7/23/2019 Total Emissive Por. and Ref, Emisi, Transi

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TOTAL EMISSIVE POR:def as the total amount o radiations emitted by abody per

unit area and time . it is expressed in W/m2 .the emissive power o a black body ,

according to Stean boltman is proportional to abslute temp to the ourth power

!b"   σ   #$ W/m2 "   σ  % #$ W , were σ  " boltman &'(S#%(#").*+.- W/m2 0 $

(ii) Monochromatic (spectral) emissive power (!1%3. 4t is oten necessary todetermine the spectral distribution o the energy radiated by a surace. %t any given

temperature the amount o radiation emitted per unit wavelength varies at di5erent

wavelengths. 6or this purpose the monochromntic ernissive power ! o the surace

is used. 4t is defned as 4 rate o energy radiated per unit area o the surace per unit

wavelength. #he 4ota7 emisaive power is given by,l !"   ∫0

 INF 

 E lam  dlam W/m2

Absorptivity is defined as the ratio between radiation absorbed and incident radiation.

Reflectivity is defined as the ratio of radiation reflected to the incident radiation.

Transmissivity is defined as the ratio of radiation transmitted to the incident radiation.