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Hydraulic Turbine

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Mechanical Features and Designs
Waterwheel hydraulic turbine
A hydraulic turbine, also known as a hydro turbine or water turbine, is a turbine that converts the energy from flowing water into mechanical energy by way of a rotating shaft connected to a generator for the purpose of producing hydroelectricity in a dam.[1]. The use of modern hydraulic turbines can be traced back to the use of waterwheels that used the weight effect of water to produce energy for work. Today, modern hydraulic turbines are considered a form of fluid dynamic machinery, featuring jets, nozzles, and vanes that operate on impulse or reaction principles.[2] The three most common types of hydraulic turbines that have been developed are the Kaplan turbine, the Francis turbine and the Pelton turbine.

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[edit] History

Waterwheels are considered to be the ancient version of a modern hydraulic turbine. Waterwheels were used as far back as the first century B.C. The Romans and Greeks used waterwheels to grind corn as early as 70 B.C.[3] Eventually harnessing the power of water by means of a waterwheel spread to the rest of the ancient world and eventually throughout Europe where the early use of them was primarily limited to grinding grain and pumping water. Throughout the Middle Ages, waterwheels developed in horsepower from three to 50.[4] There were four main types of water wheels.

[edit] The Undershot Waterwheel

The first type of waterwheel ever devised as early as the first century B.C. was called an undershot waterwheel. The undershot waterwheel consisted of a horizontal shaft connected to a vertical paddle wheel with the lower segment of the paddle wheel being completely submerged into the stream or creek bed.[5] The undershot waterwheel can be viewed as the prototype of an impulse turbine in that it was driven by the force of fluid striking directly against its paddles or vanes, and produced kinetic energy. The undershot waterwheel was located in rapidly flowing rivers but only had about a 25 percent efficiency rate. In the 19th century, the concept of an undershot was revisited with substantial improvements being made to its design.[6]

[edit] The Overshot Waterwheel

The overshot waterwheel came in to use around the 14th century. Also called a gravity wheel, the overshot water wheel used the force of gravity acting vertically on the water as it traveled from the top of the wheel to the bottom.[7] It this manner, the energy source for the overshot waterwheels is potential energy because the weight of the water acts under gravity to essentially turn the wheel. As a result, the overshot waterwheel became served as the prototype for a modern reaction turbine.[8] The overshot waterwheel was particularly well suited for use in hilly terrain, often being built right into the side of a hill as was done in grain grinding.

[edit] The Pitchback Waterwheel

The pitchback waterwheel was very similar to an overshot waterwheel except that excess water typically flowed away in the direction of the rotating wheel. In an overshot waterwheel, the water would flow away in the opposite direction of the rotating wheel.[9]

[edit] The Breastshot Waterwheel

The breastshot waterwheel was developed during the Middle Ages and was a hybrid of an overshot and undershot waterwheel.

[edit] Early Hydraulic Turbine Development

The leap from the use of waterwheels to modern hydraulic turbines was a lengthy, extended process that started during the Renaissance when engineers began to study the operational characteristics of waterwheels with greater scrutiny. They soon realized that more power could be harnessed if the waterwheel was actually enclosed in some type of a chamber or encasement and that only a small amount of falling water actually struck the wheel paddle or blade, leading to the loss of energy from the onrush of water not being captured. This discovery did not immediately translate into a new type of hydraulic machine however. A lack of hydraulic knowledge and the specialized tools needed to build such a machine hampered such progress well until the late 18th century.[10]

Both problems were somewhat resolved with what is considered one of the earliest reaction turbines and the precursor to today’s modern hydraulic water turbine invented by German mathematician and naturalist Johann Andres von Segner in 1750. Segner’s archaic reaction turbine involved capturing flowing water on a horizontal axis inside a cylindrical box that contained a shaft on a runner or rotor and then flowed out through tangential openings, while the weight of the water acted upon the wheel’s inclined vanes.[11]

In 1828, Claude Bourdin, a French engineer, coined the term “turbine” from the Latin derivative ‘turbo’ which means whirling or a vortex. The term reflected the primary difference between waterwheels and the new turbines that would soon come into development that featured a swirling motion of water by passing energy to a spinning rotor.[12] A turbine would prove to process more water, spin faster, and harness bigger heads. Another distinguishing feature of early turbines from waterwheels was they were built on a vertical axis opposite of a basic waterwheel’s horizontal axis connected to a vertical shaft configuration. The blades also resembled spoons or shovels, therefore, early turbines were sometimes called “spoon wheels.”[13]

Around the same time, a student of Claude Bourdin by the name of Benoit Fourneyron invented the first modern hydraulic turbine. His first turbine was not very powerful at only six horsepower. Another drawback was that the radial outflow of water that passed through it created a problem if the water flow was reduced or load removed.[14] Eventually, he did master the building of larger sized turbines that could withstand higher pressures and delivered greater horsepower.[15] For example, his most powerful water turbine achieved a speed of 2,300 revolutions per minute at 60 horsepower, translating into an efficiency of about 80 percent.[16] Another significant contribution Fourneyron made to his machine was the addition of a distributor to control and guide water flow.[17] With Fourneyron’s machine, the advent of modern hydraulic turbines was well underway and the development of a number of different types of hydraulic turbines followed.

[edit] The Francis Turbine

In 1849, an American by the name of James Francis built a hydraulic reaction turbine that was to be an improvement of other hydraulic turbines already operating at the time. Most of these hydraulic turbines were produced with the water entering into the runners at the machine’s center and then flowed radially outward. His design changed the shape of the runner blades so they curved and the water flow turned from a radial to an axial path.[18] The Francis turbine became widely used in rivers or waterways where with water pressures or heads equivalent to 33 to 328 feet (10 to 100 m).[19]

[edit] The Pelton Turbine

In the mid 1800s, another American by the name of Lester Allen Pelton invented a hydraulic turbine for use in water heads of 295 to 2,953 feet (90 to 900 m).[20] With the Pelton turbine the water could be channeled from a high level reservoir through a long duct or penstock to a nozzle. The energy of the flowing water was then converted into kinetic energy through a high-speed jet. The jet spray of water was concentrated directly onto curved buckets affixed around the parameter of a wheel. These curved buckets turned the flow of water at 180 degrees and extracted momentum. Since the action of the wheel was contingent on the impulse created by the jet on the wheel rather than the reaction of expanding water, the Pelton turbine is considered to be an example of an impulse turbine.[21]

[edit] The Turgo Turbine

The Turgo turbine, also called a “Half Pelton”[22] turbine was invented shortly after the Pelton Wheel in 1920 by Eric Crewdson. With a Turgo turbine, the water entered on one side and then was channeled through the runner blades at a 145-degree angle before exiting out the other end. The Turgo turbine operated most effectively in water heads similar to a Pelton turbine and also sometimes featured multiple jets.[23] Another difference between the two was that a Turgo turbine was smaller than a Pelton turbine and also proved cheaper to produce.[24]

[edit] The Kaplan Turbine

The growing demand for hydroelectric power in the 20th century spearheaded the development for a turbine that could work in small water heads of 10 to 30 feet (3 to 9 m). In 1913, an Austrian engineer named Viktor Kaplan proposed a propeller type turbine. His turbine, called the Kaplan turbine, operated very similar to a boat propeller but in reverse. He also eventually changed the blade design to swivel on an axis.[25]

[edit] Advancements in Hydraulic Turbines

The trend in the use of hydraulic turbines today has been toward higher water heads and larger sized units. For example, Kaplan turbines are now typically used in heads of about 200 feet (60 m). Francis turbines are used in water heads of up to 2,000 feet (610 m) and the Pelton turbine is used in water head installations of up to 5,800 feet (1,700 m).[26]

The Francis turbine exists today as a hydropower reaction turbine that contains a runner and has water passages and anywhere from nine to 19 curved non-adjustable blades or vanes. When the water passes through the runner, it strikes the curved blades causing them to rotate and the shaft, connected to a generator, immediately transmits this into rotational movement.[27]

Kaplan turbines have retained a design like a marine propeller but may also contain gates to control the angle of fluid flow through the blades. Recent developments have also sparked an increase in the number of application Kaplan turbines are being used for. Hydro sources once abandoned due to economic and environmental fallout are now applying Kaplan turbines. Interestingly enough, Kaplan turbines have even been used as wind turbines.[28]

[edit] Features/How it Works

Hydraulic turbines today are used primarily in hydroelectric plants to generate hydroelectricity. The process in generating hydroelectricity encompasses the use of turbines in the following way.

Water is stored in a reservoir behind a dam and the water intake into the dam is near the bottom of the dam wall. Gravity causes the water to fall through a penstock inside the dam. Located at the end of this penstock is a turbine turned by the flow of moving water. The shaft on the turbine is connected directly to generator that produces power and then transfers it directly to power lines that run to individual households. Therefore, the specific role of a hydraulic turbine in the generation of hydroelectricity is to convert the energy of flowing water into mechanical energy that can be turned into electrical power.[29]

[edit] References

  1. Hydraulic Turbine. Answers.com. 2008-09-29.
  2. Hydraulic Turbine. Answers.com. 2008-09-29.
  3. Turbine History. Science. 2008-09-29.
  4. Turbine History. Science. 2008-09-29.
  5. Turbine. Encarta MSN> 2008-09-29.
  6. History of Water Machines. Gramatke. 2008-09-29.
  7. Overshot. Water Wheel Factory. 2008-09-29.
  8. Turbine History. Science. 2008-09-29.
  9. WaterWheels. Whitemill. 2008-09-29.
  10. Turbines History. Science. 2008-09-29.
  11. Turbine History. Science. 2008-09-29.
  12. A Brief History of Batteries and Stored Energy. Netaworld. 2008-09-29.
  13. History. Gramatke. 2008-09-29.
  14. Turbine. Encarta MSN> 2008-09-29.
  15. Turbine History. Science. 2008-09-29.
  16. Turbine. Encarta MSN. 2008-09-29.
  17. Turbine History. Science. 2008-09-29.
  18. Model Turbine. Geocities. 2008-09-29.
  19. Turbine. Encarta MSN. 2008-09-29.
  20. Turbine. Encarta MSN. 2008-09-29.
  21. Turbine. Encarta MSN. 2008-09-29.
  22. Turgo. Water Wheel Factory. 2008-09-29.
  23. Turgo. Water Wheel Factory. 2008-09-29.
  24. Lester Pelton. About.com. 2008-09-29.
  25. Turbine. Encarta MSN. 2008-09-29.
  26. Turbine. Encarta MSN. 2008-09-29.
  27. Water Turbine. David Darling. 2008-09-29.
  28. Water Turbine. David Darling. 2008-09-29.
  29. Hy how Works. Water. 2008-09-29.