que & ans other than turbine

8/3/2019 Que & Ans Other Than Turbine

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1. Where is an evaporative condenser used in practice?

Answer:

In those cases where the shortage of cooling water is acute.

2. What should be the basic criteria for an efficient steam condenser?

Answers:

1. Maximum amount of steam condensed per unit area of available heat transfer surface.2. Minimum quantity of circulating coolant required.3. Minimum heat transfer surface required per kW capacity4. Minimum power drawn by the auxiliaries.

3. Why must a vacuum be maintained in the steam condenser?

Answers:

1. By maintaining a vacuum in the steam condenser, the efficiency of the steam-power plant caincreased as greater the vacuum in the system, greater will be the enthalpy drop of steam.Therefore, more work will be available per kg of steam condensing.

2. Secondly, the non-condensate (air) can be removed from the condensate-steam circuit by puand maintaining a vacuum in the steam side. Therefore, the condensate can be used as boilefeed.

4. What are the limitations of a surface condenser?

Answers:

1. It is very bulky and as such requires more floor space.2. Its manufacturing, running and maintenance costs are high.

5. What should be the requirements of an ideal surface condenser used for steam power plants

Answers:

1. Uniform distribution of exhaust steam throughout the heat transfer surface of the condenser.2. Absence of condensate sub cooling.3. There should not be any leakage of air into the condenser.4. There should not be any tube leakage.5. The heat transfer surface in contact with cooling water must be free from any deposit as scal

reduces the efficiency of heat exchangers.6. What do you mean by vacuum?

Answer:

Vacuum means any pressure below atmospheric pressure.

7. How is vacuum in a condenser usually measured?

Answer:

It is measured by means of a Bourdon pressure gauge, which is calibrated to read the pressure in mmercury below atmospheric pressure.

8. On what factors does the degree of vacuum in a condenser depend?

Answers:


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It depends on the partial pressure of steam and the partial pressure of air in the condenser.

9. What is the vacuum efficiency of a condenser?

Answers:

It is the ratio of the actual vacuum at the steam inlet to the maximum obtainable vacuum in a perfectcondensing plant, i.e., it is the ratio of actual vacuum to ideal vacuum.

10.What are the effects of air leakage in the condenser?

Answers:

1. It increases the back pressure on the turbine with the effect that there is less heat drop and lothermal efficiency of the plant

2. The pressure of air in the condenser lowers the partial pressure of steam, which means steawill condense at a lower temperature and that will require greater amount of cooling water.

3. It reduces the rate of condensation of steam, because air having poor thermal conductivityimpairs the overall heat transfer from the steam-air mixture.

11.What is a steam condenser?

Answers:

1. It is a heat exchanger wherein steam is condensed either in direct contact with cooling waterindirect contact with cooling water through a heat transfer medium separating them.

2. That is, a steam condenser is either a direct contact or indirect contact heat exchanger.12.How many types of steam condensers are known?

Answers:

1. Jet Condensers - direct contact heat exchanger.2. Surface Condensers - indirect contact heat exchanger.

13.What is a surface condenser?

Answer:

It is a shell-and-tube heat exchanger in which steam is condensed on the shell-side while cooling wflows through the tubes. The condensate and cooling water leave the system separately.

14.How does the down-flow type surface condenser act?

Answer:

Exhaust steam is admitted to the top of the condenser, which is a tube-and-shell type crossflow heaexchanger. Cooling water flows through the tubes and extracts heat from the steam, which is on theshell-side. Mter having been condensed on the surface of the water tubes, steam is converted intocondensate which is discharged from the condenser bottom.

15.How does the central flow type surface condenser work?

Answer:

It is also a shell-and-tube type crossflow heat exchanger at the center of which is located the suctionan air extraction pump, so that the entire steam moves radially inward and comes in better contact w

the outer surface of the nest of tubes through which the cooling water flows. The steam condensate extracted from the bottom by the condensate-extraction pump.


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Answers:

1. It is a direct contact heat exchanger in which steam to be condensed comes into direct contawith the cooling water (cold condensate) which is usually introduced in the form of a spray fro

jet. (Fig. 30.1)2. Upon contact with the cooling water, the steam gives up its enthalpy and gets cooled and

ultimately settles as condensate.24.What is a surface condenser?

Answer:

It is a shell-and-tube heat exchanger in which steam is condensed on the shell-side while cooling wflows through the tubes. The condensate and cooling water leave the system separately.

25.How many types of jet condensers are known?

Answers:

1. Parallel flow jet type condenser- It is a kind of jet condenser in which both exhaust steam cooling water enter the condenser at the top, both flow downward and the steam condensatedischarges out from the bottom of the condenser. (Fig. 30.2)

2. Contra flow type jet condenser- The cooling fluid (cold condensate) and exhaust steam floa counter-current direction - steam goes up and cold condensate rains down.

3. Ejector type jet condenser- It is one kind of jet condenser in which the mixing of cooling waand steam takes place in a series of combining cones and the kinetic energy of the steam isexpended to drain off the condensate and cooling water from the condenser. Cooling water isforced through a series of cones and gets mixed with steam coming through ports. As the coowater flows through the series of nozzles, it suffers more and more pressure drop and at thesame time its velocity gradually increases. Due to this pressure drop, more and more steam i

drawn through the ports, gets intimately mixed with the cooling water jet and condensesthereafter.

26.What is the principle of operation of a high-level-parallel-flow jet condenser?

Answer:

This condenser, also called barometric condenser, works as follows - The condenser is mounton a long pipe (at least 10.34 m) called barometric leg which acts in a way identical to a barometer. if water is used in a barometer then the barometric height would be 10.34 m. If some vacuum exists the condenser, the height of water column (h) will be less than 10.34 in. Now it is possible, by using condenser leg, to drain away the condensate from the condenser.

27.How many types of surface condensers are known?

Answers:

1. Down flow type - Exhaust steam is admitted to the top of the condenser, which is a tube-andshell type cross flow heat exchanger. Cooling water flows through the tubes and extracts heafrom the steam which is on the shell-side. After having been condensed on the surface of thewater tubes, steam is converted into condensate, which is discharged from the condenserbottom. (Fig. 30.7)

2. Central flow type - It is also a shell-and-tube type cross flow heat exchanger at the center of

which is located the suction of an air extraction pump so that the entire steam moves radiallyinward and comes in better contact with the outer surface of the nest of tubes through which t


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cooling water flows. The steam condensate is extracted from the bottom by the condensate-extraction pump.

3. Inverted flow type - In this type of condenser, steam is admitted at the bottom and flowsupwards in cross-flow with the cooling water flowing in the tubes. The air extraction pump draits suction from the top of the condenser, maintaining a steady upward current of steam, whicafter having been condensed on the outer surface of water tubes is removed by the condensaextraction pump.

4. Evaporative condenser type - Exhaust steam from the turbine is condensed inside the finnetubes as cooling water rains down from the top through the nozzles. A part of the cooling watcontact with the tube surface evaporates by drawing enthalpy from the steam, which upon los

its latent heat condenses and discharges out as condensate.28.Where is the evaporative condenser used in practice?

Answers:

In those cases where the shortage of cooling water is acute.

29.What are the two prime functions of a condenser?

Answers:

1. It reduces the backpressure upon the turbine by a considerable degree and therefore, the wodone per kg of steam during expansion is increased.

2. The exhaust steam condensate can be recycled as boiler feedwater.30.What are the auxiliary equipment required for operating a steam condenser?

Answers:

1. Cooling water (which may be cold condensate) circulation pump. Generally, it is a centrifugal2. Arrangement for cooling the condensate (i.e., a heat exchanger) in case the condensate is

recycled to extract heat from the exhaust steam.3. An air pump or steam ejector to remove air and other non-condensing gases from the conde

4. An extraction pump (usually centrifugal) to remove the condensate from the condenser.31.What should be the basic criteria for an efficient steam condenser?

Answer:

1. Maximum amount of steam condensed per unit area of available heat transfer surface.2. Minimum quantity of circulating coolant required.3. Minimum heat transfer surface required per kW capacity.4. Minimum power drawn by the auxiliaries.

32.Why is vacuum maintained in the steam condenser?

Answers:

1. By maintaining a vacuum in the steam condenser, the efficiency of the steam-power plant caincreased as greater the vacuum in the system, greater will be the enthalpy drop of steam.Therefore, more work will be available per kg of steam condensing.

2. Secondly, the non-condensate (air) can be removed from the condensate-steam circuit by puand maintaining a vacuum in the steam side. Therefore, the condensate can be used as boilefeed.

33.What are the advantages of a jet condenser over a surface condenser?

Answers:

1. Simplicity in design.


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2. Lower in manufacturing cost.3. Lower maintenance cost.4. Occupies lesser floor space.5. Requires lesser amount of cooling water.

34.What are the advantages of a surface condenser over a jet condenser?

Answers:

1. It imparts to power generation plant a higher thermal efficiency.2. The condensate can be reused as boiler feedwater.

3. Auxiliary power requirement is less than that of a jet condenser.4. Less amount of air is carried to the boiler.

35.What are the limitations of a surface condenser?

Answers:

1. It is very bulky and as such requires more floor space.2. Its manufacturing, running and maintenance costs are high.

36.What should be the requirements of an ideal surface condenser used for steam power plants

Answers:

1. Uniform distribution of exhaust steam throughout the heat transfer surface of the condenser.2. Absence of condensate subcooling.3. There should not be any leakage of air into the condenser.4. There should not be any tube leakage.5. The heat transfer surface in contact with cooling water must be free from any deposit as scal

reduces the efficiency of heat exchangers.37.What do you mean by vacuum?

Answer:

Vacuum means any pressure below atmospheric pressure.

38.How is vacuum in a condenser usually measured?

Answers:

It is measured by means of a Bourdon pressure gauge, which is calibrated to read the pressure in mmercury below atmospheric pressure.

39.If the gauge pressure of a condenser is 630 mm of Hg, what will be the absolute pressure in tcondenser?

Answer:

It means the pressure in the condenser is 630 mm below atmospheric pressure. The atmosphericpressure is 760 mm of Hg, the absolute pressure in the condenser.

40.On what factors does the degree of vacuum in a condenser depend?

Answer:

It depends on the partial pressure of steam and the partial pressure of air in the condenser.

41.How could air enter the condenser?


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Answers:

1. With the boiler feedwater as dissolved gases.2. Flange leakage.3. Cooling water (for jet condenser) containing a certain amount of dissolved air in it.

42.What are the effects of air leakage in the condenser?

Answers:

1. It increases the backpressure on the turbine with the effect that there is less heat drop and lo

thermal efficiency of the plant.2. The pressure of air in the condenser lowers the partial pressure of steam, which means stea

will condense at a lower temperature and that will require greater amount of cooling water.3. It reduces the rate of condensation of steam, because air having poor thermal conductivity

impairs the overall heat transfer from the steam-air mixture.43.What basic governor troubles are apt to occur?

Answers:

1. Hunting-alternate speeding and slowing of the engine, which means that the governor is toosensitive to load changes.

2. Sticking-failure to control speed, allowing the engine to run away or slow down-which meansthe governor is not sensitive to load changes or parts are binding or worn.

44.What is a governor safety stop?

Answers:

On throttling-type governors, the safety stop is a weighted arm that needs the support of a governorIf the belt breaks, the idler arm drops and shuts the steam supply valve to the engine. On Corliss unthe flyballs fall to the lowest position and knock off the safety cams; the cams disengage the catchblocks on the steam intake valves so that no steam is admitted to the engine.

45.Why is condensation or excessive carryover dangerous to reciprocating engines?

Answer:

Because water is non-compressible. If an excessive amount of water gets into the cylinder, it will wrthe engine.

46.Why should a steam or moisture separator be installed in the steam line next to a steam turb

Answer:

All multistage turbines, low-pressure turbines, and turbines operating at high pressure with saturatedsteam should have a moisture separator in order to prevent rapid blade wear from water erosion.

47.Under what conditions may a relief valve not be required on the exhaust end of a turbine?

Answer:

If the manufacturer has provided that the turbine shells are constructed for full-inlet steam pressure the entire length of the shell. It is absolutely essential to have a relief valve to protect the shell in theevent an exhaust valve is closed and high-pressure steam is admitted to the shell on the front end omachine. Explosions have occurred when this happened.

48.What are some conditions that may prevent a turbine from developing full power?


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Answers:

1. The machine is overloaded.2. The initial steam pressure and temperature are not up to design conditions.3. The exhaust pressure is too high.4. The governor is set too low.5. The steam strainer is clogged.6. Turbine nozzles are clogged with deposits.7. Internal wear on nozzles and blades.

49.Why is it necessary to open casing drains and drains on the steam line going to the turbine w

a turbine is to be started?.

Answers:

To avoid slugging nozzles and blades inside the turbine with condensate on start-up; this can breakthese components from impact. The blades were designed to handle steam, not water.

50.What three methods are used to restore casing surfaces that are excessively eroded?

Answers:

1. Metal-spraying.2. Welding.3. Insertion of filler strips or patch plates. The manufacturer should be consulted on the metallur

involved so that the best method can be selected.51.What is steam rate as applied to turbo-generators?

Answer:

The steam rate is the pounds of steam that must be supplied per kilowatt-hour of generator output asteam turbine inlet.

52.What is the most prevalent source of water induction into a steam turbo-generator?

Answer:

Leaking water tubes in feedwater heaters, which have steam on the shell side supplied from turbineextraction lines. The water at higher pressure can flow back into the turbine because the extractionsteam is at a lower pressure. Check valves are needed on the steam extraction line to prevent the bflow of water into the turbine.

53.What is a regenerative cycle?

Answer:

In the regenerative cycle, feedwater is passed through a series of feed-water heaters and is heated steam extracted from stages of a steam turbine. This raises the feedwater to near the temperature oboiler water, thus increasing the thermal efficiency of the cycle.

54.What is the re-heating cycle?

Answer:

In the re-heating cycle, superheated steam is expanded in a high-pressure turbine and then returne

the boiler's re-heater to raise the temperature of the steam to the inlet temperature, usually to aroun537C; it is then returned to the turbine to be expanded through intermediate-pressure turbines. In s


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cases, the steam is again returned for re-heating in the boiler and then expanded in the lower-presssections of the turbine. The main purpose of re-heating the steam on large turbo-generators is to avcondensation in the lower-pressure sections of the turbine, which can rapidly cause blade erosionproblems from wet steam.

55.What does the Willans line show?

Answer:

The Willians line is a plot of throttle flow versus the load, usually expressed in kilowatts; generally it

straight line except for low and high loads. The Willians line is used to show steam rates at differentloads on the turbine.

56.What are the two basic types of turbines?

Answer:

1. Impulse type.2. Reaction type.

57.What is the operating principle of an impulse turbine?

Answer:

The basic idea of an impulse turbine is that a jet of steam from a fixed nozzle pushes against the rotblades and impels them forward. The velocity of the steam is about twice as fast as the velocity of thblades. Only turbines utilizing fixed nozzles are classified as impulse turbines.

58.What is the operating principle of a reaction turbine?

Answer:

A reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. Actually, the steam is

directed into the moving blades by fixed blades designed to expand the steam. The result is a smallincrease in velocity over that of the moving blades. These blades form a wall of moving nozzles thatfurther expand the steam. The steam flow is partially reversed by the moving blades, producing areaction on the blades. Since the pressure drop is small across each row of nozzles (blades), the spis comparatively low. Therefore, more rows of moving blades are needed than in an impulse turbine

59.What are topping and superposed turbines?

Answer:

Topping and superposed turbines arc high-pressure, non-condensing units that can be added to an

older, moderate-pressure plant. Topping turbines receive high-pressure steam from new high-pressboilers. The exhaust steam of the new turbine has the same pressure as the old boilers and is used supply the old turbines.

60.What is an extraction turbine?

Answer:

In an extraction turbine, steam is withdrawn from one or more stages, at one or more pressures, forheating, plant process, or feedwater heater needs. They are often called "bleeder turbines."

61.What is a radial-flow turbine?


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Answer:

In a radial-flow turbine, steam flows outward from the shaft to the casing. The unit is usually a reactiunit, having both fixed and moving blades. They are used for special jobs and are more common toEuropean manufacturers, such as Sta-Laval (now ABB).

62.What is a stage in a steam turbine?

Answer:

In an impulse turbine, the stage is a set of moving blades behind the nozzle. In a reaction turbine, earow of blades is called a "stage." A single Curtis stage may consist of two or more rows of movingblades.

63.What is a diaphragm?

Answer:

Partitions between pressure stages in a turbine's casing are called diaphragms. They hold the vaneshaped nozzles and seals between the stages. Usually labyrinth-type seals are used. One-half of thdiaphragm is fitted into the top of the casing, the other half into the bottom.

64.What are four types of turbine seals?

Answers:

1. Carbon rings fitted in segments around the shaft and held together by garter or retainer sprin2. Labyrinth mated with shaft serrations or shaft seal strips.3. Water seals where a shaft runner acts as a pump to create a ring of water around the shaft. U

only treated water to avoid shaft pitting.4. Stuffing box using woven or soft packing rings that are compressed with a gland to prevent

leakage along the shaft.

65.In which turbine is tip leakage a problem?

Answer:

Tip leakage is a problem in reaction turbines. Here, each vane forms a nozzle; steam must flow throthe moving nozzle to the fixed nozzle. Steam escaping across the tips of the blades represents a loswork. Therefore, tip seals are used prevent this.

66.What are two types of clearance in a turbine?

Answer:

1. Radial - clearance at the tips of the rotor and casing.2. Axial - the fore-and-aft clearance, at the sides of the rotor and the casing.

67.What are four types of thrust hearings?

Answer:

1. Babbitt-faced collar bearings.2. Tilting pivotal pads.3. Tapered land bearings.4. Rolling-contact (roller or ball) bearings.

68.What is the function of a thrust bearing?


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Answer:

Thrust bearings keep the rotor in its correct axial position.

69.What is a balance piston?

Answer:

Reaction turbines have axial thrust because pressure on the entering side is greater than pressure othe leaving side of each stage. To counteract this force, steam is admitted to a dummy (balance) pis

chamber at the low-pressure end of the rotor. Some designers also use a balance piston on impulseturbines that have a high thrust. Instead of piston, seal strips are also used to duplicate a piston'scounter force.

70.What is a combination thrust and radial bearing?

Answer:

This unit has the ends of the babbitt bearing extended radially over the end of the shell. Collars on throtor face these thrust pads, and the journal is supported in the bearing between the thrust collars.

71.What is a tapered-land thrust bearing?

Answer:

The babbitt face of a tapered-land thrust bearing has a series of fixed pads divided by radial slots. Tleading edge of each sector is tapered, allowing an oil wedge to build up and carry the thrust betweethe collar and pad.

72.What is important to remember about radial bearings?

Answer:

A turbine rotor is supported by two radial bearings, one on each end of the steam cylinder. Thesebearings must be accurately aligned to maintain the close clearance between the shaft and the shafseals, and between the rotor and the casing. If excessive bearing wear lowers the he rotor, great hacan be done to the turbine.

73.What is gland-sealing steam?

Answer:

It is the low-pressure steam that is led to a sealing gland. The steam seals the gland, which may be

either a carbon ring or labyrinth type against air at the vacuum end of the shaft.

74.What is the function of a gland drain?

Answer:

The function of a gland drain is to draw of water from sealing-gland cavities created by the condensof sealing steam.

75.What is an air ejector?

Answer:


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An air ejector is a steam siphon that removes non-condensable gases from the condenser.

76.How many governors are needed for safe turbine operation? Why?

Answer:

Two independent governors are needed for safe turbine operation. One is an overspeed or emergentrip that shuts off the steam at 10 percent above running speed (maximum speed). The second, or mgovernor, usually controls speed at a constant rate; however, many applications have variable speecontrol.

77.How is a flyball governor used with a hydraulic control?

Answer:

As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to oppilot valve that admits and releases oil on either side of a piston or on one side of a spring-loadedpiston. The movement of the piston controls the steam valves.

78.What is a multi-port governor valve? Why is it used?

Answer:

In large turbines, a valve controls steam flow to groups of nozzles. The number of open valves contrthe number of nozzles in use according to the load. A bar-lift or cam arrangement operated by thegovernor opens and closes these valves in sequence. Such a device is a multi-port valve. Using nozat full steam pressure is more efficient than throttling the steam.

79.What is meant by critical speed?

Answer:

It is the speed at which the machine vibrates most violently. It is due to many causes, such as imbalor harmonic vibrations set up by the entire machine. To minimize damage, the turbine should be hurthrough the known critical speed as rapidly as possible. (Caution, be sure the vibration is caused bycritical speed and not by some other trouble).

80.How is oil pressure maintained when starting or stopping a medium-sized turbine?

Answer:

An auxiliary pump is provided to maintain oil pressure. Some auxiliary pumps are turned by a handcrank; others are motor-driven. This pump is used when the integral pump is running too slowly to

provide pressure, as when starting or securing a medium-sized turbine.

81.Why is it poor practice to allow turbine oil to become too cool?

Answer:

If a turbine oil is allowed to become too cold, condensation of atmospheric moisture takes place in tand starts rust on the polished surfaces of the journal bearings. Condensed moisture my interfere wlubrication.

82.Steam blowing from a turbine gland is wasteful. Why else should it be avoided?

Answer:


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It should be avoided because the steam usually blows into the bearing, destroying the lubrication oilthe main bearing. Steam blowing from a turbine gland also creates condensate, causing undue moisin plant equipment.

83.Besides lubrication, which are two functions of lubricating oil in some turbines?

Answer:

In large units, lube oil cools the bearings by carrying off heat to the oil coolers. Lube oil in some turbalso acts as a hydraulic fluid to operate the governor speed-control system.

84.What is meant by the water rite of a turbine?

Answer:

85.It is the amount of water (steam) used by the turbine in pounds per horsepower per hour orkilowatts per hour.

86.What are five types of condensers?

Answer:

1. Surface (shell-and-tube).2. Jet condenser.3. Barometric condenser.4. Air-cooled condenser.5. Evaporative condenser.

87.Why is there a relief valve on a turbine casing?

Answer:

The turbine casing is fitted with spring-loaded relief valves to prevent damage by excessive steampressure at the low-pressure end if the exhaust valve is closed accidentally. Some casings on smallturbines are fitted with a sentinel valve, which serves only to warn the operator of over-pressure of texhaust end. A spring-loaded relic valve is needed to relieve high pressure.

88.Why must steam turbines be warmed up gradually?

Answer:

Although it is probable that a turbine can, if its shaft is straight, be started from a cold condition witho

warming up, such operation does not contribute to continued successful operation of the unit. Thetemperature strains set up in the casings and rotors by such rapid heating have a harmful effect. Theturbine, in larger units especially should be warmed slowly by recommended warm-up ramp ratesbecause of close clearances.

89. What should you lost vacuumwhile operating a condensing turbine plant?

Answer:

If vacuum is lost shut down immediately. The condenser cannot stand steam pressure, the condenstubes may leak from excessive temperature. Excessive pressure will also damage the shell, the exh

and the low-pressure parts of the turbine.


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90.What are the main causes of turbine vibration?

Answers:

1. Unbalanced parts.2. Poor alignment of parts.3. Loose parts.4. Rubbing parts.5. Lubrication troubles.6. steam troubles.

7. Foundation troubles.8. Cracked or excessively worn parts.

91.What is the purpose of a turning gear?

Answer:

Heat must be prevented from warping the rotors of large turbines or high-temperature turbines of 40or more. When the turbine is being shut down, a motor-driven turning gear is engaged to the turbinerotate the spindle and allow uniform cooling.

92.What does he term "ramp" rate mean?

Answer:

Ramp rate is used in bringing a turbine up to operating temperature and is the degrees Celsius rise hour that metal surfaces are exposed to when bringing a machine to rated conditions. Manufacturerspecify ramp rates or their machines in order to avoid thermal stresses. Thermocouples are used inmeasuring metal temperatures.

93.What is the difference between partial and full arc admission?

Answer:

In multi-valve turbine inlets, partial arc ad mission allows the steam to enter per valve opening in asequential manner, so as load is increased, more valves open to admit steam. This can cause unevheating on the high-pressure annulus as the valves are individually opened with load increase. In fuadmission, all regulating valves open but only at a percentage of their full opening. With load increasthey all open more fully. This provides more uniform heating around the high-pressure part of theturbine. Most modern controls start with full-arc and switch to partial arc to reduce throttling lossesthrough the valves.

94.What are some common troubles in surface-condenser operation?

Answer:

The greatest headache to the operator is loss of vacuum caused by air leaking into the surfacecondenser through the joints or packing glands. Another trouble spot is cooling water leaking into thsteam space through the ends of the tubes or through tiny holes in the tubes. The tubes may alsobecome plugged with mud, shells, debris, slime or algae, thus cutting down on the cooling water supCorrosion may be uniform, or it may occur in small holes or pits.

95.Where would you look for a fault if the air ejector didn't raise enough vacuum?

Answers:

1. In this case, the trouble is usually in the nozzle. You will probably find that the nozzle is erode


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2. The strainer protecting the nozzle is clogged.3. The steam pressure to the nozzle is too low.

96.How would you stop air from leaking into a condenser?

Answer:

First find the leak by passing a flame over the suspected part while the condenser is under vacuum.Leaks in the flange joints or porous castings can be stopped with asphalt paint or shellac.

97.Do you stop cooling water flow through a steam condenser as soon as the turbine is stopped

Answer:

You should keep the cooling water circulating for about 15 minutes (also see the manufacturersrecommendation) or more so that the condenser has a chance to cool down gradually and evenly. Bsure to have cooling water flowing through the condenser before starting up in order to prevent steafrom entering the condenser unless it is cooled. Overheating cause severe leaks and other headach

98.How would you stop a leaky tube in a condenser that was contaminating the feed water?

Answer:

To stop leaky tube from contaminating the feedwater, shut down, remove the water-box covers, andthe steam space with water. By observing tube ends, you can find the leaky tube. An alternate methto pressurize (30 kPa) the steam space with air. Then flood the water boxes to the top inspection plaand observe any air bubbles. Once you have found the leaky tube or tubes, drive a tape bronze plug(well-coated with white lead) into each end of the tube to cut it out service. This allows you to use thecondenser since the tubes need not be renewed until about 10 percent of the tubes are plugged.

99.Why must condensate be subjected to salinity tests where brackish cooling water used?

nswer:

ondensate may leak from the cooling-water side to the steam side of condenser and contaminate theedwater, thus causing scale to form in the boilers, brackish cooling water may leak into the steam space

cracked or porous tubes or ruin around the joints at the endthe tube ends, etc. By taking salinity readings of thecondensate, leaks may be found before they can do any ha

STEAM POWER CYCLE

wer plants generate electrical power by using fuels like coal, oil or natural gas. A simple power plant consists of a boiler, turbi


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condenser and a pump. Fuel, burned in the boiler and superheater, heats the wto generate steam. The steam is then heated to a superheated state in thesuperheater. This steam is used to rotate the turbine which powers the generatoElectrical energy is generated when the generator windings rotate in a strongmagnetic field. After the steam leaves the turbine it is cooled to its liquid state incondenser. The liquid is pressurized by the pump prior to going back to the boilesimple power plant is described by a Rankine Cycle.

RANKINE CYCLE

Saturated or superheated steam enters the turbine at state 1, where it expandsisentropically to the exit pressure at state 2. The steam is then condensed at copressure and temperature to a saturated liquid, state 3. The heat removed from steam in the condenser is typically transferred to the cooling water. The saturate

uid then flows through the pump which increases the pressure to the boiler pressure (state 4), where the water is first heated tturation temperature, boiled and typically superheated to state 1. Then the whole cycle is repeated.

YPICAL MODIFICATIONS

EHEAT

hen steam leaves the turbine, it is typically wet. The presense of water causes erosion of the turbine blades. To prevent this, sextracted from high pressure turbine (state 2), and then it is reheated in the boiler (state 2') and sent back to the low pressurebine.

EGENERATION

egeneration helps improve the Rankine cycle efficiency by preheating the feedwater into the boiler. Regeneration can be achieopen feedwater heaters or closed feedwater heaters. In open feedwater heaters, a fraction of the steam exiting a high pressubine is mixed with the feedwater at the same pressure. In closed system, the steam bled from the turbine is not directly mixed

e feedwater, and therefore, the two streams can be at different pressures.

PROPERTIES OF STEAM AND WATER

NTRODUCTION

The process by which we convert water into steam and use the steam to turn a propulsion shaft encompasse

generation and expansion phases of the steam cycle. A study of the properties of water and steam at these cphases is necessary to understand the steam cycle. This lesson defines terms associated with these propertie

processes, and explains the use of steam tables to calculate the work and efficiency created by steam.

EFERENCES

(a) Elements of Applied Thermodynamics, Robert M. Johnson, et al.

(b) Principles of Naval Engineering NAVPERS 10788 series

(c) Introduction to Naval Engineering, Edward F. Gritzen.


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NFORMATION

. Basic Thermodynamic Terms

Enthalpy (h), measured in British thermal units per pound (mass), or BTU/lbm, represents the total energy cont

steam. It expresses the internal energy and flow work, or the total potential energy and kinetic energy cont

within a substance. The advantage ofenthalpy is that we can express in one term all of the energy in a subswhich is due to its pressure and temperature. Enthalpy values are used to represent the energy level of

entering a turbine, a value useful for determining turbine efficiency. By superheating steam, we can add entto steam without raising the pressure of the steam. For example, steam at 620 psig and 850F can do more wa turbine than steam that is 620 psig and 650F.

Entropy (s), measured in BTU/lbm-R, represents the unavailability of energy (R=Rankine temperature scale w

0R = absolute zero and 460R = 0F). The second law of thermodynamics states that when heat is trans

from high temperature to low temperature regions, some of the heat will be rejected and not convertedmechanical work. Entropy is a measure of how much heat must be rejected to a lower temperature receive

given pressure and temperature.

A complex explanation of the mathematical significance of the definition of entropy is unnecessary. It is a

which attempts to describe the universes tendency to evenly distribute all mass and energy throughout sProcesses which produce entropy are possible and those which destroy entropy are impossible.

Bodies with a high temperature will, when brought in contact with a body of a lower temperature, always cause

to transfer from the hot body to the cold body. This will lower the internal energy of the hot body and rai

internal energy of the cold body. This is the principle that guides the design and operation of all navaexchangers. For example, a main engine lube oil cooler directs hot lube oil over cool seawater piping, so th

hot lube oil will transfer some of its heat to the cooler seawater. If left together indefinitely, the proper

entropy would cause the heat from the lube oil to be equally distributed between the oil and the water, so thatwould have the same temperature.

Entropy would not be important except for the fact that the purpose of any engine is to collect, transfer, anenergy. Thus, in a steam plant for example, it is not possible to add energy to water, boil it and transm

resulting high energy steam across the relatively cooler engineroom without some of that energy being lost. of this energy will always be lost through system conditions such as ineffective pipe lagging, piping leaks

dirty or fouled tubes which retard heat transfer. Operators must constantly attempt to minimize the effects of

conditions to maximize plant efficiency and reduce fuel and water costs.

A working fluidis a substance which receives, transfers and transmits energy in a thermodynamic system. Insystems, the working substance is a fluid (liquid, vapor or gas). In a steam system, water is the working fluid

Density (r), measured in lbm/ft, represents the mass of a substance per unit volume, or how tightly packe

molecules are. The more molecules packed in a given space, the more dense the material. The density of waa given location of the boiler is critical to the steam generation process because relatively dense feedwatenaturally push a less dense steam/water mixture through the boiler generating tubes.

Specific volume (vSP), measured in ft3/lbm, represents the space occupied per unit mass of a substance. It

mathematical inverse of density. Most engineering equipment is designed for size and strength taking

consideration the specific volume of the intended working fluid.

Specific weight(g), measured in lbf/ft3, represents the weight of a substance per unit volume. This is the densit

substance acted upon by gravity. The pressure of a fluid at the bottom of a storage tank is a direct function

height of the fluid in the tank and the specific weight of the feedwater. This resultant pressure is an imp

shipboard consideration with respect to providing a minimum suction pressure for a pump below the tank to the fluid through a system.


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7. The state of a working fluid refers to the physical properties it possesses at a particular pressure, temperand volume. If each of these are known with respect to a substance, the state of the substance is known.

substance can be a subcooled, saturated, or superheated solid, liquid, or gas. Many systems operate the wo

fluid with very specific temperature/pressure relationships. Water is subcooled in the condensate and feed pof the steam cycle to allow it to be pumped, saturated in portions of the generation and feed phases for natural

or for maintaining proper chemistry, and superheated in the expansion phase to extract maximum work fro

steam to turn a propulsion turbine.

A thermodynamic process is any process which changes the state of the working fluid. These processes cclassified by the nature of the state change that takes place. Common types of thermodynamic processes in

the following:

A reversible process is an ideal process where the working fluid returns to its original state by conducting the or

process in the reverse direction. For a process to be reversible, it must be able to occur in precisely the reorder. All energy that was transformed or distributed during the original process must be capable of being ret

to its exact original form, amount and location. Reversible processes do not occur in real life.

An irreversible process is any process which is not reversible. All real life processes, such as the basic steam

are irreversible.

An adiabatic process is a state change where there is no transfer of heat to or from the system during the pro

Because heat transfer is relatively slow, any rapidly performed process can approach being adiaCompression and expansion of working fluids are frequently achieved adiabatically with pumps and turbines.

An isothermal process is a state change in which no temperature change occurs. Note that heat transfer can without causing a change in temperature of the working fluid. In the DFT, auxiliary exhaust heats inco

condensate, then condenses to liquid and falls to the bottom of the tank. Throughout this process, the temper

of the auxiliary exhaust remains constant at 246-249F.

An isobaric process is a state change in which the pressure of the working fluid is constant throughout the chAn isobaric state change occurs in the boiler superheater, as the heat of the exiting steam is increased wi

increasing its associated pressure.

A thermodynamic cycle is a recurring series of thermodynamic processes through which an effect is produced b

transformation or redistribution of energy. In other words, it is a series of processes repeated over and over in the same order. Thermodynamic cycles contain five basic elements: (1) a working fluid, (2) an engine,

heat source, (4) a heat receiver, and (5) a pump. All thermodynamic cycles may be classified as being open c

or closed cycles.

A closed cycle is one in which the working fluid is reused. Steam plants and refrigeration cycles are closed cIn a steam plant, the water undergoes a series of processes that change the state of the water. Eventually the w

returns to its original state and is ready to begin the cycle again.

An open cycle is one in which the working fluid is not reused. Open cycles typically use the atmosphereworking fluid. An internal combustion engine represents a typical open cycle. Air is drawn into the encombusted in the cylinders, and exhausted back to the atmosphere. Fresh air is drawn into the engine to beg

cycle again.

. Heat Addition and Temperature

When heat is added to a material, one of two things will occur: the material will change temperature or the mawill change state. When a substance is below the temperature at a given pressure required to change stat

addition ofsensible heatwill raise the temperature of the substance. Sensible heat applied to a pot of wate

raise its temperature until it boils. Once the substance reaches the necessary temperature at a given pressu

change state, the addition of latent heatcauses the substance to change state. Adding latent heat to the bwater does not get the water any hotter, but changes the liquid (water) into a gas (steam).


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One can state that a certain amount of heat is required to raise the temperature of a substance 1F. This enecalled thespecific heat capacity. The specific heat capacity of a substance depends upon the volume and pre

of the material. For water, the specific heat capacity is 1 BTU/lbm-F and remains constant. This means that

add 1 BTU of heat to 1 lbm of water, the temperature will rise 1F.

. Introduction to Steam Tables

When a teapot of water is placed on a hot burner, sensible heat begins to heat the water. The energy added twater raises its internal energy and its temperature. When the water reaches 212F, the temperature no longer

as latent heat begins to change the water from a liquid to a vapor. The mass inside the teapot is slowly cha

from a 100% water / 0% steam mixture into a 0% water / 100% steam mixture. If we add only half the necelatent heat, then only half the water will boil into steam. The result would be a 50% water / 50% steam mixt

212F. If we add all the latent heat necessary, then the water at 212F changes completely into steam at 2

Continuing to add heat to the 212F steam results in a temperature increase (superheating), and we are raising the temperature by adding sensible heat. Refer to figure 3.2-1 (sensible/latent heat and enthalpy).

While the properties of water at atmospheric pressure are commonly known, water under different pressure

exhibit different properties. When water is boiled at pressures higher than atmospheric, the same events occ

described above with two exceptions. First, the boiling temperature will be higher than 212F. Second, less heat is required to be added to change the water completely into steam. If water were to be boiled at a pre

lower than atmospheric pressure, then we would find that the boiling temperature would be less than 212F

larger amount of latent heat would be required to change the water completely into steam. Refer to figure (temperature vs. latent heat).

When water is below the boiling point, the addition of heat is seen as sensible heat. This water is said to

subcooled liquid. When enough sensible heat is added so that the temperature of the water approaches satur

temperature but no steam has yet been formed, the water is said to be asaturated liquid.

As the water is transformed from a saturated liquid to saturated steam, boiling is occurring. As latent heat is athe temperature of the water remains the same but the saturated liquid is being changed into a saturated v

During this period the water is referred to as a liquid/vapor mixture. When enough latent heat is added so th

of the liquid is converted into vapor, the water becomes a saturated vapor. Note that the saturated vapor is

vapor and exists at the same temperature as the saturated liquid. Above the saturated steam point, vapor existemperature higher than saturation temperature. This is thesuperheated vaporregion.

Steam tables are a useful tool for determining the properties of steam and water at various temperature

pressures. The steam tables are broken into three tables.

Mollier Diagram

The Mollier diagram is a small portion of data from the steam tables graphed onto enthalpy-entropy coordinat

presents the region that is commonly found in propulsion plant steam systems. Examine the last section osteam tables for a representation of a Mollier diagram.

Locating information off the Mollier diagram is done as follows: The horizontal axis is entropy (s) in BTU/lbm

The vertical axis is enthalpy (h) in BTU/lbm. The dark line across the middle of the chart is called a steam d

because of its shape. Above this line, the data is for superheated steam. Below this line, the data is for a s

water mixture. The data directly on the line is for saturated steam.

To find data in the steam-water mixture region of the chart, enter the chart using the absolute pressure an

moisture (y). Once you find the intersection of these two parameters, read off the number directly across fro

intersection point for enthalpy. Read off the number directly below the intersection point for entropy.


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o find data in the superheated region of the chart, enter the chart using the measured temperature and pressure osteam. Again, find the intersection point of these two parameters and read off the values for entropy and enth

Notice that moisture does not plot in the superheat region. This is because moisture is a parameter which

exists in saturated conditions.

How Gas Turbine Work

Little Background

here are many different kinds of turbines:

You have probably heard of a steam turbine. Most power plants use coal, natural gas, oil or a nuclereactor to create steam. The steam runs through a huge and very carefully designed multi-stage turto spin an output shaft that drives the plant's generator.

Hydroelectric dams use water turbines in the same way to generate power. The turbines used in ahydroelectric plant look completely different from a steam turbine because water is so much denser slower moving) than steam, but it is the same principle.

Wind turbines, also known as wind mills, use the wind as their motive force. A wind turbine looksnothing like a steam turbine or a water turbine because wind is slow moving and very light, but againprinciple is the same.

gas turbine is an extension on the same concept. In a gas turbine a pressurized gas spins the turbine. Inodern gas turbine engines the engine produces its own pressurized gas, and it does this by burningmething like propane, natural gas, kerosene or jet fuel. The heat that comes from burning the fuel expan

r, and the high-speed rush of this hot air spins the turbine.

dvantages and Disadvantages of Gas Turbine Engines

o why does the M-1 tank use a 1,500 horsepower gas turbine engine instead of a diesel engine? It turns oat there are two big advantages:

1. Gas turbine engines have a great power-to-weight ratio compared to reciprocating engines. That isamount of power you get out of the engine compared to the weight of the engine itself is very good.

2. Gas turbine engines are also smaller than their reciprocating counterparts of the same power.

he main disadvantage of gas turbines is that, compared to a reciprocating engine of the same size, they axpensive. Because they spin at such high speeds and because of the high operating temperatures, designd manufacturing gas turbines is a tough problem from both the engineering and materials standpoint. Garbines also tend to use more fuel when they are idling and they prefer a constant load rather than actuating load. That makes gas turbines great for things like trans-continental jet aircraft and power plants

xplains why you don't have one under the hood of your car.

ow Gas Turbine Engines Work

as turbine engines are, theoretically, extremely simple. They have 3 parts:

A compressor to compress the incoming air to high pressure. A combustion area to burn the fuel and produce high pressure, high velocity gas. A turbine to extract the energy from the high pressure, high velocity gas flowing from the combustio

chamber.

he following figure shows the general layout of an axial-flow gas turbine - the sort of engine you would findiving the rotor of a helicopter, for example:


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this engine air is sucked in from the right by the compressor. The compressor is basically a cone-shapedlinder with small fan blades attached in rows (8 rows of blades are represented here). Assuming the lighue represents air at normal air pressure, then as the air is forced through the compression stage its pressnd velocity rise significantly. In some engines the pressure of the air can rise by a factor of 30. The high-essure air produced by the compressor is shown in dark blue.

his high-pressure air then enters the combustion area, where a ring of fuel injectors injects a steady streael. The fuel is generally kerosene, jet fuel, propane, or natural gas. If you think about how easy it is to blondle out, then you can see the design problem in the combustion area - entering this area is high-pressu

r moving at hundreds of miles per hour. You want to keep a flame burning continuously in that environmehe piece that solves this problem is called a "flame holder", or sometimes a "can". The can is a hollow,erforated piece of heavy metal (shown here is half of the can in cross-section):

he injectors are at the right. Compressed air enters through the perforations. Exhaust gases exit at the lefou can see in the previous figure that a second set of cylinders wraps around the inside and the outside os perforated can, guiding the compressed intake air into the perforations.

the left of the engine is the turbine section. In this figure there are two sets of turbines. The first set direcives the compressor. The turbines, the shaft and the compressor all turn as a single unit:


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the far left is a final turbine stage, shown here with a single set of vanes. It drives the output shaft. This frbine stage and the output shaft are a completely stand-alone, freewheeling unit. They spin freely withounnection to the rest of the engine. And that is the amazing part about a gas turbine engine - there is enou

nergy in the hot gases blowing through the blades of that final output turbine to generate 1,500 horsepownd drive a 63 ton M-1 Tank! A gas turbine engine really is that simple.

the case of the turbine used in a tank or a power plant, there really is nothing to do with the exhaust gaseut vent them through an exhaust pipe, as shown. Sometimes the exhaust will run through some sort of hexchanger either to extract the heat for some other purpose or to preheat air before it enters the combustioamber.

he discussion here is obviously simplified a bit. For example, we have not discussed the areas of bearinging systems, internal support structures of the engine, stator vanes and so on. All of these areas becomeajor engineering problems because of the tremendous temperatures, pressures and spin rates inside the

ngine. But the basic principles described here govern all gas turbine engines and help you to understand asic layout and operation of the engine.

ther variations

arge jetliners use what are known as turbofan engines, which are nothing more than gas turbines combinth a large fan at the front of the engine. Here's the basic (highly simplified) layout of a turbofan engine:

ou can see that the core of a turbofan is a normal gas turbine engine like the one described in the previouction. The difference is that the final turbine stage drives a shaft that makes it's way back to the front of th

ngine to power the fan (shown in red in this picture). This multiple concentric shaft approach, by the way, xtremely common in gas turbines. In many larger turbofans, in fact, there may be two completely separatempression stages driven by separate turbines, along with the fan turbine as shown above. All three shaf

e within one another concentrically.

he purpose of the fan is to dramatically increase the amount of air moving through the engine, and therefocrease the engine's thrust. When you look into the engine of a commercial jet at the airport, what you sees fan at the front of the engine. It is huge (on the order of 10 feet in diameter on big jets), so it can move air. The air that the fan moves is called "bypass air" (shown in purple above) because it bypasses the tur

ortion of the engine and moves straight through to the back of the nacelle at high speed to provide thrust.

turboprop engine is similar to a turbofan, but instead of a fan there is a conventional propeller at the frone engine. The output shaft connects to a gearbox to reduce the speed, and the output of the gearbox turne propeller.


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simple gas turbine is comprised of three main sections a compressor, a combustor, and a porbine. The gas-turbine operates on the principle of the Brayton cycle, where compressed air iixed with fuel, and burned under constant pressure conditions. The resulting hot gas is alloweexpand through a turbine to perform work. In a 33% efficient gas-turbine approximately two /irds of this work is spent compressing the air, the rest is available for other work ie.( mechani

rive, electrical generation)

However there are variations...

ne variation of this basic cycle is the addition of a regenerator. A gas-turbine with a regeneraeat exchanger) recaptures some of the energy in the exhaust gas, pre-heating the air enterine combustor. This cycle is typically used on low pressure ratio turbines.

Turbines using this cycle are: Solar Centaur/ 3500 horsepower classup to the General Electric Frame 5


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as-turbines with high pressure ratios can use an intercooler to cool the air between stages ofompression, allowing you to burn more fuel and generate more power. Remember, the limitingctor on fuel input is the temperature of the hot gas created, because of the metallurgy of the fage nozzle and turbine blades. With the advances in materials technology this physical limit i

ways climbing.

One turbine using this cycle is: General Electric LM1600 / Marine version

gas-turbine employing reheat.


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An Intercooled & Recuperated Turbine

GAS-TURBINE HISTORY

The history of the gas turbine begins with a qufor jet propulsion.

The earliest example of jet propulsion can betraced as far back as 150 BCto an EgyptiannamedHero. Hero invented a toy that rotatedtop of a boiling pot due to the reaction effect ohot air or steam exiting several nozzles arrangradially around a wheel. He called this inventio

an aeolipile.

In 1232 the Chinese used rockets to frightenenemy soldiers.

round1500A.D. Leonardo da Vincidrew a sketch of a device that rotated due to the effect oot gasses flowing up a chimney. The device was intended to be used to rotate meat beingasted. In 1629 another Italian namedGiovanni Branca actually developed a device that usets of steam to rotate a turbine that in turn was used to operate machinery. This was the firstractical application of a steam turbine.


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Ferdinand Verbiesta Jesuit inChina built a model carriage thatused a steam jet for power in 167

The first patent for a turbine enginwas granted in 1791 to anEnglishman namedJohn Barberincorporated many of the sameelements of a modern gas turbine

sed a reciprocating compressor. There are many more early examples of turbine enginesesigned by various inventors, but none were considered to be true gas turbines because theycorporated steam at some point in the process.

1872a man by the name ofStolze designed the first true gas turbine. His engine incorporatultistage turbine section and a multi stage axial flow compressor. He tested working models ie early1900's.

harles Curtis the inventor of the Curtis steam engine filed the first patent application in the Ur a gas turbine engine. His patent was granted in 1914 but not without some controversy.

he General Electric company started their gas turbine division in 1903. An engineer namedtanford Moss lead most of the projects. His most outstanding development was the General

lectric turbosupercharger during world war 1. ( Although credit for the concept is given to Ratef France.) It used hot exhaust gasses from a reciprocating engine to drive a turbine wheel tharn drove a centrifugal compressor used for supercharging. The evolutionary process ofrbosupercharger design and construction made it possible to construct the first reliable gasrbine engines.

r Frank Whittle of Great Britain patented a design for a jet aircraft engine in 1930.He firstoposed using the gas turbine engine for propulsion in 1928 while a student at the Royal Air

orce College in Cramwell, England. In 1941 an engine designed by Whittle was the firstuccessful turbojet airplane flown in Great Britain.

oncurrently with Whittle's development efforts, Hans von Ohain and Max Hahn, two students ottingen in Germany developed and patented their own engine design in 1936 these ideas wedapted by The Ernst Heinkel Aircraft company. The German Heinkelaircraft company is credith the first flight of a gas turbine powered jet propelled aircraft on August 27th 1939.The HEas the first jet airplane to fly.

he Heinkel HeS-3b developed 1100 lbs. of thrust and flew over 400 mph, later came the ME2500 mph fighter, more than 1600 of these were built by the end of WWII. These engines wereore advaced than the British planes and had such features as blade cooling and a variable ar

xhaust nozzles.


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1941Frank Whittle began flight tests of a turbojet engine of his own design in England.ventually The General Electric company manufactured engines in the U.S. based on Whittle'sesign.

que & ans other than turbine

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