Lecture 2 Applied theermo very important

Lecture of Applied Physics

1. IDE-314
Applied Thermodynamics
Lecture 2
Engr. Muhammad Ebrahem Khalid
Electrical Engineering Department

2. 2
Review
Last Lecture
•Pressure
▪Variation of Pressure with depth
▪Pressure Measurement
Today’s Lecture
•Forms of Energy

3. Key to Understanding Thermodynamics
•Understand ENERGY and its’:
•Forms and types
•Transfer
•Transformation
•Interactions with a system
•Modes of transfer between System and Surroundings
•Effects caused by transfer
7/7/2024 3

4. Introduction
4
We are familiar with
conservation of energy principle
(1
st
law of thermodynamics)
“Energy cannot be created or
destroyed it can only change
from one form to another”
This seems simple but let us test
ourselves

5. Test your
understanding
•Consider a well insulated room
•A room refrigerator with door open
•You may use a fan to maintain temp uniformity
•Now what you think the temp of room, inc., dec. or
const.
The conservation of energy requires that content of energy incr.
equal to the amount of elect. energy drawn by the refrigerator

6. THERMODYNAMIC VIEWPOINT OF ENERGY
Energy
Macroscopic Microscopic

7. THERMODYNAMIC VIEWPOINT OF ENERGY
Energy
Macroscopic Microscopic
Kinetic
Potential

8. FORMS OF ENERGY
•Total energy (E): Sum of all forms of energy related to system. Consists of TWO groups:
•Macroscopic: System possesses as a whole w.r.t. some outside frame e.g. KE, PE. Relates to
motion, gravity, magnetism, electricity etc.
•Microscopic: Independent of outside reference frame. Relates to:
•Molecular structure of system
•Degree of molecular activity
•Can be viewed as KE and PE of molecules
8

9. Macroscopic Energy
•Kinetic Energy (KE)
•KE = mV
2
/2
•ke = V
2
/2
•Potential Energy (PE)
•PE = mgz
•pe = gz
7/7/2024 9
The macroscopic energy of a system is related to motion and
the influence of some external effects such as gravity,
magnetism, electricity, and surface tension.

11. 12
THERMODYNAMIC VIEWPOINT OF ENERGY
Energy
Macroscopic Microscopic
InternalKinetic
Potential Sensible Latent
Chemical Nuclear

12. Microscopic
Energy
7/7/2024 13
Kinetic energy of individual molecules
Potential energy of individual molecules
Binding forces
•Chemical Energy
•Nuclear Energy etc.
Lump them all together into what we call
internal energy (U)

13. INTERNAL ENERGY
• Internal energy of a system consists of:
•Sensible Energy: associated with KE of molecules
[Temperature, Pressure]
•Latent energy: associated with binding forces between
molecules, atoms and particles of a substance
•Chemical energy: associated with atomic bonds in
molecules
•Nuclear energy: due to strong bond within nucleus of atom
itself
14

14. Sensible Heat
•Portion of internal energy of system associated with KE of the
molecules is called sensible heat
•On molecular level it includes:
•Translational energy
•Rotational KE
•Vibrational
•Spin energy
15

15. THERMODYNAMIC VIEWPOINT OF ENERGY
Energy
Macroscopic MicroscopiccMicroscopicMacroscopiE +=

16. THERMODYNAMIC VIEWPOINT OF ENERGY
Energy
Macroscopic Microscopic
InternalKinetic
PotentialUPEKEE ++= UmgzmVE ++=
2
2
1

17. 7/7/2024 18
A unit mass basis is often more convenient
•Total Energy: e = E/m
•Internal Energy: u = U/m
•Kinetic Energy: ke = KE/m = V
2
/2
•Potential Energy: pe = PE/m = gz
Thus on unit mass basis:

18. HOW ENERGY
IS
TRANFERED?
7/7/2024 23
Across Close System through:
Heat Transfer
Work Interaction
Across Open System through:
Heat Transfer
Work Interaction
Mass Transfer

19. MODES OF
ENERGY
TRANSFER
7/7/2024 24
Heat Transfer: driving force is
temperature difference
Work: an interaction when
temperature difference is not the
driving force
Mass Transfer: mass flow into or out
of system

20. 7/7/2024 25
How does energy cross the system boundary
of closed system?
•Heat
•Work
Q W
System

21. THERMODYNAMIC
LAWS
7/7/2024 26
Zeroth Law talks of thermal equilibrium
First Law
•An expression of conservation of energy
principle
•Energy is a thermodynamic property
Second Law
•Energy has quality as well as quantity
•Process occur in the direction of decreasing
quality of energy

22. Heat
A form of energy associated
with the motion of atoms or
molecules.
Transferred from higher
temperature objects to
objects at a lower
temperature.

23. 28
Heat Transfer
⚫Heat is defined as the form of energy that is transferred
between two systems (or a system and its surroundings) by
virtue of a temperature difference.
⚫Heat is energy transition – recognized only while crossing
boundary of a system.
⚫In thermodynamics, the term heat simply means heat
transfer.
•The larger the temperature
difference, the higher is the
rate of heat transfer.
•The transferred heat
becomes part of the
internal energy of the
system.

24. Heat transfer
29
•A process during which there is no heat
transfer is called an adiabatic process.
•The system is well insulated so that only a
negligible amount of heat can pass
through the boundary.
•Although no heat transfer during
adiabatic process, the energy content and
thus the temperature of a system can still
be changed by others means such as
work.

25. Symbols
Q
Total heat transferred
kJ or BTU
q
Heat/mass
kJ/kg or BTU/lb
m

Rate of heat transfer
kJ/sec = kW
7/7/2024 30

26. Heat : Sign
Convention
Heat transferred into a
system is positive
Heat transferred out of a
system is negative
7/7/2024 31

27. Mechanism of
Heat Transfer
32
•Three different ways
•Conduction, Convection, and Radiation
•All modes require the existence of
temperature difference
•All modes of heat transfer are from higher
temperature to lower temperature

28. Conduction
33
•Transfer of heat through direct contact.
•Occurs anytime objects at different
temperatures are touching each other.
•As long as the objects are in contact, transfer
of heat will continue until the temperature of the
objects is the same.
•From more energetic particle to less energetic
one as a result of interactions between
particles

29. Convection
•The transfer of energy in a liquid or gas.
•When part of a gas or liquid is heated,
the particles it is made up of move faster
and spread out more.
•The moving particles bump into other
particles, causing them to move faster
and spread out more.

30. Radiation
•Energy transferred in the form of rays or
waves or particles.
•We will concentrate on the type of
radiation that travels as electromagnetic
waves.

31. Summary

32. Energy Transfer by
Work
37

33. Work
Work is the energy transferred with force acting through a distance
7/7/2024 38

34. 7/7/2024 39
Work
 W = Fd
[N m] = [J] usually we’ll use [kJ]
 w = W/m
[kJ/kg]

[kJ/sec]
[kW]•
W

35. Work : Sign
Convention
7/7/2024 40
Work done by a
system is positive
Work done on a
system is negative

36. Let us look at
Similarities
Between Heat
and Work
41
•Both heat and work are dynamic forms of
energy
•They are recognized as they cross the
system boundary
•Systems possess energy, but not heat or
work
•Both are associated with a process, and not
with a state
•Both are path functions (i.e. their magnitude
depends on the path followed during the
process as well as end state)
•Page 63

37. Point Functions
and Path
Functions
•Properties and Energies are Point
Functions
•Define State of the system
•Part of system / stored in system
•Exact Differentials
•Energy Transfer is a Path Function
•Define process a system undergoes
•Moves system from one state to
another
•Inexact Differentials
42

38. Path
Functions
43
▪Have inexact differentials
▪???????????? ��?????? ????????????
▪Properties are point functions – they have exact
differentials
න
1
2
??????�=�
2−�
1=Δ�
▪If we want to know how much works was done, we
need to know the path
න
1
2
??????�=�
12
▪The integral of ??????� is not �
2−�
1, later is
meaningless, since work is not a property and sys do
not possess the works at a state

39. Path Functions and Point Function
7/7/2024 44

40. 7/7/2024 45
Let’s do an example on Heat and Work:
•A potato initially at room temperature is being baked in an oven that is
maintained at 200
o
C. Is there any heat transfer?
It depends on how you define your system
Example 2.2—2.6

41. If system (boundary) is interior of the oven
•No heat transfer takes place
between system and
surroundings because the oven
is insulated.
•However, electric current
(electron) crosses the boundary,
so work is done on the system
•THIS IS WORK INTERACTION
7/7/2024 46

42. If system (boundary) is
Potato
•Heat transfer takes place due to
temperature difference between system
and surroundings (around potato)
•No work in any form crosses the system
boundary
•THIS IS HEAT INTERACTION
7/7/2024 47

43. If system (boundary) is air
•This time the sys boundary will include the outer surface of
heating element and will not cut thru (no electron cross sys
boundary)
•Heat transferred from element to air due to temp difference
•THIS IS HEAT INTERACTION
•Energy transfer can be heat or work depending on how
system is selected
7/7/2024 48

44. Mechanical Forms of work
49

45. Mechanical
Forms of Work
•Some common forms of Mechanical Work are:
•Shaft work
•Gravitational work
•Acceleration work
•Spring work etc.
50

46. Work
•In physics, work has a very specific
meaning.
•In Thermodynamics (also in
physics), work represents a
measurable change in a system,
caused by a force.

47. Work
•If you push a box with a force of
one newton for a distance of one
meter, you have done exactly one
joule of work.

48. Work (force is parallel to distance)
W = F x d
Distance (m)
Force (N)
Work (joules)

49. Work (force at angle to distance)
W = Fd cos ()
Distance (m)
Force (N)
Work (joules) Angle

50. Mechanical Forms of Work
•Shaft Work:
•Energy transmission with a
rotating shaft is very common.
•For example, car, boat etc.
•Often torque applied to the shaft
is constant; so is the force!
•Lets finds out the work done
during n revolutions for a
specified constant torque (τ):r
FFr

 =→=
7/7/2024 55
A force F acting through a
moment arm r generates
a torque:

51. Mechanical Forms of Work
Shaft Work (cont’):
•The force F acts through a
distance s which is related to
radius r by:( )

nrn
r
sFW
sh
2 2 =





==
7/7/2024 56
Then the shaft work is:()nrs 2=
The power transmitted
through the shaft is:nW
sh

2= n
No. of revolutions
per unit time

52. Example

53. Example

54. Gravitational Work - Work done against
gravity
W = mgh
Height object raised (m)
Gravity (m/sec
2
)
Work (joules)
Mass (g)

56. Mechanical form of work :
acceleration work
Acceleration Work:
•It is the work associated with change
in velocity of a system.
•For a system of mass m that
accelerates from velocity V
1 to V
2, the
acceleration work is obtained from
Newton’s second law of motion:
7/7/2024 61F ma
dV
Fm
dV
dt
a
dt
→
→
=

=
=

Note that the acceleration work
is equivalent to the change in
kinetic energy of the system.Also
ds
V ds V dt
dt
→→
=  =

57. Mechanical Forms of Work
Spring Work:
•Consider a spring whose length
changes a differential amount
dx under the influence of force
F.
•The work done is:
7/7/2024 62FdxW
spring
= 
Hence the spring work
can be represented as:( )
2
1
2
2
2
1
xxkW
spring −=
For linear elastic spring,
displacement x is
proportional to force
applied:kxF=
k is spring constant

58. Non-Mechanical Forms of Work
•Electric work
•Magnetic work
•Electrical polarization work
7/7/202463

59. Electrical Work
•It was pointed out that electron crossing the system boundary - do
electrical work
•When N coulombs of electrical charge move through a potential difference
V, the electrical work done is
•Which can be expressed in rate form (power) as
•If both V and I, vary with time, work done is given by

60. Summary
65

61. Law of Conservation
of Energy
•As energy takes different forms and changes things by doing
work, nature keeps perfect track of the total.
•No new energy is created and no existing energy is destroyed.

62. Energy Balance of a System







=








−








system theofenergy
in total Change
System theLeaving
Energy Total
System theEntering
Energy Total EEE
outin =−
How can energy get into or out of a system?
Through Heat, Work and Mass Transfer!12EE−=
67
Total energy at
final state
Total energy at
initial state

63. So far…
•We’ve looked at
•Q (heat)
•W (work)
•E (Energy)
•But we have not tried to connect them
•(Though we have hinted at it!!)
•Now we establish connection among these forms of energy!
7/7/2024 68

64. First Law of Thermodynamics
•You have learnt about it while stating the following
about energy:
•Energy can neither be created nor destroyed
•It can, however, change forms
•Now consider a system having various forms of
energy interactions
7/7/2024 69
Combustion
Heat Out

65. Energy Balances of a System







=








−








system theofenergy
in total Change
System theLeaving
Energy Total
System theEntering
Energy Total EEE
outin =−
7/7/2024 70
PROCESS PROPERTY

66. ΔE (Change in Total Energy of System)
71
The change in stored energy for the system is EUKEPE=+ +
Now the conservation of energy principle, or the first law of
thermodynamics for closed systems, is written asin outE E U KE PE− =  +  + 
If the system does not move with a velocity and has no change in
elevation, it is called a stationary system, and the conservation of
energy equation reduces toin outE E U− = 

67. Mechanisms
of Energy
Transfer
E
in and E
out
72
•The mechanisms of energy transfer at a system
boundary are: Heat, Work, mass flow.
•Closed System: Only heat and work energy
transfers occur at the boundary of a closed (fixed
mass) system.
•Open systems or control volumes: energy
transfer across the control surfaces by mass flow
as well as heat and work.

68. Mechanisms of Energy Transfer E
in and E
out
73
•Energy Balance becomes
•In compact Form( )( )
( ),,
in out in out in out
mass in mass out system
E E Q Q W W
E E E
− = − + −
+ − =  Net energy transfer Change in internal, kinetic,
by heat, work, and mass potential, etc., energies
( )
in out systemE E E kJ− = 
1 4 2 43 14 2 43

69. Energy Balance
Expressed in a rate form, as  E E E kW
in out system
− =
Rate of net energy transfer
by heat, work, and mass
Rate change in internal, kinetic,
potential, etc., energies
()
 

The energy balance may be expressed on a per unit mass basis
as( / )
in out system
e e e kJ kg− = 
and in the differential forms as()
( / )
in out system
in out system
E E E kJ
e e e kJ kg
  
  
−=
−=

70. Applying Energy Balance
75
For Closed System

71. Applying Energy Balance
76
For Closed System
For Closed-Cyclic System

72. Let’s Look at
Closed
Systems first
undergoing a
Cyclic
Process
77
•The only way energy can get into or out of a
closed system is by heat or work transfer
•For the closed system undergoing cyclic process,
the First Law sates that:
•“The net heat transfer is equal to net work
done for a system undergoing a cyclic
process”
•Mathematically
????????????=????????????
ර????????????=ර??????�
7/7/2024

73. How to solve
problems
78
•Draw a picture
•List the data you know
•Identify the goal (What do you want to solve for)
•List the equations you know
•Draw a Process Diagram
•Solve for the unknowns
7/7/2024

74. Examples

75. Examples

76. Solve some
problems
7/7/2024 83
Topic : First law of
thermodynamics
Attempt following problems
from chapter 2
(2-35 ~2-49) page 100 & 101
(text)

77. Energy
Conversion
Efficiencies
7/7/2024 84
Efficiency is one of the most frequently used
terms in thermodynamics
It indicates how well an energy conversion or
transfer process is accomplished.
Efficiency is also one of the most frequently
misused terms in thermodynamics and a source
of misunderstandings.
This is because efficiency is often used without
being properly defined first

79. Energy Efficiency
86
Energy
Conversion
Device
Energy Input
Useful Energy
Output
Energy Dissipated
to the Surroundings

80. Efficiencies of Mechanical and Electrical Devices
•The transfer of mechanical energy is usually accomplished by a rotating shaft, and thus
mechanical work is often referred to as shaft work
•In the absence of any ir-reversibilities such as friction, mechanical energy can be converted
entirely from one mechanical form to another, and the mechanical efficiency of a device or
process can be defined as
7/7/2024 87

81. Efficiencies of Mechanical and Electrical Devices
•The degree of perfection of the conversion process between the
mechanical work supplied or extracted and the mechanical energy of the
fluid is expressed by the pump efficiency and turbine efficiency, defined
as
7/7/2024 88

82. Efficiencies of Mechanical and Electrical Devices
•The mechanical efficiency should not be confused with the motor
efficiency and the generator efficiency, which are defined as
7/7/202489

83. Energy Conversion Efficiencies
•The efficiency of equipment that involves the combustion of a fuel is based on the
heating value of the fuel
•Amount of heat released when a unit amount of fuel at room temperature is
completely burned and the combustion products are cooled to the room temperature
•Then the performance of combustion equipment can be characterized by
combustion efficiency, defined as
7/7/202490

84. Energy
Conversion
Efficiencies
•A generator is a device that converts
mechanical energy to electrical energy
•Generator efficiency, is the ratio of the
electrical power output to the mechanical
power input.
•The thermal efficiency of a power plant, is
the ratio of the net shaft work output of
the turbine to the heat input to the
working fluid.
91

85. Energy Conversion Efficiencies
•The effects of other factors are incorporated by defining an overall
efficiency for the power plant as the ratio of the net electrical power
output to the rate of fuel energy input
7/7/2024 92

86. Illustration
•An electric motor consumes 100 watts (a joule per second
(J/s)) of power to obtain 90 watts of mechanical power.
Determine its efficiency ?
= 90 W x 100 = 90 %
100 W
93
InputEnergyTotal
OutputEnergyUseful
Efficiency=

87. Flow Rates
94
Mass Flow Rate
Amount of mass flowing through a cross section per unit time
Volume Flow Rate
Amount of mass flowing through a cross section per unit time.

88. Problem Solving Technique
95
∆�=∆�−∆??????
��??????��=ሶ??????=ሶ��
•Solve for energy of the system using Energy
Balance
•Rate of energy transfer (power) can be calculated
using
�??????�� �� ??????�??????� ��??????�����=ሶ�=ሶ��
•Similarly rate of heat / work transfer is
�??????�� �� ??????��?????? ��??????�����=ሶ??????=ሶ�??????

89. •Thanks
•Q & A