Chapter 11 Fundamentals of Thermal Radiation 11-46 The variation of emissivity of a surface with wavelength is given. The average emissivity and absorptivity of the surface are to be determined for two temperatures. Analysis(a) For T= 5800 K:λμμλ110 99534T=⎯→⎯=(5.m)(5800 K) = 29,000 mKfThe average emissivity of this surface is 0.203=−+=−+=)99534.01)(9.0()99534.0)(2.0()1()(1121εffT(b) For T= 300 K:110 013754T→(5.m)(300 K) = 1500 mKf0.5 0.2 ελλ, μm5 and 0.89=−+=−+=)013754.01)(9.0()013754.0)(2.0()1()(1121ffTThe absorptivities of this surface for radiation coming from sources at 5800 K and 300 K are, from Kirchhoff’s law, α==0.203(at 5800 K) 0.89(at 300 K) 11-47 The variation of absorptivity of a surface with wavelength is given. The average absorptivity, reflectivity, and emissivity of the surface are to be determined at given temperatures.
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.