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Difference between Pelton Wheel and Francis Turbine
A turbine is a device which converts the energy of some fluid into rotational mechanical energy. There are a number of turbines available based on the type of input used such as steam turbine, water turbine, gas turbines, etc.
The most commonly used water turbines are Pelton wheel, Francis turbine and Kaplan turbine. Go through this article to find out the major differences between Pelton wheel and Francis turbine.
What is Pelton Wheel?
A Pelton wheel is an impulse type water turbine in which the entire pressure of water is converted into kinetic energy in a nozzle and the velocity of the jet drives the wheel. The Pelton wheel was invented by an American inventor Lester Allan Pelton.
The Pelton wheel consists of a wheel fitted with elliptical buckets along its periphery. The force of the water jet striking the buckets on the wheel drives the turbine. The Pelton wheel is the preferred water turbine in hydroelectric power stations where the available water sources have relatively high hydraulic head at the low flow rates.
What is Francis Turbine?
A Francis turbine is a type of water turbine which converts the flow of water into rotational mechanical energy. It was invented by James Bicheno Francis, a British-American civil engineer.
In electric power generation, the Francis turbine is mainly used for low to medium water heads. It consists of an outer ring of stationary guide blades fixed to the turbine casing and an inner ring of rotating blades forming the runner. The flow of water to the turbine is controlled by the guide blades. In case of the Francis turbine, the water flows radially inwards and then its direction changes to downward while passing through the runner.
In the Francis turbine, the water passes over the rotating blades of the runner which reduces the pressure and velocity of the water. This results in a reaction force which spins the turbine.
Differences between Pelton Wheel Turbine and Francis Turbine
Both Pelton wheel turbine and Francis turbine are types of water turbine. However, there are several differences between them that are listed in the following table −
| Basis of Difference | Pelton Wheel Turbine | Francis Turbine |
|---|---|---|
| Description | A Pelton wheel turbine is an impulse type water turbine in which the entire pressure of water is converted into kinetic energy in a nozzle and the velocity of the jet drives the wheel. | Francis turbine is a water turbine which works by combining both the concepts of reaction and impulse turbine, which means the turbine rotates using both impulse and reaction forces of water flowing within it. |
| Type | Pelton wheel turbine is an impulse-type water turbine. | Francis turbine is a reaction-type water turbine. |
| Direction of flow of water | In Pelton wheel turbine, the direction of water flow is tangential to the runner of the turbine. | In Francis turbine, the direction of water flow is both radially and axially, for this reason it is also called mixed flow turbine. |
| Water head | The Pelton wheel turbine is used for high water heads, normally more than 300 meters. | Francis turbine is used for low to medium water heads, usually 100 to 600 meters. |
| Turbine speed | The specific speed of a Pelton wheel turbine ranges from 12 RPM to 70 RPM. | The specific speed of a Francis turbine varies from 60 RPM to 300 RPM. |
| Energy conversion | In Pelton wheel, the all hydraulic power of water is converted into kinetic energy using nozzle and then converted into mechanical energy by rotating the turbine. | In Francis turbine, only some amount of accessible energy is converted into kinetic energy and then into mechanical energy. |
| Overall Efficiency | The overall efficiency of a Pelton wheel turbine is about 85%. | The overall efficiency of a Francis turbine is about 90%. |
| Discharge required | In Pelton turbine, the discharge required is comparatively low. | The discharge required in Francis turbine is higher than that in Pelton wheel turbine. |
| Applications | Pelton wheel turbine is used for hydroelectric power generation where the available water source has high hydraulic head and low flow rates. Pelton wheel is also used in the labs of educational institutions for experiments. |
Francis turbine is mostly used for wide range of water heads and flow rates. Francis turbines are also used in irrigation water pumping setups. |
Conclusion
The most significant difference is that a Pelton wheel turbine is an impulse type water turbine, while a Francis turbine is a reaction type water turbine.
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