Experimental Work on Modification of Impeller Tips of a Centrifugal Pump as a Turbine

Transcription

1 Experimental Work on Modification of Impeller Tips of a Centrifugal Pump as a Turbine by: Made Suarda Nengah Suarnadwipa Wayan Bandem Adnyana Mechanical Engineering Department, Udayana University Denpasar, Bali, Indonesia

2 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

3 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.

4 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].

5 Previous Research Performance 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

6 Previous Research Pressure gauge Valve-1 Pump as Turbine Prony Brake RPM meter Flow meter by-pass pipe Valve-2 Water Reservoir Water Supply Pump

7 Previous Research The 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 rpm.

8 Previous Research Efficiency (%) Efficiency of Diffuser Pump as Turbine at Variation Head Available Water Head (m) Efficiency (%) Efficiency of Volute Pump as Turbine vs Head Available Water Head (m)

9 Previous Research 40 Performance of Volute Pump as Turbine vs Capacity Efficiency (%) Output Power (Watt) Flow Capacity (m 3 /min) 0 Efficiency Turbine Output Power (Watt)

10 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.

11 Objective The aim of this research is to determine performance of a small centrifugal volutepump as turbine at the maximum head of the pump before and after modification of impeller tips of the pump at various capacities.

12 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.

13 Methodology Pump Impeller tip In-flow Impeller tip Modification Impeller peripheral Pump vane

14 Methodology Reservoir Over flow PVC 1,5 H p.max = 13 m Regulating-Valve Torque-meter Rpm-meter P 1 P 2 PVC 1 Draft tube Pump-As-Turbine h Q Weir box Pump

15 Results Output-Power (Watt) Efficiency (%) Flow Capacity (m 3/sec) 0 Output-Power before modification Efficiency after modification Efficiency before modification Output-Power after modification

16 Results The power and efficiency of the pump as turbine after modification is slightly higher than before modification. As Pump: η max 27%, at Q = m3/sec or 0.13 m3/min at head about 8 meters As Turbine before modification: η max 34%, at Q = m3/sec & head about 13 meters As Turbine before modification: η max 37%, at Q = m3/sec & head about 13 meters

17 Results Performance 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.

18 Discussion Efficiency of Volute Pump, Model: CV Efficiency (%) Flow Capacity (m 3 /min) Head 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

19 Example

20 Predicted Performance of PAT H η Hmax η max of pump PAT Performance Curve of a Centrifugal Pump Qmax Q Predicted Performance of Pump as Turbine, Which is operated at Hmax Q

21 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 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

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