Q.1. Two small parallel plane square surfaces, each measuring 4 mm × 4 mm are placed 0.
5 m apart (centre to
centre) with 300 angle between the radial distance and both the surface normals. The view factor between the
two surfaces is
Q.2. View factor of a large cylinder of 10 cm in radius and 60 cm in length from a coaxial smaller cylinder of
5 cm radius and the same length is 0.34. View factor of the larger cylinder of itself (concave inner surface) is
0.25. The view factor of the larger cylinder with respect to either annular end is.
Q.3. The conversion efficiency of a solar cell is 12%. For a maximum power output of 9 × 10 -3 W at an
incident solar radiation of 250 Wm-2, the required surface area of the solar cell in mm2 will be
Q.4. Two very large parallel walls (gray bodies) facing each other have emissivities of 0.5 and 0.7. The view
factor between these two walls is
Q.5. What is the value of view factor for two inclined planes having common edge of equal length and with an
angle of 20 degree
Q.6. Calculate the net heat transfer by radiation to a loaf of bread in an oven at a uniform temperature of 177
°C. The total surface area and temperature of loaf are 0.0645 m 2 and 100 °C respectively. The emissivity of
the surface of the loaf is 0.85.
Q.7. A continuous baking oven is used to bake cookies. The cookies move on a conveyor inside oven. The
temperature of top wall of the oven is 175 °C and surface temperature of cookie is 70 °C. The top wall of the
oven directly above the conveyor has an emissivity of 0.92 and the cookies have an emissivity of 0.8. The
layer of cookies on the conveyor is parallel to the top oven wall. Calculate the radiation factor.
Q.8. Two very large parallel plates are maintained at uniform temperature of 800 K and 500 K and have
emissivities of 0.2 and 0.7 respectively. Determine the net rate of radiation heat transfer between the two
surfaces per unit surface area of the plates.
Q.9. An 8 kW oven operating at 483 K is used to bake 150 loaves loaded in baking tins. The surface area of
each loaf is 0.024 m2. The temperature of loaf is 373 K. The emissivity of surface of loaf is 0.85. If only 85 %
of the heat is transmitted in the form of radiant energy, then calculate the energy use efficiency.
Q.10. Two very long Concentric cylinders of diameters 0.2 m and 0.5 m are maintained at uniform
temperatures of 950 K and 500 K and have emissivities 1 and 0.7 respectively. Determine the net rate of
radiation heat transfer between the two cylinders per unit length of the cylinders.
Q.11. Two concentric spheres of radii 0.15 m and 0.4 m are maintained at uniform temperatures 700 K and
400 K and have emissivities 0.5 and 0.7 respectively. Determine the net rate of radiation heat transfer between
the two spheres.
Q.12. The heating surface of an oven has an emissivity of 0.7 with 0.1 m 2 surface area and is maintained at
2800C. The view factor of this surface with respect to a piece of bread of 0.01 m 2 surface area is 0.05. If bread
has emissivity of 0.3 and receives 10 W of energy through radiation from the heating surface with Stephan –
Boltzman constant of 5.67 × 10-8 W m-2 K-4, the steady state bread surface temperature in 0C is
