Poncelet wheel
Encyclopedia
The Poncelet wheel is a type of waterwheel invented by Jean-Victor Poncelet
while working at the École d'Application in Metz
. It roughly doubled the efficiency of existing undershot waterwheels through a series of detail improvements. The first Poncelet wheel was constructed in 1838, and the design quickly became common in France. Although the design was a great improvement on existing designs, further improvements in turbine
design rendered the Poncelet wheel obsolete by the mid-century.
was transferred to the wheel. However, much of it was also reflected off the blade and lost as heat. This process was not efficient; much of the original velocity in the water remained in it, meaning that potential energy
was not being captured. Typical undershot wheels were around 30% efficient.
Jean Charles de Borda was the first to directly characterize the efficiency of waterwheels by comparing the velocities of water before and after meeting the wheel. Poncelet was familiar with this work and started looking for ways to improve the design. He stated that "After having reflected on this, it seemed to me that we could fulfil this double condition by replacing the straight blades on ordinary wheels with curved or cylindrical blades, presenting their concavity to the current."
His design used curved blades positioned so the water met the blade flat to its edge instead of the side. This eliminated the "bounce" that robbed power from the typical design. The water rose up into the channel between the blades for about 15 degrees of rotation, and then drained back out after another 15 degrees, where it dropped out of the channel, over the curve of the blade, imparting further impulse. By the time it left, the water had almost no velocity left. He estimated that practical wheels would reach as high as 80% for low velocity streams, and 70% for high velocity ones that fill the buckets too quickly.
Poncelet developed the design in 1823 and built a small model in 1824 that demonstrated 72% efficiency. Several commercial models followed, including a large installation in Metz that delivered 33% more power than the traditional wheel it replaced, in spite of implementing only some of the design. He published a longer paper on the design in 1826, and a much more detailed version in 1827. The design won a Prix de Mecanique from the French Academy of Sciences
, who were funding development of the waterwheel and also awarded several other designs similar awards.
Poncelet wheels became common in France and Germany, where undershot designs were common. However, the large-scale installation of steam engine
s and water turbine
s led to the Poncelet wheel falling from use.
Jean-Victor Poncelet
Jean-Victor Poncelet was a French engineer and mathematician who served most notably as the commandant general of the École Polytechnique...
while working at the École d'Application in Metz
Metz
Metz is a city in the northeast of France located at the confluence of the Moselle and the Seille rivers.Metz is the capital of the Lorraine region and prefecture of the Moselle department. Located near the tripoint along the junction of France, Germany, and Luxembourg, Metz forms a central place...
. It roughly doubled the efficiency of existing undershot waterwheels through a series of detail improvements. The first Poncelet wheel was constructed in 1838, and the design quickly became common in France. Although the design was a great improvement on existing designs, further improvements in turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
design rendered the Poncelet wheel obsolete by the mid-century.
Design
Traditional undershot waterwheels consist of a series of flat blades fixed to the rim of a wheel. The blades were typically mounted so they faced straight out along the radius of the wheel. When water from the millstock flowed past the wheel, it hit the blades, and some of its momentumMomentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
was transferred to the wheel. However, much of it was also reflected off the blade and lost as heat. This process was not efficient; much of the original velocity in the water remained in it, meaning that potential energy
Potential energy
In 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...
was not being captured. Typical undershot wheels were around 30% efficient.
Jean Charles de Borda was the first to directly characterize the efficiency of waterwheels by comparing the velocities of water before and after meeting the wheel. Poncelet was familiar with this work and started looking for ways to improve the design. He stated that "After having reflected on this, it seemed to me that we could fulfil this double condition by replacing the straight blades on ordinary wheels with curved or cylindrical blades, presenting their concavity to the current."
His design used curved blades positioned so the water met the blade flat to its edge instead of the side. This eliminated the "bounce" that robbed power from the typical design. The water rose up into the channel between the blades for about 15 degrees of rotation, and then drained back out after another 15 degrees, where it dropped out of the channel, over the curve of the blade, imparting further impulse. By the time it left, the water had almost no velocity left. He estimated that practical wheels would reach as high as 80% for low velocity streams, and 70% for high velocity ones that fill the buckets too quickly.
Poncelet developed the design in 1823 and built a small model in 1824 that demonstrated 72% efficiency. Several commercial models followed, including a large installation in Metz that delivered 33% more power than the traditional wheel it replaced, in spite of implementing only some of the design. He published a longer paper on the design in 1826, and a much more detailed version in 1827. The design won a Prix de Mecanique from the French Academy of Sciences
French Academy of Sciences
The French Academy of Sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research...
, who were funding development of the waterwheel and also awarded several other designs similar awards.
Poncelet wheels became common in France and Germany, where undershot designs were common. However, the large-scale installation of steam engine
Steam engine
A 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 and water turbine
Water turbine
A 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 led to the Poncelet wheel falling from use.