# 439 Thermodynamic MCQ For All Mechanical Exams

351)The efficiency of Brayton cycle is given by (rk is the compression ratio)

1. a) 1/(rk)^(ɣ-1)
2. b) 1 – 1/(rk)^(ɣ)
3. c) 1 – 1/(rk)^(ɣ-1)
4. d) 1/(rk)^(ɣ)

Ans-C

352)The efficiency of Brayton cycle depends on

1. a) compression ratio
2. b) pressure ratio
3. c) either compression ratio or pressure ratio
4. d) both compression ratio and pressure ratio

Ans-C

353)For the same compression ratio, the efficiency of Brayton cycle is ____ the efficiency of Otto cycle.

1. a) less than
2. b) equal to
3. c) greater than
4. d) none of the mentioned

Ans-B

354)Both Rankine cycle and Brayton cycle consists of two reversible isochores and two reversible adiabatics.

1. a) true
2. b) false

Ans-B

355)In Rankine cycle, working fluid ____ , in Brayton cycle working fluid ____

1. a) undergoes phase change, remains in gaseous phase
2. b) remains in gaseous phase, undergoes phase change
3. c) undergoes phase change, undergoes phase change
4. d) remains in gaseous phase, remains in gaseous phase

Ans-A

356)For Brayton cycle, average specific volume of air that compressor handles is ____ the same of gas in a gas turbine.

1. a) equal to
2. b) more than
3. c) less than
4. d) none of the mentioned

Ans-C

355)A steam power plant works on ____ and a gas turbine works on ____

1. a) both work on Rankine cycle
2. b) both work on Brayton cycle
3. c) Brayton cycle, Rankine cycle
4. d) Rankine cycle, Brayton cycle

Ans-D

356)For the same compression ratio and work capacity, Brayton cycle handles ____ range of volume and ____ range of pressure and temperature than does Otto cycle.

1. a) larger, smaller
2. b) smaller, larger
3. c) both are same
4. d) none of the mentioned

Ans-A

357)Why is Otto cycle more suitable in reciprocating engine field?

1. a) reciprocating engine field cannot handle large volume of low pressure gas
2. b) the engine size increases
3. c) the friction losses become more
4. d) all of the mentioned

Ans-D

358)In turbine plants, Otto cycle is more suitable than Brayton cycle.

1. a) true
2. b) false

Ans-B

359)Which of the following statement is true?

1. a) an IC engine is exposed to highest temperature only for a short period
2. b) a gas turbine plant is always exposed to highest temperature used
3. c) in a gas turbine plant, maximum temperature used should be less than that used in IC engine
4. d) all of the mentioned

Ans-D

360)How can regeneration be used to improve the efficiency of Brayton cycle?

1. a) the energy of exhaust gas can be used to heat up the air which leaves the compressor
2. b) heat supplied from external source thus decreases
3. c) the amount of heat rejected also decreases
4. d) all of the mentioned

Ans-D

361)The temperature of air leaving turbine is less than that of air leaving compressor.

1. a) true
2. b) false

Ans-B

362)In the regenerator,

1. a) temperature of air leaving the compressor is raised
2. b) temperature of air leaving the turbine is raised
3. c) both of the mentioned
4. d) none of the mentioned

Ans-A

363)Which of the following statement is true for a regenerator?

1. a) mean temperature of heat addition decreases
2. b) mean temperature of heat rejection decreases
3. c) both of the mentioned
4. d) none of the mentioned

Ans-B

364)By using a regenerator,

1. a) efficiency increases, work output decreases
2. b) both efficiency and work output increases
3. c) efficiency increases, work output remains unchanged
4. d) efficiency remains same, work output increases

Ans-C

364)Which of the following is true about a regenerator?

1. a) it is costly
2. b) it is heavy and bulky
3. c) it causes pressure losses
4. d) all of the mentioned

Ans-D

365)When we add a regenerator, cycle efficiency always increases.

1. a) true
2. b) false

Ans-B

366)When the turbine efficiency and compressor efficiency decreases, the cycle efficiency ____

1. a) decreases
2. b) increases
3. c) remains same
4. d) none of the mentioned

Ans-A

367)The maximum pressure ratio is given by

1. a) (Tmin/Tmax)^((ɣ-1)/ɣ)
2. b) (Tmin/Tmax)^(ɣ/(ɣ-1))
3. c) (Tmax/Tmin)^((ɣ-1)/ɣ)
4. d) (Tmax/Tmin)^(ɣ/(ɣ-1))

Ans-D

368)The optimum value of pressure ratio at which work capacity becomes maximum is given by

1. a) (Tmin/Tmax)^((ɣ-1)/2ɣ)
2. b) (Tmax/Tmin)^(ɣ/2(ɣ-1))
3. c) (Tmax/Tmin)^(2(ɣ-1)/ɣ)
4. d) (Tmax/Tmin)^(2ɣ/(ɣ-1))

Ans-B

369)Which of the following statement is true?

1. a) maximum work done = (specific heat at constant preferred)*(sqrt(Tmax) – sqrt(Tmin))^2
2. b) efficiency of cycle = 1- sqrt(Tmin/Tmax)
3. c) both of the mentioned
4. d) none of the mentioned

Ans-C

370)The efficiency of Brayton cycle can be increased by using staged heat supply or by use of staged compression with intercooling.

1. a) true
2. b) false

Ans-A

371)The propulsive efficiency is given by

1. a) work done by engine / propulsive power
2. b) propulsive power / work done by engine
3. c) energy input rate / propulsive power
4. d) propulsive power / energy input rate

Ans-D

372)In aircraft propulsion the most widely used engine is

1. a) turbojet
2. b) turbofan
3. c) turboprop
4. d) all of the mentioned

Ans-C

373)The bypass ratio is the ratio of

1. a) mass flow rates of two streams
2. b) pressure ratio of inlet and exit
3. c) volume flow rate of inlet and exit
4. d) none of the mentioned

Ans-A

374)Dry ice is suitable for ____ temperature refrigeration.

1. a) high
2. b) low
3. c) all range of
4. d) none of the mentioned

Ans-B

374)A reversed heat engine

1. a) receives heat from a low temperature region
2. b) gives heat to a high temperature region
3. c) receives a net inflow of work
4. d) all of the mentioned

Ans-D

375)For a heat pump, coefficient of performance is given by (Q1 is the heat taken from low temperature region and Q2 is the heat given to high temperature region)

1. a) Q1/(Q1-Q2)
2. b) Q2/(Q1-Q2)
3. c) 1- (Q1/Q2)
4. d) 1- (Q2/Q1)

Ans-A

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