# Power Plant Questions and Answers – Thermodynamics of Brayton-Rankine Combined Plant – I

This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Thermodynamics of Brayton-Rankine Combined Plant – I”.

1. If p and q are the efficiencies of a Brayton & Rankine cycles respectively in a Brayton-Rankine combined plant, the efficiency n of a combined plant is?
a) n = p/q
b) n = p+q-pq
c) n = pq
d) n = (1 – pq)

Explanation: The efficiency of a Brayton-Rankine combined plant when p and q are the efficiencies of a Brayton & Rankine cycles respectively is given as,
n = p + q – pq.

2. Which of these is a working fluid in the topping plant of a Brayton-Rankine combined plant?
a) Hydrogen
b) Helium
c) Nitrogen
d) All of the mentioned

Explanation: The low molecular mass of Helium makes it the most suitable working fluid in the topping plant.

3. Which of these is a working fluid in the bottoming plant of a Brayton-Rankine combined plant?
a) Mercury
b) Steam
c) Water
d) Air

Explanation: Water is the bottoming fluid due to its high specific heat capacity.

4. What would be the temperature of the gas in the combustion chamber?
a) 500 °C
b) 1600 °C
c) 1200 °C
d) 650 °C

Explanation: The gas in the combustion chamber is at a temperature of 1600 °C.

5. The efficiency of the open cycle gas plant is quite low. Why?
a) Gas gets cooled before reaching the turbine wheels
b) A lot of mechanical energy is used up by the compressor
c) Due to the presence of regenerator and absence of air pre heater
d) Both Gas gets cooled before reaching the turbine wheels and a lot of mechanical energy is used up by the compressor

Explanation: The efficiency of the open cycle gas plant is quite low. This is because of mainly two reasons,
Gas gets cooled before reaching the turbine wheels and a lot of mechanical energy is used up by the turbine wheels.
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6. To improve the efficiency of the gas turbines, which among these are used?
a) Regenerator
b) Inter cooling
c) Reheating
d) All of the mentioned

Explanation: All of the methods- Reheating, Regeneration and Intercooling are used to improve the efficiency of gas turbines.

7. What is regeneration?
a) Removal of heat from compressed air between stages of compression
b) Transfer of heat energy from exhaust gases to the compressed air flowing between compressor and the combustion chamber
c) To increase the temperature of partially expanded gases by burning more fuel
d) Transfer of heat energy from exhaust gases to the compressed air flowing between compressor and the combustion chamber and increases the temperature of partially expanded gases by burning more fuel

Explanation: Transfer of heat energy from exhaust gases to the compressed air flowing between compressor and the combustion chamber is called the process of Regeneration.

8. What is meant by inter cooling?
a) Removal of heat from compressed air between stages of compression
b) Transfer of heat energy from exhaust gases to the compressed air flowing between compressor and the combustion chamber
c) To increase the temperature of partially expanded gases by burning more fuel
d) None of the mentioned

Explanation: Removal of heat from compressed air between various stages of compression is called Inter cooling.

9. Which material is used for the manufacture of the turbine blades?
a) Stainless steel
b) Carbon steel
c) High nickel alloy
d) High alloy steel

Explanation: High nickel alloy is the most sufficient material for the manufacture of Turbine Blades.

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