Design, fabrication and performance investigation of a centrifugal reaction water turbine for low head and low flow application

Abstract

There are few small to medium scale low head and low flow hydro turbines commercially available, but they are very expensive and inefficient for micro power generation. Therefore, there is an intrinsic need of micro-hydro turbines that can encourage the exploitation of hydropower available in Africa’s’ small rivers and streams. The main aim of this research was to design, fabricate and test a simple, low head and low flow micro-hydro turbine model, that operate with relatively high efficiency while maintaining low cost of manufacturing. Continuum mechanics approach was adopted where the design of the single arm reaction turbine was derived from a mathematical model that was based on the balance equations formulated in a rotating control volume. Once the fabrication was complete, experimental tests were conducted on the model turbine. The tests assessed the power output and efficiency by varying the head, orifice diameter as well as the arm radius. Output power was determined from the operating torque and angular speed of the turbine. A rope brake dynamometer was attached to the turbine to find the torque and a digital tachometer was used to measure the operating angular speed. Power output of each experiment was examined in relation to the specific variables using quantitative analysis. Using the collected data, the coefficient of performance was determined. Experimental results showed that; angular speed increases with increase in the water mass flow rate. Flow-rate also increased with the increase in the radial arm length. The radial arm length affects the operating angular velocity, output torque as well as the overall turbine efficiency. The optimum nozzle to main conduit cross-sectional area ratio that gives the optimum efficiency is in the range of 0.18 to 0.24. The research achieved to build a non-complex turbine with an optimum efficiency of 83% and 40% at a head of 1.85 m and 11.5 m respectively. Theoretical efficiency was found to be 93.4%. The research concluded that the semicircular centrifugal reaction water turbine is a fairly suitable type of turbine for low head and low to medium flow application. The research recommended that an arm conduit with a larger and varying cross-sectional area could be used so as to allow higher discharge and scaling up of the turbine. However further research is still needed on how water from the reservoir gets into the turbine and exits.