The rate of energy emission from unit surface area through unit s

SOLUTION

Explanation:

Intensity of radiation:

The radiation intensity for emitted radiation I_e(θ, ϕ) is defined as the rate at which radiation energy dQ̇_e is emitted in the (θ, ϕ) direction per unit area normal to this direction and per unit solid angle about this direction. 

\({I_e}\left( {\theta ,\phi } \right)\; = \;\frac{{d{{\dot Q}_e}}}{{dA\cos \theta .d\omega }}\; = \;\frac{{d{{\dot Q}_e}}}{{dA\cos \theta \sin \theta \;d\theta d\phi }}\;\left( {\frac{W}{{{m^2}}}.sr} \right)\)

Emissivity (ϵ):

The emissivity of a surface represents the ratio of the radiation emitted by the surface at a given temperature to the radiation emitted by a blackbody at the same temperature.

For black body surface, ϵ = 1.

Irradiation (G):

The radiation flux incident on a surface from all directions is called irradiation G.

Absorptivity, reflectivity and transmissivity:

The fraction of irradiation absorbed by the surface is called the absorptivity α, the fraction reflected by the surface is called the reflectivity ρ, and the fraction transmitted is called the transmissivity τ.

\(\alpha + \rho + \tau \; = \;1\)