Experimental Work on Modification of Impeller Tips of a Centrifugal ...

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
B-008 (O) 21-23 November 2006, Bangkok, Thailand
<strong>Experimental</strong> <strong>Work</strong> on Modification of Impeller Tips of a Centrifugal Pump as a Turbine
Made Suarda * , Nengah Suarnadwipa and Wayan B. Adnyana
Department of Mechanical Engineering, Udayana University, Bali, Indonesia
Abstract: Centrifugal volute-pumps are potential alternative solution to be using as hydro turbines, by flowing water in the reverse
direction through in the pumps. Previous experiment on assessment of performance of a diffuser-pump and a volute-pump as turbines
showed that both type of the pumps present that the maximum efficiency of the pumps as turbines performed at head of water flow
resource through the pumps as high as their maximum characteristic head of the pumps. However, the optimum efficiency will
generally be achieved when the shock losses at the inlet runner (impeller tips of the pump) is near zero. Therefore, modification must
be made to the impeller tips of the pump, plus a testing that is required to verify the performance of the finished the pump as turbine.
The aim of this research is to determine performance of a small centrifugal volute-pump as turbine at the maximum head of the pump
before and after modification of impeller tips of the pump at various capacities. This experiment performed by grinding the inlet ends
of the impeller tips of the pump to a bullet-nose shape to preclude excessive turbulence for efficiency consideration. Then, testing is
carried out by operating the pump as turbine at the maximum head of the pump, 13 meter, and at various capacities. The results show
that the output-power and efficiency of the modified impeller tips the centrifugal volute-pump as turbine slightly better than before
modified one
Keywords: Pumps, Hydro Turbines, Reverse Pumps, Pump as Turbine
1. INTRODUCTION
Now days, the world has been paced seriously energy crisis and environment impact. The current energy crisis – with rising fuel
prices – might be enough to boost the world’s appetite for renewable energy [9]. In Indonesia, energy demand growths about 15.4
percent per year. Therefore, the government has taken policy on diversification and conservation energy. Renewable energy
technologies produce profitable energy by converting natural phenomenon into useful energy forms. One of renewable energy
technology is hydropower. Hydropower systems convert hydraulic energy of water, potential and kinetic energy of water into
mechanical or electrical work, and then the water can be used for other purposes such as irrigation.
Potential hydropower in around Indonesia is predicted about 75.000 MW [3]. It spreads on 1.315 locations. These are in Irian Jaya
about 22.371 MW, in Kalimantan about 21.611 MW, in Sumatera about 15.804 MW, in Sulawesi about 10.203 MW, in Java about
4.531 MW, in Bali + NTB + NTT about 674 MW, and in Maluku about 430 MW. Especially on Bali, there is not a big hydropower
resource, but there are a lot of small hydropower resources that can be developed as micro-hydro or pico-hydro. By now, Electrical
power in Bali has been mainly supplied from Java using under seawater cables. Therefore, micro hydropowers are potential and
attractive solution.
The basic principle of hydropower is if the water can be piped from a certain level to a lower level, then the resulting water head
can be used to do work. If the water head is allowed to move a mechanical component then that movement involves the conversion of
the potential energy of the water into mechanical energy. Hydro turbines convert water head into mechanical shaft power, which can
be used to drive an electricity generator and other useful device. The selection of the best turbine for any particular hydro site
depends on the site characteristics, dominant one being head and flow available [2]. Selection also depends on the desired running
speed of the generator or other device loading the turbine. Other considerations such as whether the turbine is expected to produce
power under part-flow conditions also play an important role in the selection. All turbines have power speed characteristics. They
will tend to run most efficiently at a particular speed, head and flow combination.
However, main problem is getting a turbine for a micro hydro. Its design and fabrication are complicated, and a turbine is not
available widely in the market especially in Indonesia. In addition, reaction turbines are not available in small size. There are many
potential sites with 2 to 10 meters of head and low flow that not served by the market. So, it makes happen why micro hydropower
development is not attractive.
Because of the basic principle work of hydro-turbines are reversal of pumps, therefore, an alternative solution that can be
developed in overcoming problem to get hydro turbines are by using centrifugal pumps, by flowing water in the reverse direction
through in the pumps, as hydro turbines. Those are supported by availability of pumps widely in the market and have been massproduced
hence they were relatively cheap. It is estimated that the cost of a pump-as-turbine (PAT) is at least 50 percent less or even
lower than that of a comparable turbine [8]. Cunningham and Atkinson [1] stated that centrifugal pumps could be used as practical
substitutes for reaction turbines with good results. They can have high efficiency and are readily available (both new and used) at
price much lower than actual reaction turbines. Furthermore, Klunne [6] noted that centrifugal pumps could be used as turbines by
passing water them in reverse. However, their performance characteristics are not available and poorly understood. Therefore,
Klunne notify that further researches are required to enable the performance of pumps as turbines to be predicted more accurately.
Performance of a volute-pump as turbine showed that the maximum efficiency as turbine performed at head of water flow resource
through the pumps as high as their maximum characteristic head of the pump, and efficiency of the volute-pump operating as turbine
is slightly better than or at least equal to the pump efficiency [11], as depicted in Figs. 1-2. Therefore centrifugal volute-pumps as
turbines become very attractive. Furthermore, the pump as turbine generates high shaft-revolution that is about 1.500 rpm at their
maximum efficiency; therefore it can be coupled directly to the load, a generator for example, without gearbox.
An of-the shelf centrifugal pump running backwards as a turbine, and running the pump’s induction motor backwards as a
generator was carried out at Huai Kra Thing village [4]. The plant has worked fully functional as micro-hydropower plant that could
generate up to 3 kW.
Corresponding author: suarda@yahoo.com
1

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
B-008 (O) 21-23 November 2006, Bangkok, Thailand
Performance of Volute Pump as Turbine vs Capacity
40
60
35
50
30
Efficiency (%)
25
20
15
10
5
0
0.04 0.05 0.06 0.07 0.08 0.09
40
30
20
10
0
Output Power (Watt)
Efficiency (%)
35
30
25
20
15
10
5
Efficiency of Volute Pump as Turbine vs Head
Flow Capacity (m 3 /min)
Efficiency
Turbine Output Power (Watt)
Fig. 1 Performance the volute pump as turbine
at variation of capacity
0
4.40 5.22 7.56 7.87 10.93 12.56
Available Water Head (m)
Fig. 2 Efficiency of the volute pump as turbine
at variation of the available head
However, the optimum efficiency will generally be achieved when the shock losses at the inlet runner (pump
impeller tips) is near zero [7]. Therefore, modification must be made to the impeller tips of the pump, plus a testing that
is required to verify the performance of the finished the pump as turbine.
Pump Impeller tip
In-flow
Pump vane
Impeller peripheral
Impeller tip Modification
Fig. 3 Rework on pump impeller tip for operation as turbine
2. METHODOLOGY
This experiment performed by grinding the inlet ends of the impeller tips of the pump to a bullet-nose shape to preclude excessive
turbulence for efficiency consideration as in Fig. 3. Then, testing is carried out by operating the pump as turbine at the maximum
head of the pump, 13 meter, and at various capacities. Method of solving problem defined in problem formulation is by experiment.
The first step of this experiment is to set all devices used as in Fig. 4. The next step is to vary capacity and head of water resource,
and set for varying turbine load. Pumps that is used in this experiment is a centrifugal volute-type pump which have 0,13 m3/menit
maximum capacity, 13 m maximum head, and 0.4 kW power of motor.
2.1 Schematic of the experiment
The wire of motor of the pump is removed then connected to torsi-meter and other equipments. Its arrangement is as in Fig. 4. In
order to varying capacity of water supply is done by setting the degree open of valve (3). In order to varying load is done by setting
the load on torque-meter.
2.2 Procedure of the experiment
1. Prepare the devices as in Fig. 4.
2. Turn the valve and set on opened position that as water flow required.
3. Set the load of torque-meter on run-way (without load).
4. Record and tabulated the data such as flow Q; pressure p1, p2; scale reading on torque-meter m1, m2; and revolution of
turbine shaft, n.
5. Repeat the steps 3 and 4 on variation load of torque-meter up to full load (revolution is zero).
2

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
B-008 (O) 21-23 November 2006, Bangkok, Thailand
6. Repeat the steps 2 up to 5 on variation of water flow capacity.
7. Pull out the impeller of the pump, and modified the pump impeller tips.
8. Repeat the steps 1 up to 7.
The data that was recorded then manipulated as shown in Table 1.
2
1
6
5
3
7
8
H = 13 m
1. Water supply tank
2. Overflow
3. Valve for regulating water flow capacity
4. Pump as turbine
5. Torque-meter
6. Rpm-meter
7. Pressure gauge, P1
8. Pressure gauge, P2
9. Draft tube
10. V-notch weir
11. Return water supply pump
4
9
10
11
Fig. 4 Schematic of experiment of volute-type pump as turbine
2.3 Theoretical water power
Theoretical water power that is used to drive the turbine is
P w = γ . Q.
H (1)
Where: P w = Theoretical water power (Watt); Q = Water flow capacity (m3/det); H = Head (m); and γ = Specific weight of water
(N/m3)
The head of water can be calculated by formula:
v
2
p p
v
2
( 2 − 1)
( − )
H = ( z − z ) + +
2 1
(2)
2 1 γ 2g
Where: z 1 , z 2 = lower and upper water elevation to the turbine axis (m); p 1 , p 2 = input and output water static pressure (N/m 2 ); and v 1 ,
v 2 = input and output water velocity (m/s)
Velocity of water flow though in the turbine can be determined from flow capacity, which is measured using 90º v-notch weir
[10]:
2,50
Q = 1,38.
h
(3)
Where: Q = water flow capacity (m3/det); and h = water level at v-notch weir (m)
2.4 Turbine performance
The torque at shaft of pump as turbine is measured by using a manual prony-brake then can be calculated as follows [Keane &
Phillips, 2003]:
T = ( F1 − F2
). R p = ( m1
− m2
).
g.
R
p
(4)
where: F 1 , F 2 = the force on the belt of the prony brake (N); m 1 , m 2 = the scale reading on the prony brake (kg); g = acceleration of
the gravity (m/det2); and R p = the pulley radius of the prony brake (m).
Then, the power extracted from the pump as turbine is
P t
= T.ω (5)
in which ω = 2πn/60 is the angular speed in rad/sec.
Turbine efficiency is simply defined as
Pt
η
t
=
(6)
P
w
3

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
B-008 (O) 21-23 November 2006, Bangkok, Thailand
3. RESULTS AND DISCUSSION
3.1 Experiment Results
From the measurements and calculation that have been done as presented in Table 1, then they are plotted in the graphs as in Figs.
5. The graph shows that the power extracted from the turbine is increasing if the flow of water capacity is increased both on before
and after modification of pump impeller tips. This is accordance with moment of momentum concept that turbine power proportional
to mass flow rate. In addition, the power and efficiency of the pump as turbine after modification is slightly higher than before
modification. The maximum efficiency before modification is about 34.34% at water flow capacity about 0.002 m3/det which is
close to the rated pump capacity at maximum efficiency i.e. 0.002 m3/det or 0.13 m3/det at head about 8 meter, as shown in Fig. 6. In
the other hand, the maximum efficiency after modification is about 37.5% at lower water flow capacity, i.e. at 0.00149 m3/sec.
Moreover, from Table 1 can be seen that the revolution of the pump as turbine high enough, that is about 1500 rpm at maximum
efficiency therefore it can be directly coupled to a load such as a generator. Other interesting result of the pump as turbine is its
efficiency is relatively stable on varying flow capacity from rated capacity up to maximum flow capacity. Therefore, it is could be
operated at variation load.
Table 1 Performance of the pump as turbine before and after modification
Q H T (before) T (after) n (before) n (after) P t (before) P t (after) η t (before) η t (after)
(m3/det) (m) (N.m) (N.m) (rpm) (rpm) (Watt) (Watt) (%) (%)
0.00102 13.00 0.137 0.137 1,170 1,120 16.82 16.10 12.88 12.33
0.00143 13.00 0.218 0.235 1,450 1,360 33.05 33.51 18.12 18.38
0.00149 13.00 0.343 0.422 1,580 1,610 56.78 71.08 29.95 37.50
0.00179 13.00 0.412 0.451 1,690 1,620 72.88 76.52 34.34 33.54
0.00199 13.00 0.441 0.443 1,570 1,710 72.54 79.36 28.63 31.32
Output-Power (Watt)
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
0.0010 0.0014 0.0015 0.0018 0.0020
Flow Capacity (m3/sec)
Output-Power before modification
Efficiency before modification
Efficiency after modification
Output-Power after modification
Efficiency (%)
Efficiency (%)
30
25
20
15
10
5
Efficiency of Volute Pump, Model: CV-0512
0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.13
Flow Capacity (m 3 /min)
13.0 11.8 10.9 9.7 8.0 5.8 1.9 0
H ead of Pump (m)
Fig. 5 Performance of the pump as turbine before and after modification
Fig. 6 Efficiency of the volute pump model CV-0512
3.2 Discussion
Performance of the volute pump as turbine after modification is offers better efficiency than the before one. Although this is
changed just slightly in this experiment, where is the pump is very small but for the bigger pump as turbine will give higher effect.
Although this efficiency of pump as turbine is still low enough, it is caused by its pump is very small and its efficiency is lower. From
pump brochures can be seen that for the bigger pump it will offer higher efficiency as well up to about 86%, therefore pumps as
turbines are expected to present higher efficiency too. Moreover, this type of pump is widely available in the market from small to
big size.
Note that a pump is a turbine operated in reverse. This means that work is done to turn the impeller, which then imparts pressure
to the fluid. The principles of operation are identical. From the results can be summarized that in order to get the best performance of
a pump as turbine, it should be operated at its maximum pump head and at rated flow up to maximum flow capacity of the pump as is
presented in its brochure. The volute-pump as turbine for bigger size of pump is recommended to be modified their impeller tips for
better performance. However, for the smaller pumps, they were good enough directly operated as turbines because modification is
just give slightly effect on their performance but they need hard work on modification.
4

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
B-008 (O) 21-23 November 2006, Bangkok, Thailand
4. CONCLUSION
From the experiments and discussion, the following conclusions are obtained:
1. Efficiency of the volute-pump operating as turbine after modification its impeller tips is slightly better than without modification.
Furthermore, both pumps as turbines before and after modification generate high shaft-revolution that is about 1.500 rpm at their
maximum efficiency; therefore it can be coupled directly to the load, a generator for example, without reduction gear.
2. The maximum efficiencies of the pump as turbine both on before and after modification are performed between the rated flow
capacity of the pump at its maximum efficiency and the maximum flow capacity of the pump. In this flow range the efficiencies
of the pump as turbine are relatively flatted on varying flow capacity, therefore, it is could be operated at variation load.
3. For bigger size of Volute-pumps as turbines are recommended to be modified their impeller tips for better performance.
However, for the smaller pumps, they were good enough directly operated as turbines because modification is just give slightly
effect on their performance but they need hard work on modification.
5. ACKNOWLEDGMENTS
The authors would like to express our gratitude to TPSDP project for providing financial support. Thanks are also extended to
Mechanical Engineering Department – Udayana University, who provided me great assistances and supports.
6. REFERENCES
[1] Cunningham, P., and Atkinson, B. (1998) Micro Hydro Power in The Nineties, [Online, accessed: 7-4-2004], URL:
http://www.elements.nb.ca/theme/energy/micro/micro.htm.
[2] Evans, R.A. (2003) Waterpower, [Online, accessed: 12-4-2003], URL:http://www.evans.eu.com.
[3] Departemen Energi dan Sumber Daya Mineral Republik Indonesia (2004) Kebijakan Energi Nasional 2003 – 2020 : Kebijakan
Energi yang Terpadu untuk Mendukung Pembangunan Nasional Berkelanjutan, Departemen Energi dan Sumber Daya Mineral,
Jakarta
[4] Greacen, C. (2006) Project Report – Huai Kra Thing Micro-hydro Project, 19 February 2006, [Online, accessed: 12-4-2003],
URL: http://www.microhydro.com.
[5] Keane and Phillips (2003) Characteristics of a Francis Reaction Turbine, [Online, accessed: 26-6-2003], URL:
http://www.microhydro.com.
[6] Klunne, W. (2000) Micro Hydropower Basics, [Online, accessed: 12-4-2003], URL: http://www.microhydro.com.
[7] Lobanoff, V.S., Ross, R.R. (1996) Centrifugal Pumps: Design and Application, Jaico Publishing House, Bombay, ch. 14.
[8] Natural Resources Canada (2004) Micro-Hydropower Systems: A Buyer’s Guide, Her Majesty the Queen in Right of Canada.
[9] Steindorf, S., dan Regan, T. (2001) New Turbine Can Extract Energy From Flowing Water, The Christian Science Monitor,
[Online, accessed: 25-1-2004], URL:http://www.law.cornell.edu/ uscode/17/107.shtml.
[10] Streeter, V.L., and Wylie, E.B. (1975) Fluid Mechanics, 6th edition, McGraw-Hill Book Company, New York, ch. 8-9
[11] Suarda, M. (2004) Assessment Of Performance Of A Diffuser-Pump And A Volute-Pump As Turbines, Proceeding of Research
Grant Seminar of TPSDP Project, Surabaya.
5