| dc.description.abstract | Windpumps marketed presently do not run
satisfactorily, because it is difficult to match the
pump load to the rotor power. This project was set
out to develop a windmill which would continuously
match the pump load to the rotor power automatically.
A four-bladed windpump model was built and tested
in a wind tunnel, to simulate a mechanical power
transmission coupling, which can match the pump load
to the rotor power automatically, and hence achieve
optimum efficiency at all wind speeds.
Experiments were performed for blade pitches
between 200 and 700 and wind tunnel air speeds between
2.3 mls and 14.0 m/s. At each testing speed the model
was run, as the brake load was varied, until a steady
state situation was reached, when the rotor would
be running at optimum conditions.
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It was found that the coefficient of performance
was a function of the air speed, the angle of blade
pitch and the tip-speed ratio. For optimum operating
conditions the pitch angle and tip-speed ratio were
50° and 2.9 respectively
The highest efficiency for the model was
recorded at a tunnel air speed of 12.4 m/s. From
the model tests, it was found that a four-bladed
full size windmill would have the highest efficiency
at a pitch angle of 500, a tip-speed ratio of 2.9
and a wind speed of 10 m/s. The highest efficiency
would be appoximately 45%. It was found advisable
to design the windpump to run between 5 and 15 m/s.
As wind speeds vary between 5 and 15 m/s, it is
envisaged that efficiency will first rise from 20%
at 5 m/s to 45% at 10 mis, then it will reduce to
30% at 15 m/s. Averaged over a long period, the
average efficiency will be higher than is usually the
case. The amount by which efficiency will be improved
will be determined in further research work | en |
