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Thermodynamics HW Solutions 900

# Thermodynamics HW Solutions 900 - Chapter 11 Fundamentals...

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Chapter 11 Fundamentals of Thermal Radiation 11-79 The variation of emissivity of an opaque surface at a specified temperature with wavelength is given. The average emissivity of the surface and its emissive power are to be determined. Analysis The average emissivity of the surface can be determined from εε ε ε λλ λ λ () ( ( Tf f f f =− 12 3 1 1 +) + 2 ) λ 2 2 T where are blackbody radiation functions corresponding to . These functions are determined from Table 11-1 to be ff λ 1 and 1 T and λμ μ μ λ λ 1 2 2 0140256 6 0819217 T T =⎯ ⎯= (. m)(1200 K) = 2400 mK f m)(1200 K) = 7200 mK f 1 2 ε λ λ , μ m 2 6 0.85 0 and 0.577 = + + = ) 819217 . 0 1 )( 0 . 0 ( ) 140256 . 0 819217 . 0 )( 85 . 0 ( ) 140256 . 0 )( 0 . 0 ( ε Then the emissive flux of the surface becomes 2 W/m 67,853 = × = εσ = 4 4 2 8 4 K) 1200 )( K . W/m 10 67 . 5 )( 577 . 0 ( T E 11-80 The variation of transmissivity of glass with wavelength is given. The transmissivity of the glass for solar radiation and for light are to be determined. Analysis For solar radiation, T = 5800 K. The average transmissivity of the surface can be determined from τ
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