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Steam-engines

the Science and technics
 
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Steam draught still provides a considerable part of energy demanded to us. Even best of modern nuclear reactors only the sources of heat transforming water in steam for rotation of turbines, connected to electrogenerators.

The First steam-engine has been invented in I century d.C. by the Greek engineer Gero Alexandria. But the first steam-engine, found practical application, has been created in 1698 by English engineer Thomas Severi. Steam was cooled in the chamber before condensate formation. As a result of sharp reduction of volume arose partsialnyj the vacuum used for pumping out of water from collieries.


Force of the piston

In the engine invented by English engineer Thomas Njukomepom apprx. 1710, steam in the cylinder pushed upwards the piston. Then the cylinder cooled, that skondensirovat steam and to return the piston in the bottom position. At condensation of steam pressure in the cylinder fell, and atmospheric pressure was enough that the piston has fallen downwards. Therefore Nju-komen named the engine paroatmosfernym. Though efficiency of this engine was above, than at car Severi, it worked very slowly and with low EFFICIENCY. This results from the fact that after cooling the cylinder needed to be heated up again to force steam to push the piston upwards, differently it was condensed at once.


Dvigatel Uatta

This problem was solved by the Scottish engineer James Uatt. In created by it in 1769 the engine of pairs went to the separate chamber for condensation. As the cylinder did not need to be heated up and cooled serially, thermal losses of the engine were rather small. Besides, engine Uatta was more high-speed as it was possible to submit bolshee quantity of steam to the cylinder as soon as the piston came back in the starting position. Thanks to it and other improvements which have been thought up by Uattom, for a steam-engine numerous practical applications were found. To approach of the Victorian epoch powerful steam locomotives have made revolution in means of transportation overland. Steam-engines also provided energy for printing of newspapers, weaving and for work of washing machines in "ярЁют№§" laundries. Steam engines were used on platforms of attractions, and farmers by means of steam draught ploughed the earth. Cleaners used working together vacuum cleaners, and in prestigious city hairdressing salons there were even brushes for massage of a head skin with a steam drive.


the Rotary motion

Rotary motion In the majority of the first steam-engines pistons moving in cylinders created back and forth motion which then could be transformed to a rotary motion by means of mechanical devices.

Steam turbines will transform at once energy of steam to a rotary motion. In XIX century some inventors experimented steam turbines, but only in 1884 English engineer Charles Parsons has created a profitable and efficient design. After some years after the invention, its turbines began to be used on courts and in current generators.


energy Transformation

Steam engines and turbines will transform heat to energy. Thus warmly from fuel burning goes on kipjachenie the waters which volume in a vaporous condition increases in 1600 times, and pressure of steam creates movement. In piston engines of pairs extends in the cylinder and pushes the piston. In steam turbines extending steam rotates the rotors equipped with shovels. In both cases of pairs gives thermal energy.

Steam engines and turbines concern engines of external combustion as heating occurs out of the working chamber, usually at the expense of fuel burning. Steam makes in the coppers which are heated up at burning of oil or coal. On atomic power stations warmly provide nuclear reactions.


Double action

In simple steam-engines of pairs creates pressure upon one party of the cylinder, forcing it to move. But in the majority of steam engines both parties of the piston are used for reception of mechanical energy. At first steam gets on one party and moves the piston forward, and then on other party, returning it back. Therefore such engines are called as engines of double action.

The Running cycle begins with steam giving on one party of the cylinder through an entrance aperture then it is closed, and steam, extending, pushes the piston downwards on the cylinder. Then steam arrives on other party of the piston, forcing it to come back back, thus steam on the first party leaves through an exhaust aperture. Steam serially moves on one of the piston parties, and other party automatically incorporates to an exhaust aperture.

In the majority of steam engines all running cycle of each piston one D-shaped valve operates. It slides backwards-forward, providing demanded connection with entrance and exhaust steam apertures. Separate valves are available for some big steam engines on either side of the piston.


the Cranked shaft

the Cranked shaft Back and forth motion will be transformed in rotary by means of a rod and a cranked shaft. The cranked shaft is the lever connected to a heavy flywheel, and the rod connects this shaft to the piston or its rod. At piston movement forward and back the cranked shaft rotates, and the flywheel levels created rotary effort.

Steam Temperature falls at its expansion in the cylinder. The similar effect can be observed, using an aerosol cylinder: thanks to gas-vytesnitelja expansion there is a sensation of a cool from an aerosol stream. In the simple steam engine of double action of pairs, extending, cools that part of the cylinder where fresh steam will move.

At strong expansion of steam the cooling effect can cause the big thermal losses in the engine. These losses it is possible to compensate for the burning account bolshego quantities of fuel, but the engine EFFICIENCY thus decreases. Temperature changes can be reduced if to limit pressure of steam submitted to the cylinder for decrease in degree of its expansion. However thus becomes less and capacity of the engine.


Kompaundy

This problem dares if to allow steam to extend partially at first in the small cylinder of a high pressure. Then fulfilled steam arrives in bolshy the cylinder of low pressure where there is its further expansion. Steam-engines with two or several such cylinders are called as the combined engines or kompaundami.

Engines with triple expansion is kompaundy with cylinders of high, average and low pressure. Such engines were widely applied on courts, and some German ships were equipped with engines with the fourth step of expansion.


Direct-flow engines

Direct-flow engines allow to lower thermal losses at the expense of sharp reduction of fluctuations of temperature in the cylinder. Steam submitted to different parts of the cylinder, extends and issued through a ring of exhaust apertures in its center. Therefore the cylinder remains rather hot along the edges and more cool in an average part where it contacts to expanded steam. Thermal losses are shown to a minimum as any part of the cylinder is not exposed to the big changes of temperature.


Turbines

The Main working body of the turbine is the rotor equipped with a number of shovels. It is in the case with the motionless shovels directing a stream of steam. High pressure steam rotates a rotor.

Steam arrives in the turbine case through nozzles. At steam release its pressure falls, and it extends. It leads to increase in its speed which can exceed speed of a sound several times. So, at expansion of steam and falling of its pressure with 12 atm. To 0,5 atm. Speed about 1100 km/s is reached.


High speed, the big energy

Moving steam with such speed possesses the big energy, but it not all is easily transferred to blades of a rotor of the turbine. For the maximum transmission of energy of steam to the turbine of its shovel should rotate with a speed which twice is less than speed of steam. But frequently it is difficult for achieving, and energy losses can be big. One of ways of the decision of the given problem - installation of several numbers of shovels of the turbine that pressure gradually decreased on each of them. Such turbines are called kompaundirovannymi on pressure. The length of shovels gradually increases in a direction from inlet to the final channel. In some turbines of pairs, having passed one number of shovels, without the further expansion goes on the second, and sometimes and on the third row. Turbines of this kind are called kompaundirovannymi on speed.


Ship turbines

By one steamships of the turbine are used as a drive for the electrogenerator developing energy for the electric motor which rotates the rowing screw. On other courts the turbine rotates the rowing screw through a number of the reducers reducing speed of rotation to rather small size, demanded for economic work of the screw.

On the big courts instead of one long rotor of the turbine it is possible to establish side by side shorter two rotors connected to one source of steam. It allows to reduce engine total length. Such rotors are called perekrestno-kompaundirovannymi.


Power stations

Huge turbines of power stations serve as drives for current generators. At capacities to 300 MVt (300 000 kw) one line of rotors of the turbine is used for one generator. At the big capacities two perekrestno-kompaundirovannyh a rotor are connected to separate generators.

Generators of power stations develop an alternating current. Such current changes the direction many times for a second.


Frequency of a network

In the majority of the countries and Western, and the Eastern Europe electrical supply systems provide giving of the current making 50 cycles (a cycle two radical changes of a direction are called) in a second. It is the frequency of a network expressed in hertz (Hz) and 50 Hz equal in this case. (1 Hz=1 cycle in a second.)

Frequency of a developed current depends on speed of rotation of turbines and generators. For manufacture of a current by frequency of 50 Hz speed of rotation of the turbine should be 3000 ob./minutes In the North America frequency of networks of an electrical supply of 60 Hz is provided at the expense of speed of rotation of turbines of 3600 ob./minutes