Question

An iron sphere has a radius of 0.7 meters and its surface temperature is 400 K. It is surrounded by air whose temperature is 300 K. The emissivity of iron and air is 0.985. to. Find the heat flux that is emitted by radiation from the iron sphere. b. Find the net flow of heat from the iron sphere.

Answer 1

The Stefan-Boltzmann equation, which describes the rate of transfer of radiant energy, is as follows for an object in a vacuum :

where = heat flux, = emissivity (1 for black body), = Stefan's constant, = absolute temperature of the object

If the object is not in vaccum and surrounded with air of temperature is then,

The emissivity of iron and air is, = 0.985.

Stefan's constant, Wm-2K-4

absolute temperature of the sphere, = 400K

absolute temperature of the surrounded air, = 300K

The heat flux that is emitted by radiation from the iron sphere, = 5.585317405 5.585Wm-2

b. Radius of the sphere, r = 0.7m

Area of the sphere, A = 4r2

The net flow of the heat from the iron sphere,

Q = AJ = 4r2J = 4 X 0.72 X 5.585 = 34.3917125699298  34.39W