Thermodynamics HW Solutions 883

Thermodynamics HW Solutions 883 - Chapter 11 Fundamentals...

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Chapter 11 Fundamentals of Thermal Radiation 11-45 The variations of emissivity of two surfaces are given. The average emissivity, absorptivity, and reflectivity of each surface are to be determined at the given temperature. Analysis For the first surface: λμ μ λ 1 3 0890029 1 T =⎯ ⎯= (. m)(3000 K) = 9000 mK f The average emissivity of this surface is 0.28 = + = ε + ε = ε λ λ ) 890029 . 0 1 )( 9 . 0 ( ) 890029 . 0 )( 2 . 0 ( ) 1 ( ) ( 1 1 2 1 f f T The absorptivity and reflectivity are determined from Kirchhoff’s law 0.72 0.28 = = α = ρ ⎯→ = ρ + α = α = ε 28 . 0 1 1 1 K) 3000 (at For the second surface: 1 3 0890029 1 T m)(3000 K) = 9000 mK f ε λ λ , μ m 3 0.8 0.2 0.1 0.9 The average emissivity of this surface is
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