Category: Thermodynamics Objective Questions

Thermodynamics Multiple Choice Questions on “Brayton Cycle-1”.

1. A gas turbine power plant uses
a) Otto cycle
b) Rankine cycle
c) Brayton cycle
d) Diesel cycle
Answer: c
Clarification: The Brayton cycle is the air standard cycle for gas turbine power plant.

2. The Brayton cycle consists of
a) two reversible isotherms and two reversible isobars
b) two reversible isochores and two reversible adiabatics
c) two reversible isotherms and two reversible isochores
d) two reversible isobars and two reversible adiabatics
Answer: d
Clarification: These are the processes of Brayton cycle.

3. Which of the following is true for the Brayton cycle?
a) first sir is compressed reversibly and adiabatically
b) heat is added reversibly at constant pressure
c) air expands in turbine reversibly and adiabatically
d) all of the mentioned
Answer: d
Clarification: These processes take place in the Brayton cycle.

4. The efficiency of Brayton cycle is given by (rk is the compression ratio)
a) 1/(rk)^(ɣ-1)
b) 1 – 1/(rk)^(ɣ)
c) 1 – 1/(rk)^(ɣ-1)
d) 1/(rk)^(ɣ)
Answer: c
Clarification: This is the expression for efficiency of Brayton cycle and rk=compression ratio.

5. The efficiency of Brayton cycle depends on
a) compression ratio
b) pressure ratio
c) either compression ratio or pressure ratio
d) both compression ratio and pressure ratio
Answer: c
Clarification: The reason being, compression ratio can be expressed in terms of pressure ratio.

6. For the same compression ratio, the efficiency of Brayton cycle is ____ the efficiency of Otto cycle.
a) less than
b) equal to
c) greater than
d) none of the mentioned
Answer: b
Clarification: The expressions for efficiency of Brayton cycle and Otto cycle are same.

7. Both Rankine cycle and Brayton cycle consists of two reversible isochores and two reversible adiabatics.
a) true
b) false
Answer: b
Clarification: Both Rankine cycle and Brayton cycle consists of two reversible isobars and two reversible adiabatics.

8. In Rankine cycle, working fluid ____ , in Brayton cycle working fluid ____
a) undergoes phase change, remains in gaseous phase
b) remains in gaseous phase, undergoes phase change
c) undergoes phase change, undergoes phase change
d) remains in gaseous phase, remains in gaseous phase
Answer: a
Clarification: This is a difference in Rankine cycle and Brayton cycle.

9. For Brayton cycle, average specific volume of air that compressor handles is ____ the same of gas in a gas turbine.
a) equal to
b) more than
c) less than
d) none of the mentioned
Answer: c
Clarification: This is because the gas temperature is much higher.

10. A steam power plant works on ____ and a gas turbine works on ____
a) both work on Rankine cycle
b) both work on Brayton cycle
c) Brayton cycle, Rankine cycle
d) Rankine cycle, Brayton cycle
Answer: d
Clarification: This is a difference in a steam power plant and a gas turbine.

11. Which of the following is more popular for electricity generation?
a) gas turbine
b) steam power plant
c) both of the mentioned
d) none of the mentioned
Answer: b
Clarification: Because in Rankine cycle, specific volume of water in pump is less than that of steam expanding in steam turbine.

12. For the same compression ratio and work capacity, Brayton cycle handles ____ range of volume and ____ range of pressure and temperature than does Otto cycle.
a) larger, smaller
b) smaller, larger
c) both are same
d) none of the mentioned
Answer: a
Clarification: This can be seen in the p-V diagram of Brayton cycle and Otto cycle.

13. Why is Otto cycle more suitable in reciprocating engine field?
a) reciprocating engine field cannot handle large volume of low pressure gas
b) the engine size increases
c) the friction losses become more
d) all of the mentioned
Answer: d
Clarification: This is the reason why Brayton cycle is not preferred in reciprocating engine field.

14. In turbine plants, Otto cycle is more suitable than Brayton cycle.
a) true
b) false
Answer: b
Clarification: In turbine plants, Brayton cycle is used instead of Otto cycle.

15. Which of the following statement is true?
a) an IC engine is exposed to highest temperature only for a short period
b) a gas turbine plant is always exposed to highest temperature used
c) in a gas turbine plant, maximum temperature used should be less than that used in IC engine
d) all of the mentioned
Answer: d
Clarification: This is the reason why in turbine plants, Brayton cycle is preferred.

Thermodynamics Multiple Choice Questions on “Multi-Stage Compression”.

1. For minimum work, the compression should be ____
a) adiabatic
b) isothermal
c) isochore
d) isobar
Answer: b
Clarification: This is the condition for minimum work.

2. The temperature after compression is given by
a) T2=(T1)(p2/p1)^(n/(n-1))
b) T2=(T1)(p2/p1)^((n+1)/n)
c) T2=(T1)(p2/p1)^((n-1)/n)
d) none of the mentioned
Answer: c
Clarification: Here T2 is the delivery temperature.

3. As the pressure ratio increases, delivery temperature ____
a) increases
b) decreases
c) remains constant
d) none of the mentioned
Answer: a
Clarification: This comes from the expression T2=(T1)(p2/p1)^((n-1)/n).

4. The volumetric efficiency ____ when carried out in stages.
a) decreases
b) increases
c) remains constant
d) none of the mentioned
Answer: b
Clarification: This is the reason why compression is carried out in stages.

5. The first stage of compression is done in ____ cylinder and next stage in ____ cylinder.
a) both in high pressure cylinder
b) both in low pressure cylinder
c) high pressure, low pressure
d) low pressure, high pressure
Answer: d
Clarification: This is how compression is carried out in two stages.

6. After passing through HP cylinder, the gas is passed to an intercooler.
a) true
b) false
Answer: b
Clarification: The gas is passed through an intercooler after it is compressed in LP cylinder.

7. In perfect intercooling, gas from intercooler has temperature equal to
a) inlet temperature
b) outlet temperature
c) intercooler temperature
d) all of the mentioned
Answer: a
Clarification: This is called complete or perfect intercooling when gas leaves the LP cylinder.

8. In perfect aftercooling, gas from intercooler has temperature equal to
a) inlet temperature
b) outlet temperature
c) intercooler temperature
d) all of the mentioned
Answer: b
Clarification: This is called complete or perfect aftercooling when gas leaves the HP cylinder.

9. The ideal intermediate pressure is given by
a) 2*p2/p1
b) sqrt(p2/p1)
c) (p1+p2)/2
d) sqrt(p1*p2)
Answer: d
Clarification: This is the ideal intermediate pressure for minimum work of compression.

10. The work required in HP compressor = work required in LP compressor.
a) true
b) false
Answer: a
Clarification: This happens when work of compression is minimum.

11. The intermediate pressure which produces minimum work also results in
a) equal discharge temperatures
b) equal work for two stages
c) equal pressure ratios in two stages
d) all of the mentioned
Answer: d
Clarification: These are the results when we consider minimum work of compression.

12. Which of the following is true for a multi-stage compression?
a) there is reduction in work required for each stroke
b) overall efficiency increases
c) cylinders can be adjusted according to size and strength
d) all of the mentioned
Answer: d
Clarification: These are few advantages of multi-stage compression.

13. Multi-cylinders give
a) less uniform torque
b) better mechanical balance
c) need large flywheel
d) all of the mentioned
Answer: b
Clarification: Multi-cylinders need smaller flywheel and give uniform torque.

14. In a multi-stage compression,
a) lubrication difficulties are reduced
b) explosion hazards are lessened
c) leakage losses are reduced
d) all of the mentioned
Answer: d
Clarification: These are advantages of multi-stage compression.