class 33 - 11/29/2010 Real Surfaces Chapter 12 Sections...

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11/29/2010 1 Real Surfaces Chapter 12 Sections 12.4,5 Intensity–rate at which emission from dA 1 passes through dA n . The area of intensity component of dA 1 perpendicular to direction of radiation is dA 1 cos θ . λ ω θ d d dA dq I e cos ) , , ( 1 , Φ ∫∫ = = 0 2 0 2 / 0 , ) ( sin cos ) , , ( ) ( φ ππ d G G d d I G i = = 0 2 0 2 / 0 , ) ( sin cos ) , , ( ) ( d E E d d I E e + = = 2 0 2 / 0 , ) ( sin cos ) , , ( ) ( d J J d d I J r e 0
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11/29/2010 2 Irradiation–radiat ion incident from all areas for intercepting surface ∫∫ = 2 0 2 / 0 , sin cos ) , , ( ) ( φ θ λ ππ d d I G i = 0 ) ( d G G Radiosity– all the radiant energy leaving a surface (including reflection) + = 2 0 2 / 0 , sin cos ) , , ( ) ( d d I J r e = 0 ) ( d J J
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11/29/2010 3 Absorptivity • The spectral, directional absorptivity : • The spectral, hemispherical absorptivity : Assuming negligible temperature dependence, ) , , ( ) , , ( , . , , φ θ λ α i abs i I I ) ( G abs • The total, hemispherical absorptivity : ) ( , G G G abs Reflectivity Reflectivity of an Opaque Material • The spectral, directional reflectivity : Assuming negligible temperature dependence: • The spectral, hemispherical reflectivity : ) , , ( ) , , ( , . , , ρ i ref i I I ) ( , G ref • The total, hemispherical reflectivity : ) ( G G G ref Transmissivity Transmissivity • The spectral, hemispherical transmissivity : Assuming negligible temperature dependence, () tr G G τ , ) ( ) ( , G G tr • The total, hemispherical transmissivity : 1 1 λλλ ατ ρατ ++= +++ G G tr
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11/29/2010 4 Unless an opaque material is at a sufficiently high temperature to emit visible radiation, its color is determined by the spectral dependence of reflection and absorption in response to visible irradiation. The spectral, hemispherical absorptivity of an opaque surface is shown: What is the solar absorptivity? If this is gray surface at 340 K, what is its total, hemispherical emissivity?
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class 33 - 11/29/2010 Real Surfaces Chapter 12 Sections...

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