Name _________________________
CEE 332 Hydraulic Engineering: Prelim 1
Mar. 2, 1999 - 10:10-11:25 AM
Closed book, one 8.5” x 11” summary sheet
Note: The last page of this exam is an equation sheet!
Read each problem carefully before beginning to work on the answer!
Make sure you answer each part of each question. May the time you spent preparing for this
exam pay off.
True or False. Circle the best answer. (2 point each, total of 20 points)
1)
T or F? Axial flow pumps should be started with the downstream valve closed to
minimize initial motor load.
2)
T or F? Major frictional losses are independent of pressure.
3)
T or F? Major frictional losses are independent of pipe length.
4)
T or F? The Swamee-Jain equation can be derived based on conservation of mass,
momentum, and energy.
5)
T or F? Eliminating the vena contracta in a pipe contraction will increase the contraction
minor loss.
6)
T or F? The Darcy-Weisbach equation can be used for fluids other than water.
7)
T or F? Smooth pipes have no major head loss.
8)
T or F? Kinetic energy is converted into potential energy after fluid leaves a pump
impeller.
9)
T or F? Steel pipe should be used inside a peristaltic pump.
Multiple Choice, Pick the BEST answer (3 points each, total of 15 points)
1) Which flow meter is most commonly used in households and businesses?
a) Elbow meter
b) Electromagnetic flow meter
c) Displacement meter
d) Vortex Meter
2) Which of the following pumps do not need to be primed?
a) Axial flow pump
b) Radial flow pump
c) Jet pump
d) Vortex Flow Meter
3) Which type of pump has the lowest shape factor?
a) radial
b) mixed
c) axial
4) Which of the following pumps produce a pulsating flow?
a) piston pump
b) diaphragm pump
c) radial flow pump
d) gear pump
e) axial flow pump
5) Check the assumptions required for the Bernoulli Equation and for the Energy Equation.
B
E
a) Pressure is hydrostatic at both cross sections _____ x
b) frictionless
x ___ _____
c) steady flow
x ___ x
d) constant density
x ___ x
Short Answer or Quick Calculation (4 point each, total of 20 points)
1) Explain how an orifice can be used to measure flow rate.
The flow rate is proportional to the square root of the pressure drop across the orifice.
2) Why can an ADV or LDV not be used in a homogeneous, pure fluid?
Particles are needed to reflect sound or light.
3) It has been proposed that instead of returning the lake source cooling lake water directly to
the lake through a multiport diffuser that the water be pumped up to Beebe lake for use by
the hydroelectric plant located just below Beebe lake. The hydroelectric plant would be
upgraded and with the increased flow, the plant would generate additional electricity for
Cornell. Assuming that the capital costs are not prohibitive, would you recommend that
Cornell consider this option? Explain why or why not. Do not consider potential
environmental impacts when answering this question!
More energy is required to pump water up than will be gained by the turbines. This is a
perpetual motion scheme that violates conservation of energy!
4) How would an increased depth of submergence affect the piezometric head required for a
multiport diffuser if wastewater were being discharged into the ocean?
As submergence increases the piezometric head required will increase.
5) What is required for it to make sense that minor losses can be expressed as a constant times
the velocity head?
High Reynolds number
Problem solving (45 points) Note that there are constants and equations on the last
sheet of the exam
1
0.9
0.8
0.7
Efficiency
Head (m)
1) The lake source cooling intake pipe will have 3.1 km of plastic pipe (HDPE) lying on the
bottom of the lake. The plastic pipe and steel pipe will be 1.6 m in diameter and will have a
friction factor of approximately 0.018. The entrance loss coefficient is 1. You may ignore
other minor losses. The proposed plastic pipe can withstand a maximum negative pressure
differential of 25 kPa (produced by the pumps taking water out of the wet pit) between the
inside and outside of the pipe. The pump curve for a possible pump is given below. This
pump operates at a constant 210 rpm.
A) (5 points) What is the maximum flow rate that could be achieved based on plastic pipe
material constraints? (Q=2.37 m3/s)
B) (4 points) Using the pump curve given, determine the shape factor of the pump.
(S=0.413)
C) (3 points) How much shaft power is required at best efficiency point? (1.95 MW)
D) (3 points) If the maximum flow required to chill Cornell is 2.2 m3/s is this pump a good
choice? Why or why not? (Bad
choice because the operating
70
point is far to the left of the
BEP.)
60
E) (10 points) The pump is a
vertical turbine pump, and
50
pumps water out of a large wet
40
pit, or open pool. If the pump
H (m)
intake is 1 m from the wet pit
30
NPSHr (m)
floor, how deep (relative to the
lake surface) does the pit have to
Efficiency
3
20
be for a flow of 2.2 m /s. NPSHr
includes intake losses for vertical
10
turbine pumps. (reservoir depth
is 5.32 m: head loss is 2.32 m
0
and from NPSHr the pump must
0
1
2
3
4
5
6
be submerged by 2 m.)
0.6
0.5
0.4
0.3
0.2
0.1
0
Flow (m3/s)
Motor
Lake Water Surface
Steel Pipe
ipe
cP
i
t
s
Pla
0m
310
Part E?
100 m
1m
Pump inlet
length of intake pipeline is 3200 m
2) (20 points) A multiport diffuser is used to discharge 30 m3/s from the Boston wastewater
treatment plant. The diffuser is 5 m in diameter and has 100 ports spaced at 10 m intervals.
The riser loss coefficient is 4 and the friction factor is 0.02. If 1% of the flow comes out of
the first port (closest to the wastewater treatment plant) with a velocity of 3 m/s what is the
piezometric head at the second port? You may assume the two ports have the same
elevation. Use at least 4 significant digits in your calculations,
Qport = 0.3 m3/s
piezometric head at the first port is 1.8349 m
change in head due to expansion is 0.002357 m
change in head due to major losses is –0.004667 m
Head at the 2nd port is 1.8326 m
Equation/Table Sheet
Physical constants (for water at 20°C)
density = 1000 Kg/m3
specific weight = 9789 N/m3
viscosity = 1 x 10-3 N·s/m2
kinematic viscosity = 1 x 10-6 m2/s
vapor pressure = 2340 Pa
atmospheric pressure = 100 kPa
General Equations
Re 
p1

VD
hf  f
H expansion 
Vi 1Q p
i
D
Qp 
i
2 gH d
4
i
Kr
H pipe
2
L Vi1
 f
D d 2g
Hd
 H d  H expansion  H pipe
i 1
i
i
Qp
i
Ad
V12
p
V2
 z1  h p  2   2 2  z 2  ht  hL
2g

2g
L V2
8 LQ 2
hf  f 2
D 2g , or
 g D5
i
gAd
2
p
Vi 1  Vi 

 1
Multiport Diffuser Equations
Pumps
S
 Q
gH 
3 4
p
f
64
Re
CH 
laminar flow
0.25
f 
  
5.74 


log

0
.
9
Re 
  3.7 D
(Swamee Jain)
2
10.675L Q 1.852
h f  4.8704
SI units
C 
D
(Hazen-Williams)
hL
2
V1  V2 


2g
(expansion)
hL  K
V 2 (minor losses)
2g
CQ 
Hg
 2D2
Q
D 3
Po  QH P
NPSH a 
p a  pv

 hl  ( z pump  z reservoir )
i