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# GATE 2023 || Heat Transfer || Quiz 50

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Question 1

For a non-black surface, absorptivity is 0.37 & reflectivity 0.29. Then the emissivity of the surface when the body is in thermal equilibrium with surrounding is

Question 2

The shields used between two surface is usually reduce the heat transfer by radiation between the two surfaces by

Question 3

Two infinitely large parallel plates 1 and 2 are held at temperatures 800 K and 500 K respectively and placed at a distance 50 mm apart in vaccum. A third large infinite flat radiation shield is introduced in between the plates 1 and 2. Consider emissivity of all the plates are equal. The ratio of the steady state radiative heat flux with and without the shield is

Question 4

Consider two infinitely long thin concentric tubes of circular cross section as shown in the figure. If D1 and D2 are the diameters of the inner and outer tubes respectively, then the view factor F22 is given by

Question 5

For Grey body, mono chromatic emissivity is _________.

Question 6

Calculate the total emissive power of a black body whose temperature is 573 ºC and Area is 5m2____.
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