radial pump impeller design (example) 1. design a rotor(impeller) of a radial water pump for the...
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1
Radial Pump Impeller Design (Example)
2
• Design a rotor(impeller) of a radial water pump for the following given values
Q = 300 m3/h (0.0833 m3/s)
H = 50 m
n = 1450 rpm
3
• The Specific speed for the pump is calculated from the following formula for the given values
• After finding the specific speed the shape of the impeller can be decided using the following table.
The specific speed is in the radial type pump range
3.2250
0833.014504343
H
Qnns
Shape No. Range Shape of the Impeller
10<ns<50 Radial Type
50<ns<150 Mixed Type
150<Ns<400 Axial Type
4
• The shaft Power is given as:
• The overall efficiency, ηo, for a single stage, single entry, radial pump can be read from the figure below to be ηo = 0.85.
• The pump power becomes,
o
QgHP
kWkWP 551.5185.0
5081.90833.0103
5
(Source: Centrifugal Pumps, Johann Friedrich Gülich, 2nd ed)
6
• Shaft diameter can be found using the following formula
• The torque can be calculated as it follows:
• The allowable shear stress for most of the shafts is in the range between 40 -60 N/mm2. Thus the shaft diameter becomes:
• The hub diameter, dh = 1.1 to 1.3 ds
316
ts
Td
Nmn
PPT 362
6014502
55000
2
mmdsaymmd ss 40,64.3513.32
mmdd sh 502.1
7
• The eye diameter (D1) can be calculated by assuming inlet number . The radial velocity at the inlet is given by:
• The volume flow rate at the suction end is given by:
• Calculating for the eye diameter,
• The volumetric efficiency is given by:
YCom 2
V
hom
QQWheredDCQ
',4
' 221
965.0,,0362.1,3.22
287.01,
287.01
13232
VsV
orn
21
4h
Vom
dC
QD
8
• The inlet number can be found from the following table.
Guidelines to choose ε
9
• From the table,
• Thus,
• Another option to estimate the value of inlet number is to use the formula by Pfleiderer,
• Thus, D1 becomes,
3.22,13.008.0 snfor
smsmCom /4/52.75.2
3
2210).35.1( sn
mmD 175.0173.005.0965.04
0833.04 21
10
The outer diameter D2 can be calculated using:
1) The head coefficient (ψ)
The head coefficient for different type of pumps is given below.
222U
gH
ψ Pump Type
0.7-1.3 Radial Impeller0.25-0.7 Mixed-flow impeller0.1-0.4 Axial Impeller
gHnD
U2
602
2
gH
nD
2602
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• Choosing ψ = 1,
2) The specific diameter (δ)
The specific diameter becomes,
mD
andsmU
412.0
,/32.31
2
2
21
41
nD
Q
DnDQ
AU
Q
U
C
Dn
Y
U
gH
m322
22222
4
4
22
2/1
4/12
2/1
32
4/1
22221
41 05.142Q
YDnD
QDnY
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• D2 becomes,
• The specific diameter is plotted in the following diagram for various specific speeds,
• From the table, δ = 6.5.
• Thus the outer diameter can be taken to be
D2 = 0.4m
4/122/05.1 QgH
D
mD 397.00833.0/5081.905.1
5.64/122
13Cordier Diagram
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• Blade width b1
• The Blade width at the outlet b2
• C2m can be found from figure below.
mmm
CD
Q
CD
Qb
omVom
40039.04175.0965.0
0833.0
'
111
mVm CD
Q
CD
Qb
22222
'
smC
figurethefromkgHkC
m
mmm
/45.3
,11.0,2
2
222
mmmb 200199.045.34.0965.0
0833.02
15
16
• Blade angle β0
• Blade angle β2 can be estimated from the previous figure.
• Number of blades
o
omom
nD
C
U
C
75.1660/1450175.0
4tan
tantan
1
1
1
1
10
oo to 3.238.21
43.04.0tan
2
2
approachStepanoffZ ,73
2
6
7,2
sin 21
12
21
Z
kofvaluethetakingDD
DDkZ