The Francis turbine is an internal flow reaction turbine that converts the energy of flowing water into electricity. It was invented by James Francis in 1849 and is the most efficient water turbine in the world. Its design uses changing water pressure and the law of conservation of angular momentum to capture the water’s energy with little waste. The turbine is versatile, with adjustable guide vanes and a wide range of hydraulic “head” and power generation capabilities. It can also be used to pump water to higher elevations for later use.
The Francis turbine is a water wheel that uses the energy of flowing water and transforms it into electricity. It is an internal flow reaction turbine, also known as a radial flow turbine. This means that the water flows from the outside of the wheel through guide vanes which direct it towards the center of the wheel, where it exits the machine. As the water flows, it spins the turbine wheel, a central cylinder with an average of nine to 19 curved blade-shaped spokes. This motion is transmitted from a shaft to a generator, where the energy of the water is converted into electricity.
The machine was invented in 1849 by the American scientist James Francis, after whom the machine is named. He has conducted numerous experiments on the design of water turbines. His discoveries allowed him to improve the existing internal flow reaction turbine, increasing its efficiency to over 90%. It is the most efficient water turbine in the world and is also the most used.
Francis’ modification of the standard turbine design made use of changing water pressure and the law of conservation of angular momentum. Water enters the turbine from a high-pressure source and flows through a spiral with gradually decreasing radius, causing its pressure and angular momentum to decrease and its speed to increase. The fast-moving water spins the runner with increasing force as it approaches its center, capturing the water’s energy with little waste. The water then exits the runner and exits through a pipe designed to slow the water down. This allows the water to be returned to the source gently, without excessive currents or eddies.
In addition to its incredible efficiency, the Francis turbine is appreciated for its versatility. Adjustable guide vanes regulate the flow of incoming water, keeping the speed of the runner constant, and therefore the power delivered, regardless of the variations in the flow rate of the spring water. Hydraulic “head” is a measure of a fluid’s energy per unit of weight, and the Francis turbine can be designed to operate in a head range of approximately 10 to 700 metres. It can also generate power over a wide range from a few kilowatts to nearly a gigawatt.
Unlike an older water wheel, the axis of a Francis turbine is vertical. Seen from above or in a horizontal section, the machine looks a bit like the shell of a snail. In addition to generating power, this type of turbine can also be used to pump water to reservoirs at higher elevations, where it can later be redirected through the turbine to produce more electricity.
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