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GATE 2019: Heat Transfer Quiz 3

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Question 1

In natural convection, relative velocity between plate and air is due to

Question 2

Forced convection is not governed by which of the following dimensionless parameters?

Question 3

A thermal conducting pipe having inner diameter 0.3m and outer diameter 0.305m having inside heat transfer coefficient 35 W/m2k and outside heat transfer coefficient as 25 W/m2k and having no fouling factor that accounts for surface dirt as well as consider that the thickness of pipe is so small that thermal conduction resistance through the is negligible. Calculate the overall heat transfer coefficient
(In W/m2k)

Question 4

A thermocouple, the junction of which can be approximated as 6mm diameter sphere is used to measure the temperature of a gas stream. The properties of the junction are c = 320 J/kg-K and k = 35 W/m-K. The heat transfer coefficient between the junction and gas is 210 W/m2-K. The time required for the thermocouple to read 90% of the initial temperature difference is ___________ s.

Question 5

An oven is maintained at a temperature of 625 the inner suface temperature is assumed to be 625 also the outer wall of the oven is exposed to ambient condition of temperature 25 having heat transfer coefficient of 250 W/m2k. the wall thickness is 30 mm and heat dissipation is 10^5 watt/m2. Thermal conductivity of the material is 1000 w/mk find the temperature of the outer surface of the oven wall

Question 6

Air flows at a heated plate at a velocity of 42m/s. The local skin friction coefficient of plate is 0.005. Estimate the local heat transfer coefficient(in W/m2k) at that point. The properties of air are as follows: ƿ= 0.89kg/, μ= 2.286×kgm/s, Cp= 1.001kJ/kgK, k= 0.04W/mK. Use St=.
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