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# GATE ME 2022: Heat Transfer-9

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Question 1

Thermal diffusivity is _________.

Question 2

Critical radius of insulation for a wire of radius r is ____.

(k and h denote the usual parameters)

(k and h denote the usual parameters)

Question 3

In regarding nucleate boiling __________.

Question 4

Determine radiation heat loss from a steel tube of outside diameter 60 mm and 5m long at a temperature of 327 °C if the tube is inside a square conduit made of brick having 0.4 m side as shown in given figure and temperature of 25 °C. (Take, ε(steel)= 0.8, ε(brick)= 0.9.

Question 5

12mm diameter Steel balls are annealed by heating to 1150 K and then slowly cooling to 400K in an air environment for which T

_{∞}= 325 K and h=20 W/m^{2}K. If the properties of the steel are k = 40 W/m K, ρ= 7800 kg/m^{3}and c_{p}= 600 J/kg-K, what will be the time required for the cooling process?Question 6

A 1 cm diameter, 30 cm long fin made of aluminum (k = 237 W/m

^{o}C) is attached to a surface at 80^{o}C. The surface is exposed to ambient air at 22^{o}C with heat transfer coefficient of 11 W/m^{2 °}C. If the fin can be assumed as infinitely long, its efficiency is ___________.- 407 attempts
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Jul 8ESE & GATE ME

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