Michell-Baniki turbine
Practical Action
determined quantity of blades, and which guides the water so that it enters the rotor at a
predetermined angle that ensures the greatest possible production of energy.
The energy from the water is transferred to the rotor in two stages, hence the name of the
machine as the ‘turbine of double effect’. The first stage on average transfers 70% of the total
energy to the rotor whilst the second transfers the remaining 30%.
(Research conducted by different researchers places the hydraulic performance as being between
65 and 70%, whilst others state 61%, stressing that the second stage transfers only 17%.
Mainly, literature indicate 70% up to 84%)
An attractive feature of this machine is its flat performance curve. This is achieved by designing
the turbine for partial admission. For example: if the rotor is divided into three equal parts, the
admission of water can be controlled by allowing it to enter 1/3, 2/3 or the entire wheel.
Twin control vanes
to allow from
partitioning
Rotor
Air inlet valve
Hydraulic operation of
control vanes
Bearing mount
Draught tube (always
full)
Figure 2: Partial admission cross-flow turbine
This type of admission is what enables the performance curve shown in Figure 2, where a
comparison with the performance curve of the Francis model of turbine can be observed.
As has been previously mentioned, the cross-flow turbine is particularly appropriate for rivers with
small flows.
For several months a year, these rivers carry very little water. Therefore, the turbine design is able
to take into account the minimum flow of water by partial loading and in times of abundant water,
the whole of the turbine will be used to deliver productive energy.
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