КАЛУЖСКИЙ ФИЛИАЛ ГОСУДАРСТВЕННОГО ОБРАЗОВАТЕЛЬНОГО УЧРЕЖДЕНИЯ
ВЫСШЕГО ПРОФЕССИАНАЛЬНОГО ОБРАЗОВАНИЯ
«МОСКОВСКИЙ ГОСУДАРСТВЕННЫЙ ТЕХНИЧЕСКИЙ УНИВЕРСИТЕТ имени Н.Э. БАУМАНА»
(КФ МГТУ им. Н.Э. Баумана)
КАФЕДРА СЭ5-КФ «Иностранные языки»
для обучения чтению
студентов 5 семестра специальности ТС
Под редакцией В.В. Бойко
Настоящее методическое пособие предназначено для аудиторной работы студентов 5 семестра, обучающихся по специальности «Турбиностроение».
Цель пособия - подготовить студентов старших курсов к самостоятельному чтению неадаптированной научно-технической литературы по специальности, а также составлению рефератов и аннотаций. Тексты, включенные в пособие, представляют собою статьи из оригинальной англоязычной литературы: журналов, книг первых изобретателей паровых турбин, сайтов из Интернета и английской энциклопедии «Britannica».
Они отражают стиль и типичные структуры предложений научно-технической прозы. Тематика текстов освещает самые разнообразные вопросы в области турбиностроения, начиная с истории создания первых паровых турбин и объяснения понятий “первичный двигатель” и “ турбинный
принцип”работы до технических характеристик современных турбин и областей их применения. Понятийный уровень текстов соответствует курсу « Введение в специальность «Турбиностроение»», а их лексический и грамматический материал отвечает нормам программы по английскому языку для технических вузов.
В методических целях учебное пособие разделено на 3 части и предполагает следующие виды работ:
1. часть - тексты для изучающего чтения ( 4- 12 стр) 2.часть – тексты для письменного перевода дома и в аудитории (12-21 стр ). 3. часть – тексты для реферирования и аннотирования (21 – 20стр )
Данное учебное пособие снабжено словарем и таблицей мер.
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The principles of turbine operation were applied in ancient times. The waterwheel, the ancestor of the water turbine, was used for grinding grain by the Romans about 70 BC. Early devices of this sort were simple paddle wheels immersed in streams where the flow of water was available to turn the wheels. A precursor of the steam-driven turbine was supposedly constructed by Hero of Alexandria about the 1st century AD. This device operated on the principle of reaction: rotation was achieved by steam issuing from curved tubes in a manner similar to that of water issuing from a rotating lawn sprinkler. The windmill, from which the modern wind turbine developed, was already in use by the mid-7th century AD in Persia. Windmills with vertical sails on horizontal shafts appear to have reached Europe through contact with the Arabs several hundred years later.
Text №1. Turbine Definition
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TURBINE is a type of engine powered by a fast-moving fluid, such as water, steam, or gas or air. The main difference between the turbine and other types of engine is that its only movement is rotary, or turning. Its name comes from the Latin turbo, meaning "something that spins or twirls". The pistons of engines such as those of a locomotive or automobile have a back-and-forth movement which has to be changed to a rotary movement by connecting rods and cranks. This is not necessary in a turbine, whose rotary movement is convenient for driving dynamos, propellers, and other turning machinery.
An early type of turbine was the water wheel, which has been used for over 2,000 years.
Modern turbines are of two basic types. Impulse turbines have fast-moving jets of fluid (a liquid or gas) hitting the blades, and the force and velocity of impact turns the rotor. In reaction turbines, a large volume of high-pressure fluid forced through the blades which turn mainly as a result of the weight or pressure of the fluid.
Text №2. Steam Turbine Arrangement and Functions of its Parts
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A steam turbine consists of a cylinder-shaped casing containing a drum-shaped rotor, or turning part. Steam from the boiler is led through nozzles fixed to the casing so that jets of steam strike blades which are mounted in a ring round the rotor. The casing prevents any energy from the steam being lost.
For the best results, the speed of the blades should be roughly half the speed at which the steam comes out of the nozzles. Steam at a pressure of 14 bars (203 pounds per square inch, or about 14 atmospheres) comes out at more than 600 meters (2,000 feet) a second. This means that, with only one ring of blades, an enormous rotor-speed is needed for efficient working. To overcome this difficulty, the steam, after leaving the first ring of blades on the rotor, is led through another row of fixed blades, or stators, on the casing. These redirect the steam on to a second row of moving blades, from which it is led through a second row of fixed blades and so on. In this way the speed of the steam is decreased little by little as it passes through each row of blades, and when the steam leaves the row of blades at the far end of the rotor most of the energy has been taken from it. As the speed of the steam decreases, the pressure becomes lower, and the steam takes up more space, so the successive turbine stages must increase in diameter.
Read the text and answer the questions: What powers are common for the turbine? Who invented the special reduction gearing? Why are steam turbines in ships always geared? What is the difference between condensing and non- condensing turbines? How is the vacuum created in the turbine? What is its function?
Text №3. Turbine Capacity
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Turbines of this type multistage are economical, smooth, and quiet, and are made in very large sizes. Powers of 500 and 660 megawatts (670,000 and 885,000 horsepower) are common, and steam turbines of more than 1,000 megawatts (1,340,400 horsepower) have been built. Others of 2,000 megawatts (2,680,700 horsepower) are being designed.
Small high-speed steam turbines with a single row of blades were developed in 1887 by the Swedish engineer Carl Gustaf de Laval (1845-1913). It was de Laval who invented the special reduction gearing which allows a turbine rotating at high speed to drive a propeller or machine at a comparatively low speed.
Steam turbines used in ships are always geared because high-speed propellers are inefficient. The first turbine ship, the Turbine, was designed by Parsons and built at Wall send-on-Tyne, England. It had three turbines producing a total power of 1,492 kilowatts (2,000 horsepower).
Steam turbines may be either condensing or non-condensing. In a condensing turbine the steam goes from the turbine into a condenser and is cooled by cold water circulating in pipes. The steam becomes water and a vacuum is created because the water takes up less space than the steam does. The vacuum helps force steam through the turbine. The water is then pumped back into the boiler to be made into steam again.
In a non-condensing turbine the steam which has passed through the turbine is used to provide heat for buildings or in other industrial processes.
Text №4. Water Turbines
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The chief use of water turbines is for driving generators in hydroelectric power plants.
Both impulse turbines and reaction turbines make use of the energy of water under the influence of gravity. The distance of fall, or head, corresponds to steam pressure. A high head or a high steam pressure results in high water velocity or high steam velocity.
Impulse turbines known as Pelton wheels are used for heads above 300 meters (1,000 feet) (the highest used being about 1,650 meters or 5,400 feet) just as impulse steam turbines are used for high steam pressures. For heads of between 30 and 300 meters (100 and 1,000 feet), reaction turbines, of the Francis type with a fixed blade propeller is used. The Kaplan type, with a movable blade, is used for heads below 30 meters (100 feet).
In the Pelton wheel the water passes through nozzles which direct high-speed water jets at cup-shaped buckets fixed around the rim of the wheel. The wheel is enclosed in a steel casing. Usually Pelton wheels are mounted with the shaft horizontal but some are mounted vertically.
The Francis turbine has a runner with curved blades fixed along its length parallel to the shaft, enclosed in a spiral casing on the inside of which are mounted guide vanes which direct the water on to the runner. The guide vane angle can be adjusted to control the turbine speed by changing the direction of water flow. Most Francis turbines are mounted vertically.
Kaplan turbines have a runner shaped like a ship's propeller but working on the opposite principle, being forced around by the water instead of being turned by an engine and forcing the water backwards to drive the ship for wards. The pitch or angle of the turbine runner blades can be altered to give the best results. The largest water turbines are in Russia, where turbines of more than 500 megawatts (670.000 horsepower) output capacity have been installed. Speeds of water turbines vary from 1/200 revolutions per minute (r.p.m.) down to 75 r.p.m.
Text №5. Water Turbine Classes
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There are two major classes of water turbines, impulse and reaction. Hydraulic conditions at dams and waterfalls determine in large pan the type of turbine that will be most effective, impulse turbines are generally employed for high, heads of water
Low flow rates, whereas reaction turbines are primarily used for heads ranging down from about 450 m (1,500 feet) and moderate or high flow rates.
Impulse turbines extract energy from water by first convening the head of water into kinetic energy. This is accomplished by passing the water through a specially shaped nozzle that discharges a jet into the air. This jet is directed onto buckets that are fixed on the rim of the runner (rotor) and formed in such a way as to remove the maximum velocity from the water. The most widely used kind of impulse turbine is the Pelton turbine, or Pelton wheel, in which each bucket is divided in the centre by a double-curved wall so that the jet of water is split upon hitting the bucket and diverted to either side, transmitting a maximum amount of energy to the turbine.
The reaction turbine achieves rotation chiefly through the reactive force produced by the acceleration of water in the runner rather than in the supply nozzles, as in the case of impulse turbines. The precise way in which this acceleration occurs differs in the three major kinds of reaction turbines - the Francis, the Kaplan, and the Deriaz. In all of them, however, a fraction of the hydraulic pressure is first convened into velocity in the passage of the water through die inlet structure, which consists of a spiral casing and a gate device that leads to the runner. The energy from the water is transformed into mechanical energy in a single-stage runner (i.e., rotor with only one wheel of buckets or blades) that absorbs the full energy of the water.
Text №6. A Steam Turbine Condenser
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This type of machine transforms thermal energy stored in steam into work. It has supplanted all other prime movers in applications involving the generation of large amounts of electric power. The steam required to drive turbines of this kind is produced chiefly by nuclear reactors and boilers that burn coal or oil.
A steam turbine typically consists of a shaft (rotor) resting in bearings and enclosed in a cylindrically shaped casing. Jets of steam issuing from nozzles located on the periphery of the turbine cylinder and impinging on the blades or buckets attached to the shaft cause the shaft to turn. In effect, a steam turbine generates motive power in a manner akin to a windmill, except that it utilizes high-pressure steam rather than a current of air as its working medium.
Steam turbines may be classified as condensing or non-condensing, depending on whether or not the steam is exhausted to a condenser. In the first type, exhaust steam is condensed by circulating large amounts of cold water through the tubes of the condenser. This water absorbs the heat given up during condensation and carries it away. The process of continuous condensation maintains a low pressure in the condenser, thus increasing the expansion ratio of the steam (i.e., the ratio of the expanded volume of steam to its original volume) and the consequent efficiency and work output of the turbine. Because of the need to maintain the highest possible efficiency, all central-station power plants employ condensing turbines, which are connected directly to large electric generators.
In non-condensing turbines, steam, after expanding through the turbine, is exhausted to the atmosphere, a heating system, or some other kind of equipment. Machines of this type are most widely used in industrial plants where steam is needed at low or intermediate pressures and where by-product power can be generated economically by installing a non-condensing turbine between the steam generator and the equipment requiring steam.
Text №7. From the Water to the Steam Turbine
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The won realizations with water power let the researchers expect similar results with steam, too. Numerous engineers took part in the development of the steam turbine in the second half of the 19th. Century. To mention are the Englishman Charles Parsons, the Swede Carl Gustav Laval and the American Charles Curtis, who made crucial contributions for the development of the steam turbine.
Diagram: 2-step steam turbine after Parsons (1883). This turbine possesses two impellers and an idler in the center.
Since it is a steam jet and no more a water jet who meets the turbine now, the laws of thermodynamics are to be observed now. The modern steam turbine is an action turbine (no reaction turbine), i.e. the steam jet meets from a being certain nozzle the freely turning impeller. There's a high pressure in front of the turbine, while behind it a low pressure is maintained, so there's a pressure gradient: Steam shoots through the turbine to the rear end. It delivers kinetic energy to the impeller and cools down thereby: The pressure sinks.
Steam is produced in a steam boiler, which is heated in power stations by the burn of coal or gas or by atomic energy. Steam doesn't escape then, but after the passage through the turbine it is condensed in a condenser and then pushed back into the steam boiler again by a pump. This has the advantages that for example in nuclear power stations work and cooling water are clearly separated.