Selecting the Best Type of Water Turbine Design
Selecting the best type of water turbine design for your particular situation often depends on the amount of head and flow rate that is available at your particular location and whether it is at the side of a river or stream, or the water is to be channelled or piped directly to your location.
Other factors include whether you want an enclosed “reaction turbine design” such as the Francis turbine or an open “impulse turbine design”, such as the Pelton turbine as well as the speed of rotation of your proposed electrical generator.
By analysing all of these factors together you can get some indication of what type of Water Turbine Design may work best for your particular situation. Knowing the difference between a Pelton and Francis turbine for example, will help make the choice easier.
The following table gives a basic idea of which particular Water Turbine Design we have discussed above works best according to the available head height and water pressure.
Turbine Design against Head Pressure
We can see from the table above that there is an overlap between Pelton and Cross-flow turbines, and again between Francis and Kaplan turbines. This means, that both types of turbines are suitable for such combinations of head height and flow.
An alternative to the different types of water turbines detailed above, is the use of standard water pumps as water turbines. The inverse use of water pumps as water turbines for small hydropower plants has become a popular alternative to the more expensive water turbines due to their availability and cheap cost.
Unfortunately using water pumps as water turbines has a few disadvantages such as, their efficiency is greatly reduced compared to turbines using the same head height, and that pumps used as turbines are more sensitive to cavitation and operating range.
The main difference between the operation of a pump as a turbine is that the water flowing to the pump is determined by the head height, of which there is not control, while a water turbine has flow control through the nozzles and blades, which is one of the reasons for its higher cost.
One final thought, If the water turbine is to be used with and electrical generator to convert the turbines mechanical energy into electrical energy, a gearbox or pulley system may be required as the rotational speed of the turbine may be too low compared to the rotational speed required by the generator.
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