 KE = mV ( kJ )The energy that a system 2possesses as a result of its motionrelative to some reference frame. V2 ke = 2 ( kg) kJ Per unit mass }Potential energy, PE PE = mgz ( kJ )The energy that a systempossesses as a result of itselevation in a gravitational field. pe = gz ( kg) kJ Per unit mass KEITH VAUGH
    20. 20. KEITH VAUGH
    21. 21. Mass flow rate & & m = ρV = ρ AcVavg ( s) kg KEITH VAUGH
    22. 22. Mass flow rate & & m = ρV = ρ AcVavg ( s) kgEnergy flow rate & & E = me ( kJ s or kW ) KEITH VAUGH
    23. 23. Total energy of a system 1 2 E = U + KE + PE = U + mV + mgz ( kJ ) 2 KEITH VAUGH
    24. 24. Total energy of a system 1 2 E = U + KE + PE = U + mV + mgz ( kJ ) 2Energy of a system per unit mass V2 e = u + ke + pe = u + 2 + gz ( kg) kJ KEITH VAUGH
    25. 25. Total energy of a system 1 2 E = U + KE + PE = U + mV + mgz ( kJ ) 2Energy of a system per unit mass V2 e = u + ke + pe = u + 2 + gz ( kg) kJTotal energy per unit mass E e= m ( kg) kJ KEITH VAUGH
    26. 26. MECHANICAL ENERGYThe form of energy that can be converted to mechanical workcompletely and directly by an ideal mechanical device suchas an ideal turbine }Kinetic and Potential energies are the familiar forms ofmechanical energy KEITH VAUGH
    27. 27. MECHANICAL ENERGYThe form of energy that can be converted to mechanical workcompletely and directly by an ideal mechanical device suchas an ideal turbine }Kinetic and Potential energies are the familiar forms ofmechanical energy P V2 Mechanical energy of a emech = + + gz ρ 2 flowing fluid per unit mass KEITH VAUGH
    28. 28. Rate of mechanical energy of a flowing fluid& ⎛ P V 2 ⎞ &Emech = memech & = m ⎜ + + gz ⎟ ⎝ ρ 2 ⎠ KEITH VAUGH
    29. 29. Rate of mechanical energy of a flowing fluid& ⎛ P V 2 ⎞ &Emech = memech & = m ⎜ + + gz ⎟ ⎝ ρ 2 ⎠Mechanical energy change of a fluid during incompressible flow per unit mass P2 − P1 V22 − V12Δemech = ρ + 2 + g ( z2 − z1 ) ( kg) kJ KEITH VAUGH
    30. 30. Rate of mechanical energy of a flowing fluid& ⎛ P V 2 ⎞ &Emech = memech & = m ⎜ + + gz ⎟ ⎝ ρ 2 ⎠Mechanical energy change of a fluid during incompressible flow per unit mass P2 − P1 V22 − V12Δemech = ρ + 2 + g ( z2 − z1 ) ( kg) kJRate of mechanical energy change of a fluid during incompressible flow & ⎛ P2 − P1 V22 − V12 ⎞ &ΔEmech = mΔemech & = m ⎜ + + g ( z2 − z1 )⎟ ( kW ) ⎝ ρ 2 ⎠ KEITH VAUGH
    31. 31. ENERGY TRANSFER BY HEAT Heat The form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature differential } KEITH VAUGH
    32. 32. ENERGY TRANSFER BY HEAT Heat The form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature differential } Heat transfer per unit mass Q q= m ( kg) kJ KEITH VAUGH
    33. 33. ENERGY TRANSFER BY HEAT Heat The form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature differential } Heat transfer per unit mass Q q= m ( kg) kJ Amount of heat transfer when heat transfer rate is constant & Q = QΔt ( kJ ) KEITH VAUGH
    34. 34. ENERGY TRANSFER BY HEAT Heat The form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature differential } Heat transfer per unit mass Q q= m ( kg) kJ Amount of heat transfer when heat transfer rate is constant & Q = QΔt ( kJ ) Amount of heat transfer when heat transfer rate changes with time & t2 Q = ∫ Qdt t1 ( kJ ) KEITH VAUGH
    35. 35. During an adiabatic process, a systemexchanges no heat with its surroundings KEITH VAUGH
    36. 36. ENERGY TRANSFER BY WORK Work The energy transfer associated with a force acting through a distance. } Heat transfer to a system and work done by a system are positive; heat transfer from a system and work done on a system are negativeSpecifying the directions of Alternative is to use the subscripts in and out toheat and work indicate the direction KEITH VAUGH
    37. 37. ENERGY TRANSFER BY WORK Work The energy transfer associated with a force acting through a distance. } Heat transfer to a system and work done by a system are positive; heat transfer from a system and work done on a system are negativeSpecifying the directions of Alternative is to use the subscripts in and out toheat and work indicate the direction Work done per unit mass W w= m ( kg) kJ KEITH VAUGH
    38. 38. KEITH VAUGH
    39. 39. Heat Vs. WorkBoth are recognised at the boundaries of asystem as they cross the boundaries. That is,both heat and work are boundary phenomena.Systems possess energy, but not heat or work.Both are associated with a process, not a state.Unlike properties, heat or work has no meaningat a state.Both are path functions (i.e., their magnitudesdepend on the path followed during a process aswell as the end states). KEITH VAUGH
    40. 40. KEITH VAUGH
    41. 41. Properties are point functions; but heat and workare path functions (their magnitudes depend on thepath followed KEITH VAUGH
    42. 42. Properties are point functions and have exact differentials (d). 2 ∫ dV = V2 − V1 = ΔV 1Properties are point functions; but heat and workare path functions (their magnitudes depend on thepath followed KEITH VAUGH
    43. 43. Properties are point functions and have exact differentials (d). 2 ∫ dV = V2 − V1 = ΔV 1 Path functions have inexact differentials (δ) 2 ∫ δ W = W12 1Properties are point functions; but heat and workare path functions (their magnitudes depend on thepath followed KEITH VAUGH
    44. 44. ELECTRICAL WORK }Electrical power in terms of resistanceR, current I, and potential difference V. KEITH VAUGH
    45. 45. ELECTRICAL WORK Electrical Work We = VN }Electrical power in terms of resistanceR, current I, and potential difference V. KEITH VAUGH
    46. 46. ELECTRICAL WORK Electrical Work We = VN } Electrical Power (rate form) & We = VI (W )Electrical power in terms of resistanceR, current I, and potential difference V. KEITH VAUGH
    47. 47. ELECTRICAL WORK Electrical Work We = VN } Electrical Power (rate form) & We = VI (W ) When potential difference and current change with time & 2 We = ∫ VI dt 1 ( kJ )Electrical power in terms of resistanceR, current I, and potential difference V. KEITH VAUGH
    48. 48. ELECTRICAL WORK Electrical Work We = VN } Electrical Power (rate form) & We = VI (W ) When potential difference and current change with time & 2 We = ∫ VI dt 1 ( kJ )Electrical power in terms of resistanceR, current I, and potential difference V. When potential difference and current remain constant We = VI Δt ( kJ ) KEITH VAUGH
    49. 49. MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist } ✓ there must be a force acting on the boundary ✓ the boundary must move The work done is proportional to the force (F) and the distance traveled (s) KEITH VAUGH
    50. 50. MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist Work = Force × Distance We = VI Δt ( kJ ) } ✓ there must be a force acting on the boundary ✓ the boundary must move The work done is proportional to the force (F) and the distance traveled (s) KEITH VAUGH
    51. 51. MECHANICAL FORMS OF WORK There are two requirements for a work interaction between a system and its surroundings to exist Work = Force × Distance We = VI Δt ( kJ ) } ✓ there must be a force acting on When force is not constant the boundary ✓ the boundary must move & 2 We = ∫ VI dt ( kJ ) 1 The work done is proportional to the force (F) and the distance traveled (s) KEITH VAUGH
    52. 52. KEITH VAUGH
    53. 53. Shaft work is proportional to the torque applied and the number of revolutions of the shaft KEITH VAUGH
    54. 54. A force (F) acting through a momentarm (r) generates a torque (T) T T = Fr → F = r Shaft work is proportional to the torque applied and the number of revolutions of the shaft KEITH VAUGH
    55. 55. A force (F) acting through a momentarm (r) generates a torque (T) T T = Fr → F = rThis force acts through a distance (s) s = ( 2π r ) n Shaft work is proportional to the torque applied and the number of revolutions of the shaft KEITH VAUGH
    56. 56. A force (F) acting through a momentarm (r) generates a torque (T) T T = Fr → F = rThis force acts through a distance (s) s = ( 2π r ) nShaft work Shaft work is proportional to the torque applied and the number of revolutions ⎛ T ⎞ of the shaft Wsh = Fs = ⎜ ⎟ ( 2π rn ) = 2π nT ( kJ ) ⎝ r ⎠ KEITH VAUGH
    57. 57. A force (F) acting through a momentarm (r) generates a torque (T) T T = Fr → F = rThis force acts through a distance (s) s = ( 2π r ) nShaft work Shaft work is proportional to the torque applied and the number of revolutions ⎛ T ⎞ of the shaft Wsh = Fs = ⎜ ⎟ ( 2π rn ) = 2π nT ( kJ ) ⎝ r ⎠The power transmitted through the shaftis the shaft work done per unit time & & Wsh = 2π nT ( kW ) KEITH VAUGH
    58. 58. KEITH VAUGH
    59. 59. Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work done is δ Wspring = Fdx Elongation of a spring under the influence of a force KEITH VAUGH
    60. 60. Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work done is δ Wspring = FdxFor linear elastic springs, the displacement (x)is proportional to the force applied F = kx ( kN ) k: spring constant (kN/m) Elongation of a spring under the influence of a force KEITH VAUGH
    61. 61. Spring WorkWhen the length of the spring changes by adifferential amount dx under the influence of aforce (F), the work done is δ Wspring = FdxFor linear elastic springs, the displacement (x)is proportional to the force applied F = kx ( kN ) k: spring constant (kN/m)Substituting and integrating yields 1 Wspring 2 ( = k x2 − x12 2 ) ( kJ ) Elongation of a spring under the influence of a force x1 and x2: the initial and the final displacements KEITH VAUGH
    62. 62. KEITH VAUGH
    63. 63. Work done on Elastic Solid Bars 2 2 Welastic = ∫ F dx = ∫ σ n A dx 1 1 ( kJ ) Solid bars behave as springs under the influence of a force KEITH VAUGH
    64. 64. Work done on Elastic Solid Bars 2 2 Welastic = ∫ F dx = ∫ σ n A dx 1 1 ( kJ ) Solid bars behave as springs under the influence of a force Work associated with the stretching of a liquid film 2 Wsurface = ∫ σ s dA 1 ( kJ ) Stretching a liquid film with a movable wire KEITH VAUGH
    65. 65. KEITH VAUGH
    66. 66. Work done to raise or to accelerate a bodyThe work transfer needed to raise a body isequal to the change in the potential energy ofthe body.The work transfer needed to accelerate a bodyis equal to the change in the kinetic energy ofthe body. The energy transferred to a body while being raised is equal to the change in its potential energy KEITH VAUGH
    67. 67. Non-mechanical forms of workElectrical workThe generalised force is the voltage (the electricalpotential) and the generalised displacement is theelectrical charge.Magnetic workThe generalised force is the magnetic field strengthand the generalised displacement is the totalmagnetic dipole moment.Electrical polarisation workThe generalised force is the electric field strengthand the generalised displacement is the polarisationof the medium. KEITH VAUGH
    68. 68. FIRST LAW OF THERMODYNAMICS The first law of thermodynamics (the conservation of energy principle) provides a sound basis for studying the relationships among the various forms of energy and energy interactions. } The first law states that energy can be neither created nor destroyed during a process; it can only change forms. KEITH VAUGH
    69. 69. FIRST LAW OF THERMODYNAMICS The first law of thermodynamics (the conservation of energy principle) provides a sound basis for studying the relationships among the various forms of energy and energy interactions. } The first law states that energy can be neither created nor destroyed during a process; it can only change forms. Energy cannot be created or destroyed; it can only change forms KEITH VAUGH
    70. 70. The First LawFor all adiabatic processes between two specifiedstates of a closed system, the net work done is thesame regardless of the nature of the closed systemand the details of the process. KEITH VAUGH
    71. 71. KEITH VAUGH
    72. 72. In the absence of any workinteractions, the energy change ofa system is equal to the net heattransfer KEITH VAUGH
    73. 73. In the absence of any work The work (electrical) done on aninteractions, the energy change of adiabatic system is equal to thea system is equal to the net heat increase in the energy of thetransfer system KEITH VAUGH
    74. 74. ENERGY BALANCE } KEITH VAUGH
    75. 75. ENERGY BALANCEThe net change (increase or decrease) in the total energy of thesystem during a process is equal to the difference between thetotal energy entering and the total energy leaving the system }during that process. KEITH VAUGH
    76. 76. ENERGY BALANCE The net change (increase or decrease) in the total energy of the system during a process is equal to the difference between the total energy entering and the total energy leaving the system } during that process.⎛ Total energy ⎞ ⎛ Total energy ⎞ ⎛ Change in the total ⎞⎜ entering the system ⎟ − ⎜ leaving the system ⎟ = ⎜ energy of the system ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠ KEITH VAUGH
    77. 77. ENERGY BALANCE The net change (increase or decrease) in the total energy of the system during a process is equal to the difference between the total energy entering and the total energy leaving the system } during that process.⎛ Total energy ⎞ ⎛ Total energy ⎞ ⎛ Change in the total ⎞⎜ entering the system ⎟ − ⎜ leaving the system ⎟ = ⎜ energy of the system ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠ Ein − Eout = ΔEsystem KEITH VAUGH
    78. 78. KEITH VAUGH
    79. 79. The work (boundary) done on anadiabatic system is equal to theincrease in the energy of thesystem KEITH VAUGH
    80. 80. The work (boundary) done on an The energy change of a systemadiabatic system is equal to the during a process is equal to the netincrease in the energy of the work and heat transfer betweensystem the system and its surroundings KEITH VAUGH
    81. 81. Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state KEITH VAUGH
    82. 82. Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state ΔEsystem = E final = Einitial = E2 − E1 KEITH VAUGH
    83. 83. Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state ΔEsystem = E final = Einitial = E2 − E1 ΔE = ΔU + ΔKE + ΔPE KEITH VAUGH
    84. 84. Energy change of a system, ΔEsystemEnergy change = Energy at final state - Energy at initial state ΔEsystem = E final = Einitial = E2 − E1 ΔE = ΔU + ΔKE + ΔPEInternal, kinetic and potential energy changes ΔU = m ( u2 − u1 ) 1 ( ΔKE = m V22 − V12 2 ) ΔPE = mg ( z2 − z1 ) KEITH VAUGH
    85. 85. Mechanisms of Energy Transfer, Ein and EoutEnergy can be transferred to or from a system in three forms ✓ Heat transfer ✓ Work transfer ✓ Mass flow KEITH VAUGH
    86. 86. Mechanisms of Energy Transfer, Ein and EoutEnergy can be transferred to or from a system in three forms ✓ Heat transfer ✓ Work transfer ✓ Mass flow } The energy content of a control volume can be changed by mass flow as well as heat and work interactions KEITH VAUGH
    87. 87. Mechanisms of Energy Transfer, Ein and Eout Energy can be transferred to or from a system in three forms ✓ Heat transfer ✓ Work transfer ✓ Mass flow } The energy content of a control volume can be changed by mass flow as well as heat and work interactions Ein − Eout = (Qin − Qout ) + (Win − Wout ) + ( Emass, in − Emass, out ) = ΔEsystem ( kJ ) 14 2 4 3 123 Net energy transfer Change in internal, kinetic,by heat, work and mass potential, etc... energies KEITH VAUGH
    88. 88. Mechanisms of Energy Transfer, Ein and Eout Energy can be transferred to or from a system in three forms ✓ Heat transfer ✓ Work transfer ✓ Mass flow } The energy content of a control volume can be changed by mass flow as well as heat and work interactions Ein − Eout = (Qin − Qout ) + (Win − Wout ) + ( Emass, in − Emass, out ) = ΔEsystem ( kJ ) 14 2 4 3 123 Net energy transfer Change in internal, kinetic,by heat, work and mass potential, etc... energies Expressed in the Rate form dEsystem & Q = QΔt & & Ein − Eout = ( kW ) 14 2 4 3 dt & W = W ΔtRate of net energy transfer 123 by heat, work and mass Rate of change in internal, kinetic, potential, etc... energies ⎛ dE ⎞ ΔE = ⎜ ⎟ Δt ⎝ dt ⎠ KEITH VAUGH
    89. 89. The energy balance can be expressed in a per unit mass basis ein − eout = Δesystem ( kg) kJ KEITH VAUGH
    90. 90. The energy balance can be expressed in a per unit mass basis ein − eout = Δesystem ( kg) kJThe energy balance can also be expressed in a differential form KEITH VAUGH
    91. 91. The energy balance can be expressed in a per unit mass basis ein − eout = Δesystem ( kg) kJThe energy balance can also be expressed in a differential form δ Ein − δ Eout = dEsystem or δ ein − δ eout = desystem KEITH VAUGH
    92. 92. The energy balance can be expressed in a per unit mass basis ein − eout = Δesystem ( kg) kJThe energy balance can also be expressed in a differential form δ Ein − δ Eout = dEsystem or δ ein − δ eout = desystemFor a closed system undergoing a cycle, the initialand final states are identical, then the energy balancefor a cycle simplifies to Ein = EoutThe energy balance for a cycle can be expressed interms of heat and work interactions KEITH VAUGH
    93. 93. The energy balance can be expressed in a per unit mass basis ein − eout = Δesystem ( kg) kJThe energy balance can also be expressed in a differential form δ Ein − δ Eout = dEsystem or δ ein − δ eout = desystemFor a closed system undergoing a cycle, the initial For a cycle ΔE = 0and final states are identical, then the energy balance thus Q = Wfor a cycle simplifies to Ein = EoutThe energy balance for a cycle can be expressed interms of heat and work interactions & & Wnet , out = Qnet , in or Wnet , out = Qnet , in for a cycle KEITH VAUGH
    94. 94. ENERGY CONVERSION EFFICIENCIESEfficiencyis one of the most frequently used terms in thermodynamics,and it indicates how well an energy conversion or transferprocess is accomplished } Desired output Performance = Required output KEITH VAUGH
    95. 95. ENERGY CONVERSION EFFICIENCIESEfficiencyis one of the most frequently used terms in thermodynamics,and it indicates how well an energy conversion or transferprocess is accomplished } Desired output Performance = Required outputEfficiency of a water heaterThe ratio of the energy delivered to the house by hot water tothe energy supplied to the water heater. KEITH VAUGH
    96. 96. Q Amount of heat released during combustionηcombustion = = HV Heating value of the fuel burnedHeating value of the fuelThe amount of heat released when a unit amount of fuel atroom temperature is completely burned and thecombustion products are cooled to the room temperature.Lower heating value (LHV)When the water leaves as a vapour.Higher heating value (HHV)When the water in the combustion gases is completelycondensed and thus the heat of vaporisation is alsorecovered. KEITH VAUGH
    97. 97. The efficiency of space heating systems of residential and commercial buildings is usually expressed in terms of the annual fuel utilisation efficiency (AFUE). This accounts for the combustion efficiency as well as other losses such as heat losses to unheated areas and start-up and cool down losses.The definition of the heating value of gasoline KEITH VAUGH
    98. 98. GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical power output to the mechanicalpower input.Thermal efficiency of a power plantThe ratio of the net electrical power output to the rate of fuelenergy input. KEITH VAUGH
    99. 99. GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical power output to the mechanicalpower input.Thermal efficiency of a power plantThe ratio of the net electrical power output to the rate of fuelenergy input. & Wnet , electric Overall efficiency ηoverall = ηcombustionηthermalηgenerator = HHV × mnet & of a power plant KEITH VAUGH
    100. 100. GeneratorA device that converts mechanical energy to electrical energy.Generator efficiencyThe ratio of the electrical power output to the mechanicalpower input.Thermal efficiency of a power plantThe ratio of the net electrical power output to the rate of fuelenergy input. & Wnet , electric Overall efficiency ηoverall = ηcombustionηthermalηgenerator = HHV × mnet & of a power plantLighting efficiencyThe amount of light output in lumens per W of electricityconsumed. (refer to text page 88) KEITH VAUGH
    101. 101. Using energy-efficient appliances conserve energy.It helps the environment by reducing the amount ofpollutants emitted to the atmosphere during the combustionof fuelThe combustion of fuel produces ✓ carbon dioxide, causes global warming ✓ nitrogen oxides and hydrocarbons, cause smog ✓ carbon monoxide, toxic ✓ sulphur dioxide, causes acid rain The efficiency of a cooking appliance represents the fraction of the energy supplied to the appliance that is transferred to the food KEITH VAUGH
    102. 102. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, in KEITH VAUGH
    103. 103. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, inThe effectiveness of the conversion process between the mechanicalwork supplied or extracted and the mechanical energy of the fluid isexpressed by the pump efficiency and turbine efficiency, KEITH VAUGH
    104. 104. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, inThe effectiveness of the conversion process between the mechanicalwork supplied or extracted and the mechanical energy of the fluid isexpressed by the pump efficiency and turbine efficiency, & & Mechanical energy increase of the fluid ΔEmech, fluid W pump, u η pump = = = Mechanical energy input & , in Wshaft & W pump KEITH VAUGH
    105. 105. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, inThe effectiveness of the conversion process between the mechanicalwork supplied or extracted and the mechanical energy of the fluid isexpressed by the pump efficiency and turbine efficiency, & & Mechanical energy increase of the fluid ΔEmech, fluid W pump, u η pump = = = Mechanical energy input & , in Wshaft & W pump & & & ΔEmech, fluid = Emech, out − Emech, in KEITH VAUGH
    106. 106. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, inThe effectiveness of the conversion process between the mechanicalwork supplied or extracted and the mechanical energy of the fluid isexpressed by the pump efficiency and turbine efficiency, & & Mechanical energy increase of the fluid ΔEmech, fluid W pump, u η pump = = = Mechanical energy input & , in Wshaft & W pump & & & ΔEmech, fluid = Emech, out − Emech, in Mechanical energy output & Wshaft , out & Wturbine ηturbine = = = & & Mechanical energy decrease of the fluid ΔEmech, fluid Wturbine, e KEITH VAUGH
    107. 107. Efficiencies of mechanical and electrical devices Mechanical energy output Emech, out Emech, loss ηmech = = = 1− Mechanical energy input Emech, in Emech, inThe effectiveness of the conversion process between the mechanicalwork supplied or extracted and the mechanical energy of the fluid isexpressed by the pump efficiency and turbine efficiency, & & Mechanical energy increase of the fluid ΔEmech, fluid W pump, u η pump = = = Mechanical energy input & , in Wshaft & W pump & & & ΔEmech, fluid = Emech, out − Emech, in Mechanical energy output & Wshaft , out & Wturbine ηturbine = = = & & Mechanical energy decrease of the fluid ΔEmech, fluid Wturbine, e & & & ΔEmech, fluid = Emech, in − Emech, out KEITH VAUGH
    108. 108. The mechanical efficiency of a fan is the ratioof the kinetic energy of air at the fan exit tothe mechanical power input KEITH VAUGH
    109. 109. & ⎛ mV22 ⎞ & ΔEmech, fluid ⎜ ⎝ 2 ⎟ ⎠ ηmech, fan = = & Wshaft , in & Wshaft , inThe mechanical efficiency of a fan is the ratioof the kinetic energy of air at the fan exit tothe mechanical power input KEITH VAUGH
    110. 110. & ⎛ mV22 ⎞ & ΔEmech, fluid ⎜ ⎝ 2 ⎟ ⎠ ηmech, fan = = & Wshaft , in & Wshaft , in ⎝( ⎛ 0.50 kg )( 2 m ⎞ s 12 s ⎠ ) ηmech, fan = 2 50WThe mechanical efficiency of a fan is the ratioof the kinetic energy of air at the fan exit tothe mechanical power input KEITH VAUGH
    111. 111. & ⎛ mV22 ⎞ & ΔEmech, fluid ⎜ ⎝ 2 ⎟ ⎠ ηmech, fan = = & Wshaft , in & Wshaft , in ⎝( ⎛ 0.50 kg )( 2 m ⎞ s 12 s ⎠ ) ηmech, fan = 2 50WThe mechanical efficiency of a fan is the ratioof the kinetic energy of air at the fan exit to ηmech, fan = 0.72 or 72%the mechanical power input KEITH VAUGH
    112. 112. & Mechanical power output Wshaft , outηmotor = = Pump efficiency Electric power input & Welect , in & Electrical power output Welect , outηgenerator = = Generator efficiency & Mechanical power input Wshaft , in & & W pump, u ΔEmech, fluid Pump-motorη pump−motor = η pumpηmotor = = & Welect , in & Welect , in overall efficiency & Welect , out & Welect , out Turbine-generatorηturbine−gen = ηturbineηgenerator = = & & Wturbine, e ΔEmech, fluid overall efficiency KEITH VAUGH
    113. 113. Forms of energyEnergy transfer by heatEnergy transfer by workMechanical forms of workThe first law of thermodynamics  Energy balance  Energy change of a system  Mechanisms of energy transfer (heat, work, mass flow)Energy conversion efficiencies  Efficiencies of mechanical and electrical devices (turbines, pumps, etc...)Energy and environment  Ozone and smog  Acid rain  The Greenhouse effect - Global warming KEITH VAUGH
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