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Turbines (Steam, Gas and Water) Flashcards

1
Q

How are gas turbines classified on combustion process ?

A

Constant Volume

Constant Pressure

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2
Q

How are gas turbines classified on action of expanding gases ?

A

Impulsive forces

Impulsive-Reactive force

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3
Q

How are gas turbines classified on working path of gases ?

A

Open cycle gas turbine

Closed cycles gas turbine

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4
Q

How are gas turbines classified on direction of flow ?

A

Axial

Radial

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5
Q

What is axial flow ?

A

Flow of working fluid is parallel to axis of shaft

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6
Q

What is radial flow ?

A

Flow of working fluid is in direction of radius

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7
Q

How are gas turbines classified on shaft configuration ?

A

Single shaft

Multiple Shaft

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8
Q

How are gas turbines classified on thermodynamic cycle ?

A

Simple cycle
Simple cycle with regenerator
Simple cycle with re-heat

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9
Q

How are gas turbines classified on basis of application ?

A

Aviation

Industrial

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10
Q

What are the three main components of open cycle gas turbines ?

A

Compressor
Combustion Chamber
Gas turbine

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11
Q

What is the function of the compressor ?

A

It draws air from the atmosphere and compresses it to high pressure adiabatically

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12
Q

What is an adiabatic process ?

A

A process that occurs without transfer of heat or matter between a system and it’s surroundings.

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13
Q

What happens in the combustion chamber ?

A

Fuel is injected into the high pressure air and combustion takes place. The temperature of the air increases at constant pressure

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14
Q

What happens in the gas turbine ?

A

The product of the combustion chamber is expanded on the turbine blade adiabatically.

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15
Q

What happens to the thermal energy of the gas ?

A

It is extracted by the turbine and converted to power

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16
Q

Why are the turbine and compressor mechanically coupled via a shaft ?

A

Some energy is used to turn a shaft to drive the compressor

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17
Q

Why are closed cycle gas turbines smaller than open cycle gas turbines ?

A

High density working fluid is used

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18
Q

Which gas turbine has a greater thermal efficiency ?

A

Closed cycle gas turbines have a greater thermal efficiency for the same range of temperatuer

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19
Q

Why is there less corrosion in closed cycle gas turbines ?

A

Working fluid is not contaminated because of indirect heating.

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20
Q

How is the working fluid contaminated in open cycle gas turbines ?

A

Fuel combustion

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21
Q

Which turbine offers a greater output ?

A

Closed cycle gas turbines have a greater output per unit weight of turbine

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22
Q

What is the reason expensive fuels are used in open cycle gas turbines ?

A

Fuel comes in contact with working medium and should not contaminate it.

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23
Q

Why are closed cycle gas turbines not suitable for avionics ?

A

They need cooling water or a coolant to remove heat

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24
Q

Why is heat transfer efficiency lower in closed cycle gas turbines ?

A

Heat is transfered indirectly and higher heat transfer area is required

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25
What kind of heat exchangers required in closed cycle gas turbines ?
Complicated heat exchangers
26
Why does the closed cycle gas turbine need to be perfectly sealed ?
The working medium should not leak.
27
Do gas turbines have a greater thermal efficiency than IC Engines ?
Yes, because they do not have any reciprocating component.
28
What is the reason gas turbines can be operated at a much higher speed than IC engines ?
They are better balanced.
29
Why are they better balanced ?
There is no reciprocating component.
30
Why can cheaper fuels be used in gas turbines than in IC engines ?
External combustion
31
Why are gas turbines more suited to avionics application than IC engines ?
Lower specific weight and higher reliability.
32
Why are gas turbines less polluting than IC engines ?
External combustion means higher air to fuel ratio
33
Do gas turbines have a higher thermal efficiency than IC engines ?
No, IC engines have a (15-20%) higher thermal efficiency
34
Why do gas turbines require speed reduction gear box ?
It operates at higher speeds
35
Which is hard to start ?
Gas turbines
36
Which has simpler lubrication and ignition system ?
Gas turbines have a simpler lubrication system and ignition system
37
Why is blade fabrication for gas turbines harder ?
High strength Nickel chromium alloys
38
How much AMOUNT of exhaust gases do gas turbines produce ?
About five times as much as IC Engines for the same output power
39
Why does gas turbine cooling need more elaborate arrangement, even though it need less cooling than IC Engines ?
The cooling has to be done to the blades
40
How are gas turbines lighter than steam turbines ?
They do not need bulky and expensive boiler with their mountings and accessories
41
Are gas turbines more expensive than steam turbines ?
No, they have less initial and operating cost
42
Which has higher reliability ?
Gas turbines are more reliable than steam turbines
43
Which turbines are easier to start and control ?
Gas Turbines
44
How is the fuel more efficiently used in gas turbines ?
The fuel drives the turbine directly without producing an intermediate fluid like steam.
45
Where are gas turbines widely used ?
Aerospace like turbo jet, turbo-propellor and rocket engines
46
What kind of plants are they used in ?
Peak load supplementary plants, central power station and high power pumping station
47
How are water turbines classified based on head and Quantity of water available ?
High Medium Low
48
What is the maximum head available for high head turbines ?
400m
49
What is an example of high head turbine ?
Pelton
50
What is the range of head available for medium head turbine ?
60-400m
51
What is an example of medium head turbine ?
Francis turbine is a medium head turbine
52
What is the range of low head turbines ?
3-400m
53
How are water turbines classified based on nature of water interaction ?
Impulse | Reaction
54
What is an impulse turbine ?
Pressure of water does not change while flowing through the rotor
55
What is a reaction turbine ?
Pressure of water changes while flowing through rotor
56
What is an example of impulse turbine ?
Pelton wheel turbine
57
What is an example of reaction turbine ?
Francis or Kaplan turbine
58
What are water turbines classified based on nature of water flow ?
Radial Tangential Axial Mixed
59
What happens in radial flow turbines ?
Water flows from inlet to outlet of rotor along radius
60
What is an example of radial flow turbine ?
Initial Francis turbine
61
What happens in tangential flow turbines ?
Water flows tangential to runner
62
What is an example of tangential flow turbine ?
Pelton wheel turbine
63
What is a mixed flow turbine ?
Water enter rotor radially, but exits axially
64
What is an example of mixed flow turbine ?
Modern Francis turbine
65
What is an axial flow turbine ?
Water flows parallel to axis of turbine shaft
66
What is an example of axial flow turbine ?
Kaplan turbine
67
How are water turbines classified based on orientation of shaft ?
Horizontal | Vertical
68
Which turbine, in modern day practice, has a horizontal shaft ?
Pelton
69
How is specific speed of a water turbine defined ?
It is the speed of geometrically similar turbine which will develop one brake power using 1 meter head of water
70
What is the speed of Pelton turbine ?
10 to 35
71
What is the speed of Francis turbine ?
60-300
72
What is the speed of Kaplan turbine ?
300 to 1000
73
How are water turbines classified based on originator ?
Pelton Francis Kaplan
74
What kind of a turbine is Pelton turbine ? (Basic characteristics)
Impulse, high head - low discharge
75
What kind of a turbine is Francis turbine ?
Reaction, medium to low head
76
What kind of turbine is Kaplan turbine ?
Reaction, low head, high quantity of water flow
77
What kind of vanes do Francis turbines use ?
Moving, non adjustable vanes
78
What kind of vanes do Kaplan turbines use ?
Adjustable with governing mechanism
79
What kind of a governor does a Francis turbine use ?
Simple governor
80
What kind of a governor does a Kaplan turbine use ?
Heavy duty governor
81
Why do Kaplan turbines use heavy duty governor ?
It governs both the flow of water and movement of vanes
82
How many vanes do Francis turbines have ?
16 to 24
83
How many blades to Kaplan turbines have ?
3 to 8 blades
84
What kind of flow rate does Francis turbine deal with ?
Average
85
What kind of flow rate does Kaplan turbine deal with ?
High flow rate
86
What is the maximum head of Kaplan turbine ?
30m
87
What are the five main parts of a Pelton wheel turbine ?
``` Wheel Bucket Nozzle with controller Auxiliary jet Casing ```
88
What is wheel ?
The rotating disc mounted of the shaft
89
How are the buckets and wheel casted in large power plants ?
They are casted together
90
Why ?
This provides high power and efficiency
91
How are they casted in medium power plants ?
Seperately
92
How are buckets and the wheel casted in medium to small power plants ?
By nuts and bolts
93
Where are the buckets uniformly fixed ?
On the periphery of the disc
94
What are the buckets made up of ?
Stainless steel

Mechanical Engineering (8 decks)

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