Radiation-II

For an opaque plane surface irradiation, radiosity & emissive power are respectively 20, 12, 10 w/m^2. The emissivity of the surface is

• 0.2

• 0.4

• 0.6

• 0.8

The self view factors of two infinitely long blackbody concentric cylinders with a dimeter ratio of 3 for the inner and outer cylinder respectively are

• 0, 2/3

• 0, 1/3

• 1, 1/9

• 1, 1/3

A solid cylinder(surface 2) is located at the centre of a hollow sphere(surface 1). The diameter of the sphere is twice the diameter of the cylinder. Length of the cylinder is same as the diameter of the cylinder. Shape factor of surface 1 of itself (F11) is................

• 0.375

• 0.625

• 0.75

• 1

Surface resistance of a body having emissivity 0.4 & area 1m^2

• 0.4

• 0.667

• 3.5

• 1.5

A long semi circular duct is shown. shape factor F22 is

• 1.36

• 0.73

• 0.56

• 0.36

Heat transfer rate per unit area(W/m^2) between two large parallel grey surfaces(emissivity=0.9) maintained at 400K & 300K is ................

• around 700

• around 800

• around 900

• around 1000

Rdiation heat transfer rate per unit area is 1000W/m^2 between two large parallel grey surfaces(emissivity=0.5 each) . By coating one plate its emissivity reduced to 0.25. If the temperature remains unchanged new rate of heat exchange in W/m^2 is ...................

• 300

• 400

• 500

• 600

Two long parallel surfaces, each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of equal emissivity of both sides. the number of shields required is .....................

• 3

• 13

• 18

• 21