Effect of the Number of Splined Blades of a Locally-Fabricated Turbine on the Performance of a Simplified Pico Hydropower System

Abstract

The basic operational parameters of a simplified Pico hydropower system were investigated using five locally fabricated turbines with 3, 5, 7, 9 and 11 splined blades in conjunction with a vertical penstock of diameter 0.0762 m and nozzle of diameters 0.0158, 0.0212, 0.0266, 0.0343 and 0.042 m. Water from an overhead reservoir 6.95 m high was discharged through the penstock to the turbines one after the other and recycled to the overhead reservoir using a 1.11 kW pump. For the on-load tests, a 3.9 kVA generator was linked to the system by a 6:1 pulley ratio belt drive. The mean rotational speeds of the shafts of each turbine and generator, volume of water displaced in the reservoirs and electrical quantities were measured for each nozzle diameter, while the shaft power, flow rate and efficiency were then computed. Dimensionless flow, head and power coefficients, and specific speed were computed and a functional characteristic relating them developed. The turbine with 11 blades developed a maximum voltage of 238 V with the largest nozzle diameter and a minimum voltage of 2.3 V with the smallest. The corresponding estimated power output computed using the manufacturer’s specification on the generator were 1765.96 W and 7.613 mW respectively. The mean maximum and minimum efficiencies based on the estimated power output were 0.8797 and 0.0007 respectively. This basically indicates that the larger nozzle diameters combined with the higher number spline blades favour good operation of the system. These show that the system has the potential of being a simple, environmentally friendly and decentralized small power generation system that could potentially contribute to the improvement of the Nigerian energy crisis.