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# GATE 2020: Heat Transfer Quiz 5

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Question 1

A solid sphere of radius r1 = 20 mm is placed concentrically inside a hollow sphere of radius r2 = 30 mm as shown in the figure.

The view factor F21 for radiation heat transfer is

Question 2

Two infinite parallel plates are placed at a certain distance apart. If the heat transfer between the plate is to be reduced by 80%, then the number of radiation shields required to be inserted between the plates is ___________.
[Assume that the emissivities of plates and radiation shield are equal]

Question 3

A domestic hot water tank (0.5 m diameter and 1 m high) is installed in a large space by the support of four small diameter  rod. The ambient temperature is 25°C. If the tank surface is oxidized copper with an emissivity of 0.8 and is at a peak temperature of 80°C, the heat loss from the tank by radiation is

Question 4

Two large parallel plates having a gap of 10 mm in between them are maintained at temperature T1= 1000 K and T2= 400 K. Given emissivity values, =0.5, =0.25 and Stefan-Boltzmann constant the heat transfer between the plates (in kW/m2) is ______

Question 5

Two very large parallel plane with emissivities 0.3 and 0.8 exchange radiative energy. The percentage reduction in radiative energy transfer when a polished aluminium radiation shield () is placed between them is __________%.

Question 6

A solid sphere 1 of radius ‘r’ is placed inside a hollow, closed hemispherical surface 2 of radius ‘4r’. The shape factor F2-1 is
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