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BARC 2021 ME: Heat Transfer Nuclear Quiz 2

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Question 1

It is desired to increase the heat dissipation rate over the surface of an electronic device of spherical shape of 5 mm radius exposed to convection with h = 20 W/m²k by encasing it in a spherical sheath of conductivity 0.08 W/m-k. For maximum heat flow the diameter of the sheath will be

Question 2

The effect of forced convection can be neglected if

Question 3

A steel ball of 10 mm diameter at 1000 K is required to be cooled to 350 K by immersing it in a water environment at 300 K. The convective heat transfer coefficient is 1000 W/m²‐K. Thermal conductivity of steel is 40 W/m-K. The time constant for the cooling process 𝜏is 16 s. The time required (in s) to reach the final temperature is __________

Question 4

A hollow cylinder 10 cm internal diameter and 20 cm outer diameter has an inner surface and outer surface temperatures are 300

and 200

. The thermal conductivity of cylinder material is 80 W/m-k. The area of the cylinder per meter length such that cylinder can be transform into an equivalent slab is

Question 5

A triangular duct of unit length with surface temperature given in fig. length of side of triangle are L₁ =100 mm, L₂ = 120 mm, L₃ = 150 mm

Find the ratio of net radiant heat interchange from 1 – 2 surface to the 1 -3 surface.

Question 6

A plane wall of 0.2m thickness and 25 W/m-K thermal conductivity is uniformly generating heat within the slab. The slab is exposed to a fluid at 92^oC & the convection heat transfer coefficient between the wall and the fluid is 500 W/m²-K. If the uniform volumetric heat generation within the slab is 0.3 MW/m³, the maximum temperature in the wall is

Question 7

A cylindrical pin fin of diameter 5 cm and length 20 cm with negligible heat loss from the tip has an efficiency of 0.5. The effectiveness of this fin is _____.

Question 8

A motor cycle cylinder consist of ten fins, each 150 mm outside diameter and 75 mm inside diameter. The average fin temperature is 500 °C and surrounding air is at 20 °C temperature. The rate of heat dissipation is _______ W from the cylinder fins by convection, when motor cycle is stationery and convection coefficient h = 6 W/m²K.