Influence of Number of Flat Locally-Fabricated Turbine Blades on the Performance of a Simplified Pico Hydropower System

Abstract

Five locally fabricated turbines with 3, 5, 7, 9 and 11 flat blades were locally fabricated and tested in conjunction with a vertical penstock of diameter 0.0762 m and nozzles of diameters 0.0158, 0.0212, 0.0266, 0.0343 and 0.042 m in a simplified Pico hydropower system. This study is an aspect of an ongoing work aimed at ultimately implementing the system for small power generation. The turbines were mounted at the foot of an overhead reservoir 6.95 m high. A 1.11 kW pump was used to recycle the water downstream of the turbine from an underground reservoir to the overhead reservoir, and a 3.9 kVA alternator used for the on-load tests. The turbine was linked to a 3.9 kVA alternator by a belt drive of pulley ratio of 6:1. The mean rotational speeds of each turbine and alternator shafts, volume of water displaced, and voltage developed were measured for each nozzle diameter. These data were used to compute flow rate, shaft and electrical power, and efficiency for each operation. Dimensionless flow, head and power coefficients as well as specific speed were computed and functional characteristic curves relating plotted. The turbine with 11 blades developed the maximum voltage with the nozzle diameter of 0.042 m and the least voltage for 0.0158 m diameter nozzle. The corresponding estimated power output computed using the manufacturer’s specifications on the alternator was also highest and the mean maximum efficiency based on the estimated power output was 0.4482. This indicates that the larger nozzle diameters combined with the turbine with higher number of flat blades favour beneficial system operation. The results indicate good potential for the system as a simple, environmentally friendly and decentralized small power generation system that can contribute to the current energy mix in Nigeria.