The
Francis turbine is a type of
water turbineA water turbine is a rotary engine that takes energy from moving water.Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy...
that was developed by
James B. FrancisJames Bicheno Francis was a British-American engineer, who invented the Francis turbine.-Early years:James Francis was born in South Leigh, near Witney, Oxfordshire in England, United Kingdom...
in
Lowell, MassachusettsLowell is a city in Middlesex County, Massachusetts, USA. According to the 2010 census, the city's population was 106,519. It is the fourth largest city in the state. Lowell and Cambridge are the county seats of Middlesex County...
. 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. They operate in a head range of ten meters to six hundred and fifty meters and are primarily used for electrical power production. The power output generally ranges from 10 to 750 megawatts, though mini-hydro installations may be lower. Runner diameters are between 1 and 10 meters. The speed range of the turbine is from 83 to 1000 rpm. Medium size and larger Francis turbines are most often arranged with a vertical shaft. Vertical shaft may also be used for small size turbines, but normally they have horizontal shaft.
Development
Water wheelA water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface...
s have been used historically to power mills of all types, but they are inefficient. Nineteenth-century efficiency improvements of
water turbineA water turbine is a rotary engine that takes energy from moving water.Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy...
s allowed them to compete with
steam engineA steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
s (wherever water was available).
In 1826
Benoit FourneyronBenoît Fourneyron was a French engineer, born in Saint-Étienne, Loire. Fourneyron made significant contributions to the development of water turbines....
developed a high efficiency (80%) outward-flow water turbine. Water was directed tangentially through the turbine runner, causing it to spin.
Jean-Victor PonceletJean-Victor Poncelet was a French engineer and mathematician who served most notably as the commandant general of the École Polytechnique...
designed an inward-flow turbine in about 1820 that used the same principles. S. B. Howd obtained a U.S. patent in 1838 for a similar design.
In 1848
James B. FrancisJames Bicheno Francis was a British-American engineer, who invented the Francis turbine.-Early years:James Francis was born in South Leigh, near Witney, Oxfordshire in England, United Kingdom...
, while working as head engineer of the
Locks and Canals companyThe Proprietors of Locks and Canals on the Merrimack River is a limited liability corporation founded on June 27, 1792, making it one of the oldest corporations in the United States....
in the water-powered factory city of
Lowell, MassachusettsLowell is a city in Middlesex County, Massachusetts, USA. According to the 2010 census, the city's population was 106,519. It is the fourth largest city in the state. Lowell and Cambridge are the county seats of Middlesex County...
, improved on these designs to create a turbine with 90% efficiency. He applied scientific principles and testing methods to produce a very efficient turbine design. More importantly, his mathematical and graphical calculation methods improved turbine design and engineering. His analytical methods allowed confident design of high efficiency turbines to exactly match a site's flow conditions.
Theory of operation
The Francis turbine is a
reactionThe third of Newton's laws of motion of classical mechanics states that forces always occur in pairs. Every action is accompanied by a reaction of equal magnitude but opposite direction. This principle is commonly known in the Latin language as actio et reactio. The attribution of which of the two...
turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A casement is needed to contain the water flow. The turbine is located between the high-pressure water source and the low-pressure water exit, usually at the base of a
damA dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
.
The inlet is spiral shaped. Guide vanes direct the water tangentially to the turbine wheel, known as a
runner. This radial flow acts on the runner's vanes, causing the runner to spin. The guide vanes (or wicket gate) may be adjustable to allow efficient turbine operation for a range of water flow conditions.
As the water moves through the runner, its spinning radius decreases, further acting on the runner. For an analogy, imagine swinging a ball on a string around in a circle; if the string is pulled short, the ball spins faster due to the conservation of angular momentum. This property, in addition to the water's pressure, helps Francis and other inward-flow turbines harness water energy efficiently.
At the exit, water acts on cup-shaped runner features, leaving with no swirl and very little
kineticThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
or
potential energyIn physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
. The turbine's exit tube is shaped to help decelerate the water flow and recover the pressure.
Application
Francis turbines may be designed for a wide range of heads and flows. This, along with their high efficiency, has made them the most widely used turbine in the world. Francis type units cover a head range from 20 to 700 meters, and their output power varies from just a few kilowatts up to one gigawatt. Large Francis turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%.
In addition to
electrical productionHydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
, they may also be used for
pumped storagePumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...
, where a reservoir is filled by the turbine (acting as a pump) during low power demand, and then reversed and used to generate power during peak demand.