Centrifugal Pump Experiment
A. Amirfazli
Feb. 2009
Impeller
Eye of impeller
(where liquid
enters the pump)
Casing (aka volute)
Fluidedesign.com
1
Pump History
„
The ancient Egyptians used water wheels with buckets
mounted on them to move water for irrigation.
„
The true centrifugal pumps were developed in the late 1600`s
by DENIS PAPIN, a French -born inventor accredited with a
pumping device having straight vanes.
„
The British inventor-JOHN G. APPOLD, was responsible for
first introducing the CURVED VANE IN 1851.
2
1
Centrifugal Pumps
„
Centrifugal Pumps belong to wider group of
fluid machines called turbo machines.
„
Pumps add energy to a fluid stream. As
such they have a wide application:
‰
Water distribution systems
„
‰
Industrial processes
„
‰
Buildings; municipality; irrigation (farming).
Oil pipelines; power plants; refineries
Machineries
„
Lubrication; fuel
3
OBJECTIVES
1.
To measure the performance of a centrifugal pump
and compare the results with theoretical predictions.
2.
To compare them with the manufacturer’s
specification.
3.
To investigate affinity laws for pumps (MecE 330).
4.
To study the performance characteristics of pumps
in parallel and series system configurations.
4
2
Centrifugal Pump
Impeller
Eye of impeller
(where liquid
enters the pump)
Casing (aka volute)
Fluidedesign.com
5
6
3
motor
outlet
inlet
pump
7
Experimental Setup
Return line
Pressure transducer
tank
Measurement tank (flow rate)
pumps
8
4
Piping arrangement for conducting series or parallel
pump experiments
9
Experimental Measurements
„
The head produced by
pumps is measured
(pressure transducer)
„
The flow rate of the
pumps is measured
(gravitometry method…
similar to Boiler Exp.)
10
5
„
Torque is measured by determining the force required to
hold the motor casing steady
„
The RPM (rotational speed) of pump is selected/set
„
The geometrical information for pump impeller (vane
angles, radius, etc.) is known/given
11
Head-Discharge Curve
10
1500 RPM
Head, H (m)
9
1100 RPM
8
7
750 RPM
Shut-off head
6
5
4
3
2
1
0
0
20
40
60 -4 3
80
Flow rate, Q (x10 m /s)
100
12
6
Velocity Triangle and Adding Energy to the Fluid
Top view
Side view
V2
U = Ω.r2
V2θ
V2r
V1
V2rel
r1
β2
b
V2
r2
V2
13
RED: high pressure
impeller eye
www.fortunecity.com
BLUE: low pressure
impeller tip
14
7
Euler Equation
„
„
.
Angular momentum (T): T = mr2V2θ
From velocity triangle we have: V2θ = U –V2rcotβ2
.
‰ therefore: T = m.r2 [U –V2rcotβ2]
.
From energy eqn.: TΩ = mgH
Then:
H=
U2
g
and
⎡ V2 r
⎤
⎢1 − U cot β 2 ⎥
⎣
⎦
U = r2 Ω
Euler Eqn.
15
Non-dimensional Euler Eqn.
Ψ = 1 − Φ cot β 2
Where Ψ Head Coefficient (= Hg/U2) and
Φ Flow Coefficient (= V2r /U)
ideal
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8
Experimental calculation for Φ and Ψ
„
„
Ψ (= Hg/U2) is easy to calculate since we
directly measure H and we know RPM and
radius of the impeller which gives us U (=Ω.r2)
To calculate Φ (= V2r /U) again as above we
have U, but need V2r (= Q / A exit )
ƒ
Q is directly measured, but Aexit needs to
be calculated!
17
Exit area (Aexit) is equal to area at the impeller outlet
minus vane thickness, i.e. Aexit = (2πr2 – 5t).b
Impeller
thickness at exit
r2
There are 5 vanes
in the impeller
Vane thickness (t)
Outer
edge
β2 β2
β2 on average
is ~28°
18
9
Head Coefficient Ψ
Dimensionless Head and Flow Coefficients
1.2
1500 RPM
1.0
1100 RPM
750 RPM
0.8
Manufacturer
(1750 RPM)
Ideal (Euler's)
0.6
0.4
0.2
0.0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Flow Coefficient Φ
Shut-off head actual (head at zero flow rate) is ~50% of
the shut-off head ideal (= U2/g), why?
19
Deviations from Theory
„
Frictional losses in the impeller and casing is not
considered in the theory
‰
These frictional losses increase with Q
„
Angle at which the fluid leaves the impeller is not
β2 (it is always less due to slip)
„
The flow in the impeller is not uniform (1dimensional) as assumed in theory.
„
Some leakage from outlet to inlet of the pump
due to clearance between impeller and casing
20
10
Affinity Laws
„
Manufacturers to offer a wide range of
pumps use geometrical similarity to
enlarge or shrink a particular design.
„
If the Reynolds numbers are large, the
head and flow coefficient for geometrically
similar pumps will remain constant and
therefore:
Q1 Ω1 ⎛ D1
⎜
=
Q2 Ω 2 ⎜⎝ D2
⎞
⎟⎟
⎠
H 1 ⎛ D1Ω1
=⎜
H 2 ⎜⎝ D2 Ω 2
3
⎞
⎟⎟
⎠
2
21
Dimensionless head versus flow coefficient curves for
geometrically similar machines
1.0
0.9
Unit 454
Unit 453
0.8
Unit 452
Unit 451
0.7
0.6
Head
coefficient
0.5
0.4
0.3
0.2
0.1
0.0
0.00
0.05
0.10
0.15
Flow coefficient
22
11
Cut Impeller
„
Manufacturer to save on development costs, but
to offer wide range of pumps with various headflow characteristics often cut impellers and place
them in the same casing.
„
Cut impeller pumps are NOT geometrically
similar; therefore affinity laws will not apply!
23
Typical Pump Curve
www.fortunecity.com
24
12
Dimensionless head versus flow coefficient
curves for geometrically dissimilar machines
(cut impeller)
0.8
Unit 454
Unit 453
Unit 452
Head coefficient
0.7
0.6
Unit 451
0.5
0.4
0.3
0.2
0.1
0.0
0.00
0.05
0.10
0.15
0.20
Flow coefficient
25
Flow Efficiency
„
Flow efficiency (η) is a measure of how much
of the input power (=TΩ) is converted to the
fluid power (=pgQH).
η=
ρgQH
TΩ
26
13
Efficiency versus flow coefficient curves
80.0
70.0
Efficiency (%)
60.0
50.0
40.0
1500 RPM
1100 RPM
30.0
750 RPM
20.0
Manufacturer
(1750 RPM)
10.0
0.0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Flow coefficient
27
Pumps in Series
Q = Q1 = Q2
H = H1+ H2
28
14
Pumps in Series
30
Head m
25
2 pumps in series
20
15
A single pump
10
5
0
0
20
40
60
-4
80
100
3
Flow rate (x10 ) m /s
29
Pumps in Parallel
H = H1 = H2
Q = Q1+ Q2
30
15
Final Note
„
Check the lab manual for details of what to
report and answer any questions posed.
31
16