Question

Question 29 LO3 (1 pt) Gas turbine engines require special metals and alloys for the various parts of the turbine which makes them more expensive. False True

Answer 1

Question 29:

Ans: Gas turbine is the part of a gas turbine engine from where work output is produced.

• The thermal efficiency of a gas turbine depends on the temperature of gas at the inlet of the turbine.
• In order for the turbine to withstand high gas temperatures, materials that suit the purpose have to be provided. This caused a demand for materials that can withstand higher temperatures without failure.
• The various types of alloys used to manufacture a turbine are Alloy 718 Nickel-based alloy, Alloy 706 Nickel-based alloy, Cr-Mo-V alloy, Cr alloys and A286 alloy.
• The cost per unit weight of these alloys are relatively large compared to ordinary materials.
• Therefore the answer is TRUE.

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Question 30:

Ans: Compressor is a device used to increase the pressure of a fluid. Compressor works by absorbing power from a prime mover.

• When air enters the compressor, mechanical work is done on the air to increase its pressure, ie., energy is added to the air. Hence the internal energy of the air increases.
• Since temperature is a function of internal energy, an increase in internal energy also causes an increase in its temperature.
• Also, compressors are usually insulated, ie., there is no loss of heat (energy) to the surroundings.
• Therefore the answer is TRUE.

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Question 31:

Ans: Simple Brayton Cycle is the idealised cycle for a Closed-cycle gas-turbine engines.

• The various processes involved in the Simple Brayton Cycle are:

1. Process (1-2): Isentropic compression (in a compressor)
2. Process (2-3): Constant-pressure heat addition (in a heat exchanger)
3. Process (3-4): Isentropic expansion (in a turbine)
4. Process (4-1): Constant-pressure heat rejection (in a heat exchanger)

Note: Isentropic process implies that a process is reversible as well as adiabatic.