FE Thermodynamics Review

1
FE ThermodynamicsReview

• Dr. Omar Meza
• Assistant Professor
• Department of Mechanical Engineering

2
Topics covered

• Thermodynamics Law
• 1st and 2nd law
• Energy , heat and work
• Availability and reversibility
• Cycles
• Ideal gases
• Mixture of gases
• Phase change
• Heat Transfer
• Properties of
• enthalpy

3
Tips for taking exam

• Use the reference handbook
• Know what it contains
• Know what types of problems you can use it for
• Know how to use it to solve problems
• Refer to it frequently
• Work backwards when possible
• FE exam is multiple choice with single correct
  answer
• Plug answers into problem when it is convenient
  to do so
• Try to work backwards to confirm your solution as
  often as possible
• Progress from easiest to hardest problem
• Same number of points per problem
• Calculator tips
• Check the NCEES website to confirm your model is
  allowed
• Avoid using it to save time!
• Many answers do not require a calculator
  (fractions vs. decimals)

4
Properties of Single-Component Systems
For a simple substance, specification of any two
intensive, independent properties is sufficient
to fix all the rest.
Handbook page
5
Properties of Single-Component Systems
A substance that has a fixed chemical composition
throughout is called a pure substance.
Handbook page
6
Properties of Single-Component Systems

• A substance whose properties are uniform
  throughout is referred to as
• A solid
• An ideal substance
• A pure substance
• A standard substance

• A substance whose properties are uniform
  throughout is referred to as
• A solid
• An ideal substance
• A pure substance
• A standard substance

7
Properties of Single-Component Systems
8
Properties of Single-Component Systems

• Given Steam at 2.0 kPa is saturated at 17.5 oC.
  In what state will the steam be at 40 oC if the
  pressure is 2.0 kPa?

T 40oC
Tsat 17.5oC

• Analysis
• _at_ P 2.0 kPa, Tsat 17.5oC
• Tsat lt T ? superheated vapor

9
Properties of Single-Component Systems
10
Properties of Single-Component Systems

• Find the volume occupied by 20 kg of steam at 0.4
  MPa, 400oC

• At 0.4 MPa the Tsat142oC approximately. It means
  that the steam is in the superheated region

11
Properties of Single-Component Systems
Real gases exhibit ideal-gas behavior at
relatively low pressures and high temperatures.
Handbook page
12
Properties of Single-Component Systems

• All real gases deviate somewhat from ideal gas
  behavior PV mRT. For which of the following
  conditions is the deviation the smallest?
• High temperature and low volume
• High temperature and low pressures
• High pressures and low volumes
• High pressure and low temperatures

• When the volume of an ideal gas is doubled while
  the temperature is halved, what happens to the
  pressure?
• Pressure is doubled
• Pressure is halved
• Pressure is quartered
• Pressure is quadrupled

13
Properties of Single-Component Systems
Handbook page
14
Properties of Single-Component Systems
15
Properties of Single-Component Systems
16
First Law of Thermodynamics
Handbook page
17
First Law of Thermodynamics
Formal sign convention 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 negative.
Wb is positive ? for expansion Wb is negative ?
for compression
Handbook page
18
First Law of Thermodynamics
19
First Law of Thermodynamics

• During a process, 30J of work are done by a
  closed stationary system on its surroundings. The
  internal energy of the system decreases by 40 j.
  What is the heat transfer?

20
First Law of Thermodynamics
Handbook page
21
First Law of Thermodynamics

• Calculate the work done by a piston contained
  within a cylinder with air if 2m3 is tripled
  while the temperature is maintained at a constant
  T 30oC. The initial pressure is P1400 kPa
  absolute.

22
First Law of Thermodynamics
Polytropic process in a closed system
23
First Law of Thermodynamics
Handbook page
24
First Law of Thermodynamics
Handbook page
25
First Law of Thermodynamics
26
First Law of Thermodynamics
27
First Law of Thermodynamics
Handbook page
28
First Law of Thermodynamics
Handbook page
29
First Law of Thermodynamics
Handbook page
30
First Law of Thermodynamics

• A steam coil operating at steady state receives
  30 kg/min of steam with an enthalpy of 2900
  kJ/kg. if the steam leaves with an enthalpy of
  1600 kJ/min, what is the rate of heat transfer
  from the coil?

31
First Law of Thermodynamics
32
First Law of Thermodynamics
33
Basic Cycles
34
Basic Cycles
35
Basic Cycles
36
Basic Cycles
Handbook page
37
Basic Cycles
38
Basic Cycles
39
Basic Cycles
40
Basic Cycles
41
Basic Cycles
42
Basic Cycles
43
Basic Cycles
44
Basic Cycles
45
Basic Cycles
46
Basic Cycles
47
Basic Cycles
48
Basic Cycles
49
Basic Cycles
50
Basic Cycles
51
Basic Cycles
52
Basic Cycles
53
Basic Cycles
54
Ideal Gas Mixture
Handbook page
55
Ideal Gas Mixture
56
Ideal Gas Mixture
57
Ideal Gas Mixture
58
Psychrometrics
Handbook page
59
Psychrometrics
Mollier Diagram
Handbook page
60
Psychrometrics
61
Psychrometrics
62
Psychrometrics
63
Psychrometrics
64
Psychrometrics
65
Psychrometrics
66
Psychrometrics
67
Psychrometrics
68
Psychrometrics
69
Combustion Processes
70
Combustion Processes
71
Combustion Processes
72
Combustion Processes
73
Combustion Processes
74
Second Law of Thermodynamics
Handbook page
75
Second Law of Thermodynamics
Part of the heat received by a heat engine is
converted to work, while the rest is rejected to
a sink.

• This is a law.
• It is always observed in real heat engines.
• One cannot derive it from first principles.
• No exceptions are known.

It is not just that we havent looked hard
enough and that future discoveries will make it
possible to convert heat completely to work.
76
Second Law of Thermodynamics
77
Second Law of Thermodynamics
The efficiency of a refrigerator is expressed in
terms of the coefficient of performance (COP).
The objective of a refrigerator is to remove
heat (QL) from the refrigerated space.
Can the value of COPR be greater than unity?
78
Second Law of Thermodynamics
The work supplied to a heat pump is used to
extract energy from the cold outdoors and carry
it into the warm indoors.
for fixed values of QL and QH
79
Second Law of Thermodynamics

1. 1500-MW
2. 600-MW
3. 900-MW
4. 2100-MW

80
Second Law of Thermodynamics

1. Yes
2. No
3. Not clear
4. NA

81
Entropy
82
Entropy

1. 2.82 kJ/K
2. 6.86 kJ/K
3. -8.10 kJ/K
4. 8.10 kJ/K

83
Preguntas? Comentarios?
84
Muchas Gracias !