**Question #1**

Consider the radiation heat exchange inside an annulus between two very long concentric cylinders. The radius of the outer cylinder is R_{o} and that of the inner cylinder is R_{i }. The radiation view factor of the outer cylinder onto itself is

(A) $\large 1-\sqrt{\frac{R_{i}}{R_{o}}}$

(B) $\large \sqrt{1-\frac{R_{i}}{R_{o}}}$

(C) $\large 1-\left ( \frac{R_{i}}{R_{o}} \right )^{1/3}$

(D) $\large 1-\frac{R_{i}}{R_{o}}$

**[GATE 16 S2, 1 mark]**

**Question #2**

Two large parallel plates having a gap of 10 mm in between them are maintained at temperatures T_{1} = 1000 K and T_{2} = 400 K. Given emissivity values, $\epsilon _{1}=0.5$ , $\epsilon _{2}=0.25$ and Stefan-Boltzmann constant $\sigma = 5.67\times 10^{-8} w/m^2K^4$ , the heat transfer between the plates (in kW/m^{2}) is ___________________

**[GATE 16 S3, 2 marks]**

**Question #3**

An infinitely long furnace of 0.5 m × 0. 4 m cross-section is shown in the figure below. Consider. all surfaces of the furnace to be black. The top and bottom walls are maintained at temperature T_{1} = T_{3} = 927 ^{o} C while the side walls are at temperature T_{2} = T_{4} = 527^{ o} C. The view factor, F_{1-2} is 0.26. The net radiation heat loss or gain on side 1 is_________ W/m. Stefan-Boltzmann constant = 5.67 × 10−8 W/m2-K4

**[GATE 16 S1, 2 marks]**

**Question #4**

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

(A) 1/12

(B) 1/2

(C) 2

(D) 12

**[GATE 15 S3, 2 marks]**

**Question #5**

The total emissive power of a surface is 500 W/m^{2} at a temperature T_{1} and 1200 W/m^{2} at a temperature T_{2}, where the temperatures are in Kelvin. Assuming the emissivity of the surface to be constant, the ratio of the temperatures T_{1}/T_{2} is

(A) 0.308

(B) 0.416

(C) 0.803

(D) 0.874

**[GATE 15 S2, 2 marks]**

**Question #6**

A hemispherical furnace of 1 m radius has the inner surface (emissivity, ε = 1) of its roof maintained at 800 K, while its floor (ε = 0.5 ) is kept at 600 K. Stefan-Boltzmann constant is 5.668 × 10−8 W/m2 .K4 . The net radiative heat transfer (in kW) from the roof to the floor is _______

**[GATE 14 S2, 2 marks]**

**Question #7**

A solid sphere of radius r_{1} = 20 mm is placed concentrically inside a hollow sphere of radius r_{2} = 30 mm as shown in the figure.

The view factor F_{21} for radiation heat transfer is

(A) 2/3

(B)4/9

(C)8/27

(D)9/4

**[GATE 14 S3, 2 marks]**

**Question #8**

Two infinite parallel plates are placed at a certain distance apart. An infinite radiation shield is inserted between the plates without touching any of them to reduce heat exchange between the plates. Assume that the emissivities of plates and radiation shield are equal. The ratio of the net heat exchange between the plates with and without the shield is

(A) 1/2 (B) 1/3 (C) 1/4 (D) 1/8

**[GATE 14 S4, 2 marks]**

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