Turbines Case Essay Example for Free

Turbines Case Essay Definition and historical background Claude Burdin (1788–1873) was the very first person to use the word turbine. The word came from the Latin term turbo/turbines, which means a â€Å"whirling† or a â€Å"vortex.† Burdin used the term to describe the subject matter of an engineering competition being held during that time for a water power source. It would be an oversimplification to describe turbine as a rotating machine that is used to derive power or electricity from the water; a common water wheel may not immediately or necessarily be a turbine, but it definitely is a rotating machine. A more precise definition of a turbine is that it is a machine â€Å"in which the water moves relatively to the surfaces of the machine, as distinguished from machines in which such motion is secondary, as with a cylinder and piston† (Daugherty and Franzini 1965, 213–214). More broadly, to include other types of turbine, it is one of those devices or machines that is being used to channel or convert energy from a stream of fluid (liquid or gas) into mechanical energy which would eventually be used to generate electrical energy, or to support or augment another utility/device. This is done as the stream passes through a system of fixed and moving fanlike blades which causes the latter to rotate. This device (turbine) looks like a large (and sometimes small) wheel with small radiating blades around its rim. The four general classes of turbines are water or hydraulic, wind, steam, and gas turbines. Water or hydraulic, wind, and steam turbines are generally used for the generation of electricity; while the remaining one, gas turbines, is mostly being used in aircrafts (Britannica Concise Encyclopedia 2006). The principal components of simple turbines are the rotor, which in most if not all cases has blades projecting radially from the center to its periphery; the nozzles, where the working jet of fluid is directed and expanded; and blades, where the conversion of kinetic to mechanical energy takes place. Theoretical and operating principles Potential and kinetic energy both exist in a working fluid, which could be compressible or incompressible. Turbines collect this available energy by utilizing any or both of these physical principles: impulse turbines and reaction turbines. Impulse turbines change the direction of flow of a given high velocity fluid jet. The impulse, as a result of this, causes the turbine to spin or rotate, diminishing the kinetic energy of the fluid flow as this is absorbed by the device. In the case of flowing water, it comes available in purely mechanical form (water in nature is one of the most useful and efficient sources of kinetic energy). Scientific calculations show that 1 cubic meter of water can actually produce 9.8 kilojoules of pure mechanical energy for every meter that the volume of water descends. In the same way, a flow of the same volume of water for every second in a fall of 1 meter can provide 9.8 kilowatts, or 13 horsepower. Hydraulic turbines efficiency is estimated at approximately 1, meaning, almost all energy is available or utilized. This kinetic/mechanical energy can be converted to electrical energy with an efficiency of more than 95.0% (Calvert 2004). To get this much power from water, it should be extracted as it is lowered in elevation. The current in a stream, of course, is obvious. This flow comes from the open-channel movement or flow of water as influenced by gravitational forces. Simply put, holding a paddle-wheel in the stream of water will result to the paddle-wheel being rotated and from this outcome, power can be extracted (mechanical energy or electrical energy). This is an example of elementary impulse turbine, a machine acted upon by the impulse or force of moving or flowing water (Calvert 2004). In the case of reaction turbines, torque is developed as a result of fluids pressure or weight. The fluids pressure changes as it goes through the rotor blades of the turbine. There should be a pressure casement so as to contain and maintain the energy of the working fluid as it acts on the turbine stage(s). If there would be no pressure casement, the turbine must be immersed in the fluid flow, such as in the case of wind turbines. It is the casing that directs and contains the working fluid. In the case of water turbines, it maintains the suction which is imparted by the draft tube (Calvert 2004). A simple but very good example for this principle is the lawn sprinkler. In contrast to the impulse turbine, where the pressure change took place in the nozzle, the pressure change in reaction turbines occurs in the runner itself. This happens at the time that the force is exerted, hence, a reaction. Looking at the example of sprinkler, its duty is to spread water coming from it; the resulting energy from the turbine serves to move (rotate) the sprinkler head. Water flows from the center of the sprinkler going radially outward. Water under pressure comes from the center, and then jets of water that can possibly cover the area go out to the ends of the arms of the sprinkler at zero gauge pressure. The significant decrease in pressure takes place in the sprinklers arms. The water is projected at a certain angle to the radius, but it should be noted that the water from a working sprinkler actually moves along a defined radius. The jets of water do not impinge on a runner; but rather, they leave the runner, and this momentum is not converted into force, as opposed to an impulse turbine. The force residing on the runner reacts to the creation of the momentum, hence, the principle itself, reaction turbine (Calvert 2004). In any case, there is no restriction, as far as laws of physics are concerned, for any machine to utilize both principles. Many machines or devices use both of these principles as it is more efficient for the machine to be that way. Different kinds of turbines There are different kinds of turbines used in modern period: the water or hydraulic, steam, gas, and wind turbines. There are other types but these four are the most common and are usually the bases of any other turbines. Hydroelectric power stations utilize water, or hydraulic, turbine to drive their electric generators. Wisconsin, in 1882, witnessed the first of this kind of turbines. The processes taking place in a hydraulic turbine is simple: falling water hits a set of buckets or blades connected to a shaft. This impact will cause the shaft to rotate and move the rotors of the generator. The most common kinds of hydraulic turbine are the Francis turbine, Pelton wheel, and the Kaplan turbine. Two engineers, Sir Charles A. Parsons and Carl G. P. de Laval (of Great Britain and Sweden, respectively), pioneered the building of hydraulic turbines during the late 19th century. Continual developments and improvements of basic machines made hydraulic turbines to be the main power sources utilized to drive most large electric generators (Reynolds 1970). Another kind of turbine is the steam turbine. This is typically consist of conical steel shell that encloses a central shaft wherein a set of bladed disks are placed like washers. These blades are bent and extend outward (radially) from the edge of each disk. Some steam turbines have shafts that are surrounded by a drum wherein the rows of blades are attached. In between each pair of disks, there is a row of stationary vanes that are attached to the steel shell. These extend radially inward. Each set of vanes together with the bladed disk immediately situated/placed beside it constitutes one stage of the steam turbine. Most steam turbines have multistage engines (Columbia Electronic Encyclopedia [Online edition], 2007). Steam turbines are used mostly for electricity generation in thermal power plants, (i.e., plants using fuel oil or coal, or nuclear power). Steam turbines were once used to drive mechanical devices such as in the case of ships propellers. However, most such applications now utilize an intermediate electrical step or reduction gears. Gas turbines are now used mostly for aircraft engines. But there are still some gas turbines being used to drive electric generators (i.e., in an electric–gas turbine locomotive) as well as high-speed tools. The essential components of a gas turbine are (a) compressor, (b) combustion chamber, and (c) turbine that somehow resembles that of a steam turbine (refer to the description in the previous paragraph). The compressor is driven by the turbine, and then provides high-pressure air into the combustion chamber. In this chamber, the high-pressure air is mixed with a fuel and then burned. This makes the high-pressure gas(es) drive the turbine, with the same gas(es) expanding until their pressure decreases and reaches atmospheric pressure (Columbia Electronic Encyclopedia [Online edition], 2007). The last kind of turbine is the wind turbine, which as the name suggests converts the kinetic energy coming from the wind into mechanical and/or electrical energy. If the resulting mechanical energy is directly used by a nearby or even attached machinery (e.g., pump or grinding stones), the turbine device is usually referred to as a windmill. But if this mechanical energy is used to generate electricity, then, the device is called a wind turbine, wind generator, or wind energy converter (WEC; Reynolds 1970). Wind turbines can be three-bladed, two-bladed, or even one-bladed (counterbalanced). Computer-controlled motors point them to the direction of the winds. Danish turbine manufacturers have utilized the three-bladed turbine type. This type of wind turbine has high tip speeds (even reaching up to 6 times the speed of the wind), low torque ripple, and high efficiency, which contributes to the overall good reliability. This type of turbine is the one that is being commercially used to generate electricity. In many cases, the blades are colored in such a way that it blends with the clouds. The length of these blades usually ranges from 20 to 40 meters (or about 70 to 100 feet) or more, while the height is about 200 to 295 feet. Contemporary wind turbine models rotate at a speed of 16.6 rpm (revolution per minute). As a safety precaution to avoid overspeed damage, most wind turbines are equipped with automatic shutdown features during strong winds (Reynolds 1970; Wikipedia, The Free Encyclopedia 2007). There are other kinds of turbines, albeit fewer and smaller ones, in existence. These are the transonic turbines, contra-rotating turbines, statorless turbines, ceramic turbines, and shroudless turbine. Other uses of turbines Almost all electrical energy being used on Earth is generated with any one of the turbines discussed. Turbines with high efficiency can harness approximately 40% of the produced thermal energy, with the rest of the output exhausted as waste heat. Turbines are being utilized by most jet engines to provide mechanical energy from their fuel and working fluid as do most, if not all, power plants and nuclear ships. Reciprocating piston engines (like those found in aircraft engines) can utilize a turbine to drive an intake-air compressor. This configuration is known as the turbocharger (or turbine supercharger) or more colloquially known as â€Å"turbo.† Most turbines are capable of having very high power density the ratio of power to volume, or power to weight. This is due to their ability to function at extremely high speeds (Wikipedia, The Free Encyclopedia 2007). As of yet, no one has established any limitation for this invention of humankind. And with enough research and development, the present capability of these machines can even yield astonishing achievements. Woks Cited Calvert, J. B. â€Å"Turbines.† Date accessed: November 29, 2007 (http://mysite.du.edu/~jcalvert/tech/fluids/turbine.htm). Daugherty, R. L., and J. B. Franzini. Fluid Mechanics. 6th ed. New York: McGraw-Hill, 1965. Reynolds, J. Windmills and Watermills. New York: Praeger, 1970. Strandh, S. A History of the Machine. New York: AW Publishers, 1979. â€Å"Turbine.† Britannica Concise Encyclopedia. Encyclopedia Britannica, Inc., 2006. Date accessed: November 29, 2007 (http://www.answers.com/topic/turbine). â€Å"Turbine.† The Columbia Electronic Encyclopedia. 6th ed. Columbia University Press, 2003. Date accessed: November 29, 2007 (http://www.answers.com/topic/turbine). â€Å"Wind turbine.† Wikipedia, The Free Encyclopedia. Wikimedia Foundation, Inc. Date accessed: November 29, 2007 (http://en.wikipedia.org/w/index.php?title=Wind_turbineoldid=173495357).