# Mechanical Engineering MCQs – Basic Thermodynamic Cycles ( Power Plant Engineering ) MCQs

#### Mechanical Engineering MCQs – Basic Thermodynamic Cycles ( Power Plant Engineering ) MCQs

Latest Mechanical Engineering MCQs

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#### Mechanical Engineering MCQs – Basic Thermodynamic Cycles ( Power Plant Engineering ) MCQs

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# Energy Analysis of Combined Cycles and Choice of a Gas Turbine

1. The maximum work attainable as the system comes in equilibrium with surrounding is called?
a) Energy
b) Availability
c) Exergy
d) Entropy
Answer: c
Explanation: Exergy is defined as, “The maximum work attainable as the system comes in equilibrium with surrounding”.

2. More the exergy ___________ is the work obtained from the system.
a) more
b) less
c) equal
d) very less
Answer: a
Explanation: Exergy is defined as, “The maximum work attainable as the system comes in equilibrium with surrounding”. Naturally, more the exergy, more is the work obtained from the system.

3. Which of these is a measure of energy quality?
a) Entropy
b) Enthalpy
c) Exergy
d) none of the mentioned
Answer: c
Explanation: Exergy is also a measure of the quality of energy apart from the work obtained from the system.

4. Exergic __________ is a measure of the perfectness of a thermal system.
a) enthalpy
b) efficiency
c) strength
d) degree
Answer: b
Explanation: Exergy is also a measure of the quality of energy apart from the work obtained from the system. For this, exergic efficiency is a measure of the perfectness of a thermal system.

5. The values of dry solid fuel ratio are highest in?
a) Coke
b) Coal
c) Wood
d) Natural Gas
Answer: c
Explanation: The values of the ratio are 1.05 for coke, 1.05-1.10 for coal, 1.15-1.30 for wood & 1.04 for Natural Gas.

6. Choice of a gas turbine depends most on which of these factors?
a) Compression ratio
b) Cut-off ratio
c) Pressure ratio
d) none of the mentioned
Answer: c
Explanation: The working a Brayton cycle can be estimated most effectively by pressure ratio, so it becomes the most important factor.

7. Gas turbines with intercooling, regeneration & reheat are more suitable for combined cycles.
a) True
b) False
Answer: b
Explanation: Increasing the stages in a gas turbine with combined cycles will decrease its efficiency.

8. What is the optimum pressure ratio range for a gas turbine to obtain optimum efficiency?
a) 7-8.5
b) 10.5-12
c) 9.5-10
d) 10-20
Answer: b
Explanation: The optimum pressure ratio range for a gas turbine to obtain optimum efficiency is 10.5-12.

9. What is that temperature called to which the exhaust gases of a gas turbine are cooled?
a) Oxygen Dewpoint
b) Carbon dioxide Dewpoint
c) Nitrogen Dewpoint
d) Sulphuric Acid Dewpoint
Answer: d
Explanation: As the maximum temperature of cooling that can be reached has to be the dewpoint of one of these gases, so the dewpoint of Sulphuric Acid [Sulphur dioxide discharge] is chosen.

10. With an increase in the combined cycle pressure ratio, the efficiency of the bottoming cycle?
a) increases
b) decreases
c) remains same
d) none of the mentioned
Answer: b
Explanation: The efficiency of the bottoming cycle is inversely proportional to the combined cycle pressure ratio, so this relation.

# 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)
Answer: b
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
Answer: b
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
Answer: c
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
Answer: b
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
Answer: d
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.

Combustion Mechanism, Equipment And Rising Methods MCQs

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
Answer: d
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
Answer: b
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
Answer: a
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
Answer: c
Explanation: High nickel alloy is the most sufficient material for the manufacture of Turbine Blades.

# Thermodynamics of Brayton-Rankine Combined Plant – II

1. In the Brayton Rankine combined plant in series, the efficiency of the bottoming plant is?
a) a product of two efficiencies
b) a sum of two efficiencies
c) difference of two efficiencies
d) none of the mentioned
Answer: a
Explanation: In the Brayton Rankine combined plant in series, the efficiency of the bottoming plant is,
(no) = nb x n2.

2. What does HRSG stand for?
a) Heat Recovery Stem Generator
b) Heat Recovery Steam Generator
c) Heat Recuperating Steam Generator
d) Heat Regenerative Steam Generator
Answer: b
Explanation: HRSG stands for,
Heat Recovery Steam Generator.

3. Fuel is burnt partially in the Combustion Chamber & partially in the __________
a) HRCG
b) HRSC
c) HRSG
d) Compressor
Answer: c
Explanation: Fuel is burnt partially in the Combustion Chamber & partially in the Heat Recovery Steam Generator.

4. Supplementary firing in a Brayton-Rankine combined cycle is?
a) Good
b) Less effective
c) Very effective
d) None of the mentioned
Answer: b
Explanation: Supplementary firing in a Brayton-Rankine combined cycle is less effective as there is no appreciable increase in overall efficiency due to this combined cycle.

5. What is the effect of Supplementary Firing on exhaust gas temperature?
a) exhaust gas temperature increases
b) exhaust gas temperature decreases
c) exhaust gas temperature remains steady
d) none of the mentioned
Answer: a
Explanation: the effect of Supplementary Firing on exhaust gas temperature is that the exhaust gas temperature increases from 800 Degree Celsius – 900 Degree Celsius.

6. Maximum supplementary firing refers to __________
a) The maximum fuel that can be fired with the oxygen available in the gas turbine inlet
b) The maximum fuel that can be fired with the oxygen available in the gas turbine exhaust
c) The maximum fuel that cannot be fired with the oxygen available in the gas turbine inlet
d) None of the mentioned
Answer: b
Explanation: Maximum supplementary firing refers to the maximum fuel that can be fired with the oxygen available in the gas turbine exhaust.

7. It is advantageous to use a Combustion chamber plant with maximum supplementary firing than Combustion Chamber installations.
a) True
b) False
Answer: b
Explanation: As maximum supplementary firing is of no use when it comes to Combustion chamber installations hence, the above statement is false.

8. Which among these plants are most efficient?
a) Open cycle
b) Combined cycle
c) Closed cycle
d) Either Open or Closed cycle
Answer: b
Explanation: Combined cycle plants have most efficiency as the include two independent cycles working in relation to each other.

# Advantages of Combined Cycle Power Generation

1. The overall plant efficiencies in case of a combined cycle power generation is?
a) Low
b) High
c) Very low
d) Very high
Answer: b
Explanation: It is practically possible to attain efficiencies near to 50% in case of a combined cycle power generation.

2. The investment cost related to the combined power generation is?
a) high
b) low
c) very high
d) none of the mentioned
Answer: b
Explanation: The investment cost related to the combined power generation is. This is because only 2/3 of the total output is produced in the gas turbine.

3. What % is the investment cost in Conventional steam power plant more than those in the combined cycle plants?
a) 10
b) 20
c) 30
d) 40
Answer: c
Explanation: The investment cost in Conventional steam power plant is 30% more than those in the combined cycle plants.

4. The amount of water required as coolant for a combined cycle plant is?
a) very high
b) less
c) medium
d) none of the mentioned
Answer: b
Explanation: The amount of cooling water required is only 40-50% of the steam power plant requirement.

5. Combined cycle plants have _____________ operation flexibility.
a) high
b) low
c) equal
d) very low
Answer: a
Explanation: The ease of operation, i.e, the ease with which the plant can be started and stopped is the operation flexibility.

6. Installations in stages is possible in Combined Cycle Plants.
a) true
b) false
Answer: a
Explanation: Because the gas turbines go into operation much sooner than the steam plants, installations in stages is possible in Combined Cycle plants.

7. Which of these has the most simple operation?
a) combined cycle plant
b) steam plant
c) combined cycle & steam plant
d) none of the mentioned
Answer: a
Explanation: Combined cycle plant is more flexible than the steam plant and so it has the simplest operation.

8. Combustion in a Combined cycle plant has ______ environmental impact.
a) serious
b) little/no
c) toxic
d) none of the mentioned
Answer: b
Explanation: As most of the processes of a combined cycle plant are degradable, so combustion in a combined cycle plant has no impact on the environment.

9. Cogeneration of heat & electricity is possible in a Combined cycle plants.
a) True
b) False
Answer: a
Explanation: One of the major advantages of a combined cycle plants is the cogeneration of heat & electricity.

10. Efficiency of Natural gas fired Combined cycle plants is more than that of coal-fired plants.
a) true
b) false
Answer: a
Explanation: As the efficiency of a combined cycle plant is high in comparison to that of steam power plant, naturally, the statement mentioned becomes true.