# Thermodynamics Questions and Answers – Brayton Cycle-2

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Brayton Cycle-2”.

1. How can regeneration be used to improve the efficiency of Brayton cycle?
a) the energy of exhaust gas can be used to heat up the air which leaves the compressor
b) heat supplied from external source thus decreases
c) the amount of heat rejected also decreases
d) all of the mentioned

Explanation: This is how a regenerator can be used in Brayton cycle.

2. The temperature of air leaving turbine is less than that of air leaving compressor.
a) true
b) false

Explanation: The temperature of air leaving turbine is more than that of air leaving compressor.

3. In the regenerator,
a) temperature of air leaving the compressor is raised
b) temperature of air leaving the turbine is raised
c) both of the mentioned
d) none of the mentioned

Explanation: This is done by using the heat from the turbine exhaust.

4. Which of the following statement is true for a regenerator?
a) mean temperature of heat addition decreases
b) mean temperature of heat rejection decreases
c) both of the mentioned
d) none of the mentioned

Explanation: The mean temperature of heat addition increases by using a regenerator.

5. By using a regenerator,
a) efficiency increases, work output decreases
b) both efficiency and work output increases
c) efficiency increases, work output remains unchanged
d) efficiency remains same, work output increases

Explanation: This is because mean temperature of heat addition increases and mean temperature of heat rejection decreases by using regenerator.
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6. Which of the following is true about a regenerator?
a) it is costly
b) it is heavy and bulky
c) it causes pressure losses
d) all of the mentioned

Explanation: This loss in pressure decreases the cycle efficiency.

7. When we add a regenerator, cycle efficiency always increases.
a) true
b) false

Explanation: The addition of regenerator after a certain pressure ratio decreases the cycle efficiency as compared to Brayton cycle.

8. When the turbine efficiency and compressor efficiency decreases, the cycle efficiency ____
a) decreases
b) increases
c) remains same
d) none of the mentioned

Explanation: The Brayton cycle is very sensitive to the efficiency of the turbine and compressor.

9. The ____ the pressure ratio, the ____ will be efficiency.
a) less, more
b) less, less
c) more, more
d) more, less

Explanation: This comes from the Brayton cycle efficiency in terms of pressure ratio.

10. As the pressure ratio increases, the efficiency steadily ____
a) decreases
b) increases
c) remains constant
d) none of the mentioned

Explanation: As pressure ratio increases, the mean temperature of heat addition increases and the mean temperature of heat rejection decreases.

11. The maximum pressure ratio is given by
a) (Tmin/Tmax)^((ɣ-1)/ɣ)
b) (Tmin/Tmax)^(ɣ/(ɣ-1))
c) (Tmax/Tmin)^((ɣ-1)/ɣ)
d) (Tmax/Tmin)^(ɣ/(ɣ-1))

Explanation: Here Tmax is the maximum temperature and Tmin is the minimum temperature which is the temperature of surroundings.

12. The optimum value of pressure ratio at which work capacity becomes maximum is given by
a) (Tmin/Tmax)^((ɣ-1)/2ɣ)
b) (Tmax/Tmin)^(ɣ/2(ɣ-1))
c) (Tmax/Tmin)^(2(ɣ-1)/ɣ)
d) (Tmax/Tmin)^(2ɣ/(ɣ-1))

Explanation: This is the optimum value of pressure ratio.

13. The relation between maximum pressure ratio and optimum pressure ratio is given by
a) optimum pressure ratio = (maximum pressure ratio)/2
b) optimum pressure ratio = maximum pressure ratio
c) optimum pressure ratio = sqrt(maximum pressure ratio)
d) optimum pressure ratio = (maximum pressure ratio)^2

Explanation: This relation comes from the expressions of optimum pressure ratio and maximum pressure ratio.

14. Which of the following statement is true?
a) maximum work done = (specific heat at constant preferred)*(sqrt(Tmax) – sqrt(Tmin))^2
b) efficiency of cycle = 1- sqrt(Tmin/Tmax)
c) both of the mentioned
d) none of the mentioned

Explanation: These expressions come from the maximum pressure ratio.

15. The efficiency of Brayton cycle can be increased by using staged heat supply or by use of staged compression with intercooling.
a) true
b) false