ENGR 3160 Fluid Mechanics
McCord, Summer 2016
July 19, 2016
ENGR 3160
EXAM #2
McCord
This exam is a sixty-minute exam. The exam is closed book. You may use two
“crib” sheets, front side of paper only, along with the exam itself. You are on your
honor not to consult with your classmates. PLEASE SHOW YOUR WORK!!!! I
CANNOT GIVE CREDIT FOR ANSWERS WITH NO SUPPORTING WORK!
Honor Pledge
On my honor, I pledge that I have neither given nor received inappropriate aid in the
preparation of this examination.
_____________________
Printed Name
Problem No.
1
2
3
Total
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Signature
Percentage of Total
40%
30%
30%
100%
1
Score
ENGR 3160
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McCord
Short Answer/Multiple Choice (40 points)
Please show your work if possible.
a. (5 points)
Multiple Choice (circle one):
In the derivation of the Bernoulli equation, what is assumed to be negligible?
i. Pressure differences
ii. Mass
iii. Viscosity
iv. Streamlines
b. (5 points)
Multiple Choice (circle one):
A steady, frictionless flow of air at 20 °C, atmospheric pressure enters a
perfectly insulated circular duct at a velocity of 10 m/s. The duct diameter
increases in the direction of flow as shown below. As the air flows through the
duct, the ENERGY:
i. Increases
ii. Remains the same
iii. Decreases
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(Continued)
c. (10 points)
Multiple Choice (circle one):
Water flows horizontally through a pipe and enters a section where the crosssectional area is larger. The velocity profile is uniform in sections 1 and 2.
V1 p1
V 2 p2
Flow
The correct statement about the static pressure p2 relative to p1 and the
velocity V2 relative to the velocity V1 along the streamline down the center of
the pipe is:
i. p2 < p1 and V2 < V1
ii. p2 < p1 and V2 > V1
iii. p2 > p1 and V2 < V1
iv. p2 > p1 and V2 > V1
v. Not enough information to determine
d. (10 Points) – Calculate.
Given the velocity vector field:
𝑉̃ = 3𝑡𝑖̂ + 𝑥𝑧𝑗̂ + 𝑡𝑦 2 𝑘̂
Find the component for the acceleration in the x direction only.
Please SHOW YOUR WORK!
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(Continued)
e. (5 points)
Multiple Choice (circle one)
A fluid flows steadily through a pipe with a uniform cross-sectional area. The
density of the fluid increases to twice its initial value as it flows through the pipe.
The correct statement about the average velocity V in the pipe is:
Flow
ρ1
ρ2 = 2*ρ1
V2
V1
i.
ii.
iii.
iv.
v.
V2 = 2*V1
V2 = V1/2
V2 = V1
V2 = V1/4
V2 = 4*V1
f. (5 points)
Multiple Choice (circle one)
Water flows steadily in and out of the system shown below in four different
pipes. The mass flow rate in three of these pipes is shown. What is the mass
flow rate in the fourth pipe?
3 kg/s
5 kg/s
𝑚̇
System
4 kg/s
i.
ii.
iii.
iv.
v.
12 kg/s
9 kg/s
7 kg/s
4 kg/s
3 kg/s
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(30 points) Please show your work!
The horizontal wye fitting shown below splits the water flow (Q) equally. If the
volumetric flow rate Q1 = 5 ft3/s and p1 = 25 lb/in2 (gage pressure), find:
a) p2
b) p3
c) Vector force to hold the wye fitting in place
Neglect losses. (ρ = 1.94 slugs/ft3, γ = 62.4 lb/ft3)
D2=3 in
1
30°
2
Water
D1=6 in
½ Q1
Q1
3
50°
5
D3=4 in
ENGR 3160
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McCord
(30 points) Please show your work!
In the figure shown below, the connecting round pipe is commercial steel which is 6 cm
in diameter. The fluid is water (ρ = 998 kg/m3, μ = 0.001 kg/m·s). For commercial steel,
take the roughness height ε = 0.046 mm.
Open to atmosphere
200 kPa Gage
15 m
L = 50 m
a) Which way does the flow go? Left to right or right to left?
b) Estimate the flow rate, in m3/h. Consider major losses due to pipe friction but not
minor ones.
c) In your calculations of friction factor, please iterate one time to get a closer
answer. Multiple iterations are not required or desired on the exam due to lack of
time! Make assumptions!
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(Left blank for your work)
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