Experimental Work on Modification of Impeller Tips of a Centrifugal Pump as a Turbine
by:Made Suarda
Nengah SuarnadwipaWayan Bandem Adnyana
Mechanical Engineering Department, Udayana UniversityDenpasar, Bali, Indonesia
Background• Energy crisis and environment impact• Policy on diversification and conservation
energy• There are a lot of water flow resources for
Micro-hydro or Pico-hydro• Problem in getting a turbine for a micro-hydro• Pumps As Turbine (PAT)• Pumps are widely available and relatively
cheaper than Reaction Turbines
Background• Cunningham and Atkinson [1998] stated
that centrifugal pumps could be used as practical substitutes for reaction turbines with good results
• Klunne [2000] 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.
Background
• An of-the shelf centrifugal pump running backwards as a turbine, and running the pump’s induction motor backwards as a generator (3 kW) was carried out at Huai Kra Thing village [Greacen, 2006].
Previous ResearchPerformance assessment of – a centrifugal ‘diffuser-pump’ (0,22
m3/minute maximum capacity, 46 m maximum head
– and a ‘volute-pump’ (0,13 m3/minute maximum capacity, 13 m maximum head
as hydro-turbines with various debit and head of water flow resource
Previous Research
Valve-2
by-pass pipePump as Turbine
Valve-1
Flow meter
Water Supply Pump
Prony Brake RPM meter
Water Reservoir
Pressure gauge
Previous ResearchThe result was the both type of the pumps present that the maximum efficiency as turbines performed:
•At H supply is equal to the maximum characteristic head of the pump
•At Q supply is equal to about 2/3*maximum capacity of the pump
•at shaft revolution about 1.500 rpm.
Previous ResearchEfficiency of Diffuser Pump as Turbine at Variation Head
15
17
19
21
23
25
24.62 42.97 46.03 47.56
Available Water Head (m)
Effi
cien
cy (%
)
Efficiency of Volute Pump as Turbine vs Head
0
5
10
1520
25
30
35
4.40 5.22 7.56 7.87 10.93 12.56
Available Water Head (m)
Effi
cien
cy (%
)
Previous ResearchPerformance of Volute Pump as Turbine vs Capacity
0
5
10
15
20
25
30
35
40
0.04 0.05 0.06 0.07 0.08 0.09
Flow Capacity (m3/min)
Effi
cien
cy (%
)
0
10
20
30
40
50
60
Outpu
t Pow
er (W
att)
Efficiency Turbine Output Power (Watt)
Problem
The optimum efficiency will generally be achieved when the shock losses at the inlet runner (pump impeller tips) is near zero [Lobanoff & Ross, 1996].Therefore, modification must be made to the impeller tips of the pump.
Objective
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.
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
• Then, testing is carried out by operating the pump as turbine at the maximum head of the pump, 13 meter, and at various capacities.
Methodology
In-flow
Pump vane
Impeller peripheral
Impeller tip Modification
Pump Impeller tip
Methodology
Qh
Weir box
Draft tube
Pump-As-Turbine
Torque-meter
Rpm-meter
PVC 1,5”
PVC 1”
Hp.max = 13 m
P1
P2
Reservoir
Pump
Over flow
Regulating-Valve
Results
0
10
20
30
40
50
60
70
80
90
0.0010 0.0014 0.0015 0.0018 0.0020
Flow Capacity (m3/sec)
Out
put-
Pow
er (W
att)
0
10
20
30
40
50
60
70
80
90
Effic
ienc
y (%
)
Output-Power before modif icat ion Eff iciency before modif icat ion
Eff iciency after modif icat ion Output-Power af ter modif icat ion
ResultsThe power and efficiency of the pump as turbine after modification is slightly higher than before modification. As Pump:ηmax ≅ 27%, at Q = 0.002 m3/sec or 0.13 m3/min at head about 8 metersAs Turbine before modification:ηmax ≅ 34%, at Q = 0.002 m3/sec & head about 13 metersAs Turbine before modification:ηmax ≅ 37%, at Q = 0.0015 m3/sec & head about 13 meters
ResultsPerformance of the volute pump as turbine after modification is offers better efficiency than the before one.The revolution is about 1500 rpm at maximum efficiency therefore it can be directly coupled to a generator. Its efficiency is relatively stable on varying flow capacity from rated capacity up to maximum flow capacity.
DiscussionEfficiency of Volute Pump, Model: CV-0512
0
5
10
15
20
25
30
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.13Flow Capacity (m3/min)
Effi
cien
cy (%
)
13.0 11.8 10.9 9.7 8.0 5.8 1.9 0Head of Pump (m)
Although this efficiency of pump as turbine is still low enough, it is caused by its pump is very small and its efficiency is very low.The bigger pumps will give higher efficiency
Example
Predicted Performance of PAT
H
Q Q
Hmax
QmaxPredicted Performance of Pump as Turbine, Which is operated at Hmax
Performance Curve of a Centrifugal Pump
η
ηmax of pump PAT
Conclusion
• Efficiency of the volute-pump operating as turbine after modification its impeller tips is slightly better than without modification.
• PAT generates shaft-revolution about 1.500 rpm at their maximum efficiency; therefore it can be directly drive a generator
• The maximum efficiency of the pump as turbine is performed at the rated flow capacity of the pump