Turbine Dimensionless Coefficients and the Net Head/Flow Rate Characteristic for a Simplified Pico Hydro Power System

Abstract

The basic operational parameters of a simplified pico-hydropower system with provision for water recycling were investigated. Five simplified turbine of runner diameters 0.45, 0.40, 0.35, 0.30 and 0.25 m were designed, locally fabricated, and tested in conjunction with five PVC pipes of diameters 0.0762, 0.0635, 0.0508, 0.0445 and 0.0381 m as penstocks. Five simple nozzles of area ratios 1.0, 0.8, 0.6, 0.4 and 0.2 were fabricated for each penstock diameter. The turbines were successively mounted at the foot of an overhead reservoir such that the effective vertical height from the outlet of the reservoir to the plane of the turbine shaft was 6.95 m. A 1.11 kW electric pump was used to recycle the water downstream of the turbine back to the overhead reservoir. The mean maximum and minimum rotational speeds of the shaft of each turbine were measured for each penstock diameter and nozzle area ratio, and the volumes of water displaced in the reservoirs were also monitored. These measured data were used to compute shaft power and system volumetric flow rate for each operation. Dimensionless flow, head and power coefficients, and specific speed were computed and functional characteristics relating them developed. This standard procedure generally used for the analysis of geometrically similar hydraulic machines have been applied to this system and the results obtained will be invaluable in development of the system into a simple, environmentally friendly and decentralized small power generation system that could potentially contribute positively to the energy mix in Nigeria. The possibility of scaling the system to accommodate larger turbine and penstock diameters, and as a result higher capacity alternators exist and is a target for future developments.