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.
