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

The nd Joint International Conference on Sustainable Energy and Environment (SEE 6) B-8 (O) 1-3 November 6, Bangkok, Thailand Experimental Work 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 1.4 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 7. MW [3]. It spreads on 1.31 locations. These are in Irian Jaya about.371 MW, in Kalimantan about 1.611 MW, in Sumatera about 1.84 MW, in Sulawesi about.3 MW, in Java about 4.31 MW, in Bali + NTB + NTT about 674 MW, and in Maluku about 4 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 []. 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 to 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 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-. Therefore centrifugal volute-pumps as turbines become very attractive. Furthermore, the pump as turbine generates high shaft-revolution that is about 1. 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 nd Joint International Conference on Sustainable Energy and Environment (SEE 6) B-8 (O) 1-3 November 6, Bangkok, Thailand Performance of Volute Pump as Turbine vs Capacity 4 6 3 1.4..6.7.8.9 4 Output Power (Watt) 3 1 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 4.4. 7.6 7.87.93 1.6 Available Water Head (m) Fig. 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. 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,13 m3/menit maximum capacity, 13 m maximum head, and.4 kw power of motor..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.. Procedure of the experiment 1. Prepare the devices as in Fig. 4.. 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, p; scale reading on torque-meter m1, m; and revolution of turbine shaft, n.. Repeat the steps 3 and 4 on variation load of torque-meter up to full load (revolution is zero).

The nd Joint International Conference on Sustainable Energy and Environment (SEE 6) B-8 (O) 1-3 November 6, Bangkok, Thailand 6. Repeat the steps up to 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. 1 6 3 7 8 H = 13 m 1. Water supply tank. Overflow 3. Valve for regulating water flow capacity 4. Pump as turbine. Torque-meter 6. Rpm-meter 7. Pressure gauge, P1 8. Pressure gauge, P 9. Draft tube. V-notch weir 11. Return water supply pump 4 9 11 Fig. 4 Schematic of experiment of volute-type pump as turbine.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 p p v ( 1) ( ) H = ( z z ) + + 1 () 1 γ g Where: z 1, z = lower and upper water elevation to the turbine axis (m); p 1, p = input and output water static pressure (N/m ); and v 1, v = 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 9º v-notch weir []:, Q = 1,38. h (3) Where: Q = water flow capacity (m3/det); and h = water level at v-notch weir (m).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, 3]: T = ( F1 F ). R p = ( m1 m ). g. R p (4) where: F 1, F = the force on the belt of the prony brake (N); m 1, m = the scale reading on the prony brake (kg); g = acceleration of the gravity (m/det); 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 () in which ω = πn/6 is the angular speed in rad/sec. Turbine efficiency is simply defined as Pt η t = (6) P w 3

The nd Joint International Conference on Sustainable Energy and Environment (SEE 6) B-8 (O) 1-3 November 6, 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.. 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. m3/det which is close to the rated pump capacity at maximum efficiency i.e.. m3/det or.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.% at lower water flow capacity, i.e. at.149 m3/sec. Moreover, from Table 1 can be seen that the revolution of the pump as turbine high enough, that is about 1 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) (%) (%). 13..137.137 1,17 1,1 16.8 16. 1.88 1.33.143 13..18.3 1,4 1,36 33. 33.1 18.1 18.38.149 13..343.4 1,8 1,6 6.78 71.8 9.9 37..179 13..41.41 1,69 1,6 7.88 76. 34.34 33.4.199 13..441.443 1,7 1,7 7.4 79.36 8.63 31.3 Output-Power (Watt) 9 8 7 6 4 9 8 7 6 4..14.1.18. Flow Capacity (m3/sec) Output-Power before modification Efficiency before modification Efficiency after modification Output-Power after modification 1 Efficiency of Volute Pump, Model: CV-1...4.6.8..1.13 Flow Capacity (m 3 /min) 13. 11.8.9 9.7 8..8 1.9 Head of Pump (m) Fig. Performance of the pump as turbine before and after modification Fig. 6 Efficiency of the volute pump model CV-1 3. 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 nd Joint International Conference on Sustainable Energy and Environment (SEE 6) B-8 (O) 1-3 November 6, 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. rpm at their maximum efficiency; therefore it can be coupled directly to the load, a generator for example, without reduction gear.. 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.. 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: 7-4-4], URL: http://www.elements.nb.ca/theme/energy/micro/micro.htm. [] Evans, R.A. (3) Waterpower, [Online, accessed: 1-4-3], URL:http://www.evans.eu.com. [3] Departemen Energi dan Sumber Daya Mineral Republik Indonesia (4) Kebijakan Energi Nasional 3 : Kebijakan Energi yang Terpadu untuk Mendukung Pembangunan Nasional Berkelanjutan, Departemen Energi dan Sumber Daya Mineral, Jakarta [4] Greacen, C. (6) Project Report Huai Kra Thing Micro-hydro Project, 19 February 6, [Online, accessed: 1-4-3], URL: http://www.microhydro.com. [] Keane and Phillips (3) Characteristics of a Francis Reaction Turbine, [Online, accessed: 6-6-3], URL: http://www.microhydro.com. [6] Klunne, W. () Micro Hydropower Basics, [Online, accessed: 1-4-3], 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 (4) Micro-Hydropower Systems: A Buyer s Guide, Her Majesty the Queen in Right of Canada. [9] Steindorf, S., dan Regan, T. (1) New Turbine Can Extract Energy From Flowing Water, The Christian Science Monitor, [Online, accessed: -1-4], URL:http://www.law.cornell.edu/ uscode/17/7.shtml. [] Streeter, V.L., and Wylie, E.B. (197) Fluid Mechanics, 6th edition, McGraw-Hill Book Company, New York, ch. 8-9 [11] Suarda, M. (4) Assessment Of Performance Of A Diffuser-Pump And A Volute-Pump As Turbines, Proceeding of Research Grant Seminar of TPSDP Project, Surabaya.