# Power Plant Questions and Answers – Energy Analysis of Combined Cycles and Choice of a Gas Turbine

This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “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

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

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

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

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

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

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

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

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

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

Explanation: The efficiency of the bottoming cycle is inversely proportional to the combined cycle pressure ratio, so this relation.

Sanfoundry Global Education & Learning Series – Power Plant Engineering.

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