Francis turbine

Francis turbine image

Type of water turbine Francis inlet scroll at the Grand Coulee Dam Side-view cutaway of a vertical Francis turbine. Here water enters horizontally in a spiral shaped pipe (spiral case) wrapped around the outside of the turbine's rotating runner and exits vertically down through the center of the turbine.

The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency.

The process of arriving at the modern Francis runner design took from 1848 to approximately 1920. It became known as the Francis turbine around 1920, being named after British-American engineer James B. Francis who in 1848 created a new turbine design.

Francis turbines are primarily used for electrical power production. The power output of the electric generators generally ranges from just a few kilowatts up to 1000 MW, though mini-hydro installations may be lower. The best performance is seen when the head height is between 100–300 metres (330–980:ft). Penstock (input pipes) diameters are between 1 and 10:m (3.3 and 32.8:ft). The speed ranges of different turbines units are from 70 to 1000:rpm. A wicket gate around the outside of the turbine's rotating runner controls the rate of water flow through the turbine for different power production rates. Francis turbines are usually mounted with a vertical shaft, to isolate water from the generator. This also facilitates installation and maintenance.

Contents

Development

Francis turbine parts Pawtucket Gatehouse in Lowell, Massachusetts; site of the first Francis turbine Francis Runner, Grand Coulee Dam

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