2015-08-21
474The steamturbine consists of two principal elements: (1) a device for converting some of the thermal energy of the steam into kinetic energy, (2) a suitable mechanical arrangement for converting the kinetic energy of the steam into shaft work.
The nozzleaccomplishes the change in form of the steam energy, whereas blades mounted upon a rotor absorb the kinetic energy of the steam when it passes through the channels formed by the blades. Depending upon the form of the turbine the nozzle may be a separate device, as compared to the blades, or blades may also perform the functions of a nozzle. Steam turbines may be classified as (1) impulse turbine, (2) reaction turbine.
In the impulse turbine the steam passes through a stationary nozzle while dropping in pressure. The high velocity jet issuing from the nozzle smoothly impinges on a row of moving blades and passes between them at constant pressure. The change in momentum that the steam undergoes, owing to change in direction during the passage, causes a force to act on the moving blades, thereby doing mechanical work.
Fig. 1.
A - Impulse Turbine Stage, В - Reaction Turbine Stage (P - pressure Changes, С - Velocity Changes)
In the reaction turbine the stationary nozzles have the same appearance as the moving blading. The steam drops in pressure while passing through both the stationary nozzles and the moving blading. Thus the force acting on the moving blading is derived not only from changing the direction of the steam.
Fig. 2. Double Flow Turbine of a Main Turbo-generator
Turbines may be classed according to the arrangement of steam flow through the unit as a whole:
(1) single flow,
(2) double flow,
(3) single-double flow.
Single flow indicates that all steam enters at one point (the throttle) and flows essentially in a single stream to the exhaust. Double flow indicates entry at one point, but the steam is then divided into two equal streams flowing in opposite directions through the unit and may or may not exhaust at a common point from the unit. In the single-double flow units the steam flows part way as a single stream and then is divided into two streams for the remainder of its passage through the unit.
Turbines are classed also as
(1) single cylinder and
(2) compound.
Single cylinder indicates that the unit consists of one turbine contained in one casing.
A compound unit consists of two or more individual turbines, the exhaust of the high pressure turbine feeding one or more low pressure turbines.
Compound units are further classified as
(1) tandem compound,
(2) cross-compound.
In the tandem compound unit all the individual turbines are mounted upon a common shaft. In the cross compound unit each turbine has a separate shaft.
Depending upon their application, turbines are also classed as
(1) condensing,
(2) non-condensing.
The condensing turbines exhaust their steam to a condenser which maintains a back pressure. The non-condensing turbine usually exhausts its steam to another device where it is used for heating. The back pressure may vary from below atmospheric to several hundred pounds depending upon the application of the exhaust steam.
EXERCISES
I. Give synonyms to the following words: to convert, energy, frequent, to pass, force, to vary, to apply, exhaust, to unload, to generate, to accelerate, to permit, to design, speed.
II. Give opposites to the following words: most, smooth, above, unequal, high, stationary, exhaust, to unload, dirty.
III. Translate the following groups of words into Russian: present day marine turbine practice; back pressure turbine; feed water heating; high velocity jet suitable mechanical arrangement; low pressure shaft seal; high powered geared steam turbine propulsion.
IV. Translate the following sentences into Russian, paying attention to
the -ed and the -ing forms:
1. The first stage nozzles are usually arranged in groups so that the amount of steam admitted to the turbine can be controlled by increasing or diminishing the number of nozzles through which steam is admitted.
2. A simple impulse turbine consists of a ring of nozzles followed by a row of blades mounted on a wheel and facing the nozzles.
3. In a reaction stage the velocity increases in the fixed blades and is reduced on entering the moving blades.
4. By keeping the energy conversion per stage comparatively small, good efficiency can be obtained with moderate turbine speed.
5. The steam impinging upon the blades propels them forward and having traveled over the concave surface of the blades leaves it at the outer side having almost completely lost its absolute velocity.
V. Answer the following questions:
1. What types of turbines do you know?
2. What is an impulse turbine?
3. What is a reaction turbine?
4. What principal parts does a steam turbine consist of?
VI. Translate the following sentences into English:
1. Паровые турбины служат для превращения тепловой энергии пара в механическую работу.
2. В процессе истечения пара через сопла потенциальная энергия пара преобразуется в кинетическую.
3. Пар поступает в сопла, где он расширяется.
4. Во время этого расширения пар приобретает значительную скорость.
5. В активных турбинах расширение пара происходит только в соплах.
6. В реактивных турбинах пар расширяется как на неподвижных, так и на рабочих лопатках.
VII. Supply the corresponding term to the given definitions:
· a rotary motor or engine driven by a flow of water, steam, gas, wind, etc., esp. to produce electrical power = …
· remaining in one place, not moving; not meant to be moved; not portable =...
· the quantity of motion of a moving body, measured as a product of its mass and velocity = …
· the measure of the rate of movement of a usually inanimate object in a given direction = …
· the flattened functional part of an oar, spade, propeller, bat, skate, etc. = …
· a valve controlling the flow of fuel or steam etc. in an engine = …
VII. Insert the prepositions:
The steam turbine consists (1) ___ two principal elements: a device (2) ___ converting some of the thermal energy of the steam (3) ___ kinetic energy, a suitable mechanical arrangement (4)___ converting the kinetic energy of the steam (5)___ shaft work. The nozzle accomplishes the change (6)___ form of the steam energy, whereas blades mounted (7) ___ a rotor absorb the kinetic energy of the steam when it passes (8)___ the channels formed (9)___ the blades. Depending (10)___ the form of the turbine the nozzle may be a separate device, as compared (11) ___ the blades, or blades may also perform the functions of a nozzle.
In the impulse turbine the steam passes (12) ___ a stationary nozzle while dropping (13) ___ pressure. The high velocity jet issuing from the nozzle smoothly impinges (14) ___ a row of moving blades and passes between them (15) ___ constant pressure. The change (16) ___ momentum that the steam undergoes, owing (17) ___ change in direction during the passage, causes a force to act (18)___ the moving blades, thereby doing mechanical work. In the reaction turbine the stationary nozzles have the same appearance as the moving blading. The steam drops (19) ___ pressure while passing (20)___ both the stationary nozzles and the moving blading. Thus the force acting (21)___ the moving blading is derived not only (22)___ changing the direction of the steam.
Turbines may be classed according (23) ___ the arrangement of steam flow (24) ___ the unit as a whole: single flow, double flow, single-double flow. Single flow indicates that all steam enters (25) ___ one point (the throttle) and flows essentially (26) ___ a single stream to the exhaust. Double flow indicates entry (27) ___ one point, but the steam is then divided (28) ___ two equal streams flowing (29) ___ opposite directions (30)___ the unit and may or may not exhaust (31)___ a common point from the unit.
In the single-double flow units the steam flows part way as a single stream and then is divided (32)___ two streams (33)___ the remainder of its passage (34)___ the unit. Single cylinder indicates that the unit consists (35)___ one turbine contained (36)___ one casing. A compound unit consists (37)___ two or more individual turbines, the exhaust of the high pressure turbine feeding one or more low pressure turbines. In the tandem compound unit all the individual turbines are mounted (38)___ a common shaft. In the cross compound unit each turbine has a separate shaft. The condensing turbines exhaust their steam (39) ___ a condenser which maintains a back pressure. The non-condensing turbine usually exhausts its steam (40) ___ another device where it is used (41) ___ heating. The back pressure may vary (42)___ below atmospheric (43) ___ several hundred pounds depending (44)___ the application of the exhaust steam.
VIII. Fill in the table of derivatives (where possible):
| VERB | NOUN | ADJECTIVE | ADVERB |
| entry | |||
| apply | |||
| various | |||
| separate | |||
| arrange | |||
| depend | |||
| indication | |||
| container |
