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TMMV12 > Gas Turbine Systems > Flashcards

Gas Turbine Systems Flashcards

1
Q

What is the simple definition of a gas turbine?

A

An internal combustion engine consisting of an air compressor, a combustor chamber and a turbine.

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2
Q

What are the assumptions for the ideal simple gas turbine cycle?

A
  • Steady processes
  • Isentropic compression and expansion
  • No pressure loss
  • Constant specific heat and specific heat ratio
  • Working fluid is ideal gas
  • Added amount of fuel is neglected in energy balance relations
  • Efficiencies for compression and expansion are unity
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3
Q

What does the first law of thermodynamics state?

A

The energy flowing into a system equals the energy flow out of the system

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4
Q

What forms can the conversed energy from first law of thermodynamics show up as?

A

Chemical energy
Kinetic energy
Potential energy
Mechanical energy
Heat

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5
Q

What is the key to high thermal efficiency and high specific work output?

A

Thermal: high pressure ratio
Work: high turbine inlet temperature

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6
Q

What are the types of industrial gas turbines?

A
  • Single shaft engine
  • Multiple shaft engine
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7
Q

What is a gas generator?

A

The compressor, the combustion chamber and the turbine makes the gas generator

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8
Q

What are numbering of stations used for?

A

Keeping track of the different components in a gas turbine engine when performing calculations

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9
Q

What are advantages to industrial gas turbines?

A
  • No limits in size and weigh, unlike aero-engines
  • Nearly zero exhaust speed
  • About 100k operating hours between overhauls
  • Compactness for a given power output
  • Low vibration
  • Reliable: low dynamic stresses
  • Low cost per kg at larger sizes
  • Low emissions, low installation costs, low-cost power generation
  • Automatically changes from primary to secondary fuel while still operating
  • Easy to transport and made mobile for certain applications
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10
Q

What are disadvantages to industrial gas turbines?

A
  • Lower thermal efficiency compared to diesel engines
  • Relatively poor dynamic performance
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11
Q

What is the principle of heat exchange cycle/recuperation?

A

High pressure air leaving the compresor is heated by transferring heat from the hot exhaust gases in a counterflow exchanger

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12
Q

What is the principle of the reheated cycle?

A
  • Splitting expansion over a HP and LP turbine
  • Reheating air between the HPT and the LPT to increase specific work
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13
Q

Where is the optimum reheating point in the flow?

A

When the pressure ratios of the HPT and the LPT are equal

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14
Q

How is the efficiency reduction in a reheated cycle overcome?

A

By adding a heat exchanger between the compressor and the combustor chamber.
- The hot exhaust gases are utilized in the heat exchanger
- The increase in work output is not offset by the increase in heat supply
- Efficiency is higher when the reheat is used together with a heat exchanger

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15
Q

What is the princple of the intercooled compression cycle?

A
  • Splitting compression into a LP and HP compressor
  • Intercooling the gas flow between the LPC and HPC
  • Cycle efficiency is only increased if a heat exchanger is employed at the same time as the intercooler
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16
Q

When is the maximum effect of intercooling achieved?

A

When the pressure ratios of the LPC and the HPC are equal

17
Q

What are disadvantages to intercooling?

A

Bulky and need large amount of cooling water

18
Q

What are the assumptions of the real gas turbine cycle?

A
  • Adiabatic flow (mechanical heat transfer magnitudes larger than heat transfer through wall)
  • Ideal gas as working fluid
  • Specific heat and specific heat ratio is dependent on and varies with temperature
  • Added and extracted mass flows must be considered
  • Efficiencies for compression and expansion are less than unity
  • Polytropic compression and expansion
  • Irreversible processes
  • Most processes are unsteady
19
Q

What is entropy and why is it caused?

A

A non-recoverable energy loss that occurs in all real cycles.
It is caused by molecular disorder in the fluid of the flow.

20
Q

What are the different categories of gas turbines?

A
  • Heavy-duty gas turbines
  • Aircraft-derivatives: originally aircraft engines adapted for electricity generation
  • Industrial-type gas turbines: extensively used in petro-chemical plants for compressor drive trains
  • Small gasturbines: usually centrifugal compressors and radial inflow turbines
  • Micro-turbines
21
Q

What is a free power turbine?

A

The engine has two turbines, one that drives the compressor and the free turbine that drives the load and is completely disconnected from the compressor

TMMV12 (10 decks)

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