Solved Question Paper for Foreman (Mechanical) in Ministry of Defence, Junior Scientific Officer (Mechanical) in Ministry of Defence, Assistant Executive Engineer (Mechanical), Additional Assistant Director (Safety) (Mechanical), Senior Scientific Assistant (Mechanical), Ministry of Defence & Junior Works Manager (Mechanical), Ministry of Defence conducted by UPSC

11. The dimensionless number relevant to transient heat conduction is

(a) Fourier number

(b) Reynolds number

(c) Prandtl number

(d) Stanton number

Answer: (a)

12. In a furnace the thickness of the refractory wall lining is 150 𝑚𝑚 and the average thermal conductivity of the refractory material is 0.05 𝑊/𝑚K. If the temperature difference between the inner and outer sides of the furnace is 150°𝐶, the heat loss per unit area to the surroundings will be:

Answer: (a)

13. A pipe carrying hot gases is insulated with a material having a thermal conductivity of 0.15 𝑊/𝑚K. The average local heat transfer coefficient by convection to the ambient air is 3 𝑊/𝑚2𝐾. The critical diameter of the pipe under these conditions is

(a) 100 𝑚𝑚

(b) 130 𝑚𝑚

(c) 160 𝑚𝑚

(d) 200 𝑚𝑚

Answer: (a)

14. In solving a lumped parameter problem, which one of the following pair of non-dimensional numbers is used?

(a) Grashoff number and Biot number

(b) Prandtl number and Nusselt number

(c) Biot number and Fourier number

(d) Fourier number and Reynolds number

Answer: (c)

15. In a heat exchanger, hot gasses enter with a temperature of 250°𝐶 and leave at 50°𝐶. On the other side, air enters at a temperature of 50°𝐶 and leaves at 90°𝐶. The effectiveness of the exchanger is to be quoted as:

(a) 0.15

(b) 0.20

(c) 0.25

(d) 0.30

Answer: (b)

16. Statement (I): Knocking and pre-ignition are the two words explaining the same phenomena.

Statement (II): Pre-ignition occurs only in petrol engines.

(a) Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)

(b)Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I)

(c) Statement (I) is true but Statement (II) is false

(d) Statement (I) is false but Statement (II) is true

Answer: (d)

17. An ideal refrigerator has a capacity of 6 tones, with a COP of 6. The capacity of the prime mover to run the machine should be at least

(a) 2.5 𝑘W

(b) 3.5 𝑘W

(c) 4.5 𝑘W

(d) 5.5 𝑘W

Answer: (b)

18. In a vapour compression system, superheating of the refrigerant decreases COP, the reason being:

1. Increase of work input to the compression

2. It does not depend on refrigeration effect

Which of the above statements is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (c)

19. A heat pump working on a reversed Carnot cycle has a COP of 5. If it works as a refrigerator and consumes 2 𝑘W power, the heat absorbed by the refrigerator will be

(a) 6 𝑘W

(b) 7 𝑘W

(c) 8 𝑘W

(d) 9 𝑘W

Answer: (c)

20. The conditioned air supplied to the room must have the capacity to take up

(a) Room sensible heat load only

(b) Room latent heat load only

(c) Both room sensible heat load and room latent heat load

(d) Neither room sensible heat load nor room latent heat load

Answer: (c)



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