Notes to instructors
Introduction
The following ideas and information are provided to assist the instructor in the design and implementation
of the course. Traditionally this course is taught at Washington State University and the University of Idaho as a
three-credit semester course which means 3 hours of lecture per week for 15 weeks. Basically the first 11 chapters
and Chapter 13 (Flow Measurements) are covered in Mechanical Engineering. Chapters 12 (Compressible Flow)
and Chapter 14 (Turbomachinery) may be covered depending on the time available and exposure to compressible
flow in other courses (Thermodynamics). Open channel flow (Chapter 15) is generally not covered in Mechanical
Engineering. When the text is used in Civil Engineering, Chapters 1-11 and 13 are nominally covered and Chapters
14 and 15 may be included if time permits and exposure to open channel flow may not be available in other courses.
The book can be used for 10-week quarter courses by selecting the chapters, or parts of the chapters, most appropriate
for the course.
Author Contact
Every effort has been made to insure that the solution manual is error free. If errors are found (and they
will be!) please contact Professors Crowe or Elger.
Donald Elger Clayton Crowe
Mechanical Engineering Dept School of Mechanical Eng. & Matl. Science
University of Idaho Washington State University
Moscow, ID 83844-0902 Pullman, WA 99164-2920
Phone (208) 885-7889 Phone (509) 335-3214
Fax (208) 885-9031 Fax (509) 335-4662
e-mail: e-mail:
Design and Computer Problems
Design problems (marked in the text in blue) are those problems that require engineering practices such
as estimation, making asummptions and considering realistic materials and components. These problems provide a
platform for student discussion and group activity. One approach is to divide the class into small groups of three or
four and have these groups work on the design problems together. Each group can then report on their design to
the rest of the class. The role of the professor is to help the student learn the practices of the design review—that is,
teach the student to ask in-depth questions and teach them how to develop meaningful and in-depth answers. This
dialogue stimulates interest and class discussion. Solutions to most design problems are included in the solution
manual.
Computer-oriented problems (marked in the text is blue) are those problems may best be solved using
software such as spreadsheets, TK Solver or MathCad. The choice is left to the student. The answer book also
includes the results for the computer-oriented problems.
1
,PROBLEM 2.1
Situation: An engineer needs density for an experiment with a glider.
Local temperature = 74.3 ◦ F = 296.7 K.
Local pressure = 27.3 in.-Hg = 92.45 kPa.
Find: (a) Calculate density using local conditions.
(b) Compare calculated density with the value from Table A.2, and make a recom-
mendation.
J
Properties: From Table A.2, Rair = 287 kg· K
, ρ = 1.22 kg/ m3 .
APPROACH
Apply the ideal gas law for local conditions.
ANALYSIS
a.) Ideal gas law
p
ρ =
RT
92, 450 N/ m2
=
(287 kg/ m3 ) (296.7 K)
= 1.086 kg/m3
ρ = 1.09 kg/m3 (local conditions)
b.) Table value. From Table A.2
ρ = 1.22 kg/m3 (table value)
COMMENTS
1. The density difference (local conditions versus table value) is about 12%. Most
of this difference is due to the effect of elevation on atmospheric pressure.
2. Answer ⇒ Recommendation—use the local value of density because the effects
of elevation are significant.
1
,PROBLEM 2.2
Situation: Carbon dioxide is at 300 kPa and 60o C.
Find: Density and specific weight of CO2 .
Properties: From Table A.2, RCO2 = 189 J/kg·K.
APPROACH
First, apply the ideal gas law to find density. Then, calculate specific weight using
γ = ρg.
ANALYSIS
Ideal gas law
P
ρCO2 =
RT
300, 000
=
189(60 + 273)
= 4.767 kg/m3
Specific weight
γ = ρg
Thus
γ CO2 = ρCO2 × g
= 4.767 × 9.81
= 46.764 N/m3
2
, PROBLEM 2.3
Situation: Methane is at 500 kPa and 60o C.
Find: Density and specific weight.
J
Properties: From Table A.2, RMethane = 518 kg· K
.
APPROACH
First, apply the ideal gas law to find density. Then, calculate specific weight using
γ = ρg.
ANALYSIS
Ideal gas law
P
ρHe =
RT
500, 000
=
518(60 + 273)
= 2.89 kg/m3
Specific weight
γ = ρg
Thus
γ He = ρHe × g
= 2.89 × 9.81
= 28.4 N/m3
3
Introduction
The following ideas and information are provided to assist the instructor in the design and implementation
of the course. Traditionally this course is taught at Washington State University and the University of Idaho as a
three-credit semester course which means 3 hours of lecture per week for 15 weeks. Basically the first 11 chapters
and Chapter 13 (Flow Measurements) are covered in Mechanical Engineering. Chapters 12 (Compressible Flow)
and Chapter 14 (Turbomachinery) may be covered depending on the time available and exposure to compressible
flow in other courses (Thermodynamics). Open channel flow (Chapter 15) is generally not covered in Mechanical
Engineering. When the text is used in Civil Engineering, Chapters 1-11 and 13 are nominally covered and Chapters
14 and 15 may be included if time permits and exposure to open channel flow may not be available in other courses.
The book can be used for 10-week quarter courses by selecting the chapters, or parts of the chapters, most appropriate
for the course.
Author Contact
Every effort has been made to insure that the solution manual is error free. If errors are found (and they
will be!) please contact Professors Crowe or Elger.
Donald Elger Clayton Crowe
Mechanical Engineering Dept School of Mechanical Eng. & Matl. Science
University of Idaho Washington State University
Moscow, ID 83844-0902 Pullman, WA 99164-2920
Phone (208) 885-7889 Phone (509) 335-3214
Fax (208) 885-9031 Fax (509) 335-4662
e-mail: e-mail:
Design and Computer Problems
Design problems (marked in the text in blue) are those problems that require engineering practices such
as estimation, making asummptions and considering realistic materials and components. These problems provide a
platform for student discussion and group activity. One approach is to divide the class into small groups of three or
four and have these groups work on the design problems together. Each group can then report on their design to
the rest of the class. The role of the professor is to help the student learn the practices of the design review—that is,
teach the student to ask in-depth questions and teach them how to develop meaningful and in-depth answers. This
dialogue stimulates interest and class discussion. Solutions to most design problems are included in the solution
manual.
Computer-oriented problems (marked in the text is blue) are those problems may best be solved using
software such as spreadsheets, TK Solver or MathCad. The choice is left to the student. The answer book also
includes the results for the computer-oriented problems.
1
,PROBLEM 2.1
Situation: An engineer needs density for an experiment with a glider.
Local temperature = 74.3 ◦ F = 296.7 K.
Local pressure = 27.3 in.-Hg = 92.45 kPa.
Find: (a) Calculate density using local conditions.
(b) Compare calculated density with the value from Table A.2, and make a recom-
mendation.
J
Properties: From Table A.2, Rair = 287 kg· K
, ρ = 1.22 kg/ m3 .
APPROACH
Apply the ideal gas law for local conditions.
ANALYSIS
a.) Ideal gas law
p
ρ =
RT
92, 450 N/ m2
=
(287 kg/ m3 ) (296.7 K)
= 1.086 kg/m3
ρ = 1.09 kg/m3 (local conditions)
b.) Table value. From Table A.2
ρ = 1.22 kg/m3 (table value)
COMMENTS
1. The density difference (local conditions versus table value) is about 12%. Most
of this difference is due to the effect of elevation on atmospheric pressure.
2. Answer ⇒ Recommendation—use the local value of density because the effects
of elevation are significant.
1
,PROBLEM 2.2
Situation: Carbon dioxide is at 300 kPa and 60o C.
Find: Density and specific weight of CO2 .
Properties: From Table A.2, RCO2 = 189 J/kg·K.
APPROACH
First, apply the ideal gas law to find density. Then, calculate specific weight using
γ = ρg.
ANALYSIS
Ideal gas law
P
ρCO2 =
RT
300, 000
=
189(60 + 273)
= 4.767 kg/m3
Specific weight
γ = ρg
Thus
γ CO2 = ρCO2 × g
= 4.767 × 9.81
= 46.764 N/m3
2
, PROBLEM 2.3
Situation: Methane is at 500 kPa and 60o C.
Find: Density and specific weight.
J
Properties: From Table A.2, RMethane = 518 kg· K
.
APPROACH
First, apply the ideal gas law to find density. Then, calculate specific weight using
γ = ρg.
ANALYSIS
Ideal gas law
P
ρHe =
RT
500, 000
=
518(60 + 273)
= 2.89 kg/m3
Specific weight
γ = ρg
Thus
γ He = ρHe × g
= 2.89 × 9.81
= 28.4 N/m3
3
