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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