lec_29 - is emitted in all directions from a surface per...

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Lecture # 29 Radiation: everything emits radiation. The intermediate portion of em spectrum from 0.1 to 100 microns is pertinent to heat transfer. Two features complicate description of thermal radiation: spectral distribution and directionality. Intensity: rate at which radiant energy is emitted at wavelength λ in θ , φ direction per unit area of emitting surface normal to this direction per unit solid angle about this direction, and per unit wavelength interval d λ . Emissive power: rate at which radiation of wavelength
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Unformatted text preview: λ is emitted in all directions from a surface per unit d λ per unit surface area. Irradiation: radiation incident from all directions Radiosity: accounts for all radiant energy leaving a surface, reflected and emitted. Besides definitions, what’s really important is how to find q. So, if a small surface area (10-4 m 2 ) emits diffusely with total hemispherical emissive power of 5 X 10 4 W/m 2 to area of 5 X 10-4 m 2 , what is rate of emission intercepted by A 2 and the irradiation G 2 on A 2 ?...
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