Mechanical Engineering Thermodynamics – Set 15

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Q1. High air-fuel ratio in gas turbines

(A) Increases power output
(B) Improves thermal efficiency
(C) Reduces exhaust temperature
(D) Do not damage turbine blades

Answer: (C) Reduces exhaust temperature

Q2. Which of the following gas has the highest calorific value?

(A) Coal gas
(B) Producer gas
(C) Mond gas
(D) Blast furnace gas

Answer:(A) Coal gas

Q3. The __ is obtained when carbonization of coal is carried out at 500° to 700° C.

(A) Soft coal
(B) Hard coal
(C) Pulverized coal
(D) Bituminous coal

Answer: (A) Soft coal

Q4. The gas turbine cycle with regenerator improves

(A) Thermal efficiency
(B) Work ratio
(C) Avoids pollution
(D) None of these

Answer: (A) Thermal efficiency

Q5. The isothermal and adiabatic processes are regarded as

(A) Reversible process
(B) Irreversible process
(C) Reversible or irreversible process
(D) None of these

Answer: (A) Reversible process

Q6. A path 1-2-3 is given. A system absorbs 100 kJ as heat and does 60 kJ of work while along the path 1-4-3, it does 20 kJ of work. The heat absorbed during the cycle 1-4-3 is

(A) -140 kJ
(B) -80 kJ
(C) -40 kJ
(D) +60 kJ

Answer: (D) +60 kJ

Q7. The amount of heat required to raise the temperature of __ water through one degree is called kilojoules.

(A) 1 g
(B) 10 g
(C) 100 g
(D) 1000 g

Answer: (D) 1000 g

Q8. One kg of hydrogen requires 8 kg of oxygen and produces

(A) 1 kg of water
(B) 7 kg of water
(C) 8 kg of water
(D) 9 kg of water

Answer: (D) 9 kg of water

Q9. The absolute zero pressure can be attained at a temperature of

(A) 0°C
(B) 273°C
(C) 273 K
(D) None of these

Answer: (D) None of these

Q10. The efficiency of the Carnot cycle may be increased by

(A) Increasing the highest temperature
(B) Decreasing the highest temperature
(C) Increasing the lowest temperature
(D) Keeping the lowest temperature constant

Answer: (A) Increasing the highest temperature

Q11. The distillation carried out in such a way that the liquid with the lowest boiling point is first evaporated and re-condensed, then the liquid with the next higher boiling point is then evaporated and re-condensed, and so on until all the available liquid fuels are separately recovered in the sequence of their boiling points. Such a process is called

(A) Cracking
(B) Carbonization
(C) Fractional distillation
(D) Full distillation

Answer: (C) Fractional distillation

Q12. Otto cycle efficiency is higher than Diesel cycle efficiency for the same compression ratio and heat input because in Otto cycle

(A) Combustion is at constant volume
(B) Expansion and compression are isentropic
(C) Maximum temperature is higher
(D) Heat rejection is lower

Answer:(D) Heat rejection is lower

Q13. In an ideal gas turbine plant, it is assumed that the compression and expansion processes are

(A) Isothermal
(B) Isentropic
(C) Polytropic
(D) None of these

Answer: (B) Isentropic

Q14. The root mean square velocity of the gas molecules is given by (where k = Boltzmann’s constant, T = Absolute temperature, and m = Mass of one molecule of a gas)

(A) √(KT/m)
(B) √(2KT/m)
(C) √(3KT/m)
(D) √(5KT/m)

Answer: (C) √(3KT/m)

Q15. An open cycle gas turbine works on

(A) Carnot cycle
(B) Otto cycle
(C) Joule’s cycle
(D) Stirling cycle

Answer: (C) Joule’s cycle

Q16. The ratio of root mean square velocity to average velocity of gas molecules at a particular temperature is

(A) 0.086
(B) 1.086
(C) 1.086
(D) 4.086

Answer: (B) 1.086

Q17. One reversible heat engine operates between 1600 K and T2 K and another reversible heat engine operates between T2 K and 400 K. If both the engines have the same heat input and output, then temperature T2 is equal to

(A) 800 K
(B) 1000 K
(C) 1200 K
(D) 1400 K

Answer: (A) 800 K

Q18. A molecule consisting of one atom is known as

(A) Mono-atomic
(B) Di-atomic
(C) Tri-atomic
(D) Poly-atomic

Answer: (A) Mono-atomic

Q19. Which of the following process can be made reversible with the help of a regenerator?

(A) Constant pressure process
(B) Constant volume process
(C) Constant pvn process
(D) All of these

Answer:(D) All of these

Q20. For the constant pressure and heat input, the air standard efficiency of gas power cycle is in the order

(A) Dual cycle, Diesel cycle, Otto cycle
(B) Otto cycle, Diesel cycle, Dual cycle
(C) Dual cycle, Otto cycle, Diesel cycle
(D) Diesel cycle, Otto cycle, Dual cycle

Answer: (A) Dual cycle, Diesel cycle, Otto cycle

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