The variations of the spectral emissivity of two surfaces are as given: Surface 1: ɛ1=0.3 0 ≤ λ < 4 µm ɛ2=0.8 4 µm ≤ λ < ∞   Surface 2: ɛ1=0.9 0 ≤ λ < 4 µm ɛ2=0.2 4 µm ≤ λ < ∞   Draw the spectral emissivities of two surfaces. Determine the average emissivity of each surface at T=4000 K. Also, determine the average absorptivity and reflectivity of each surface for radiation coming from a source at 4000 K. Which surface is more suitable to serve as a solar absorber?

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter11: Heat Transfer By Radiation
Section: Chapter Questions
Problem 11.68P: 11.68 Two infinitely large, black, plane surfaces are 0.3 m apart, and the space between them is...
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The variations of the spectral emissivity of two surfaces are as given:

Surface 1:

ɛ1=0.3 0 ≤ λ < 4 µm

ɛ2=0.8 4 µm ≤ λ < ∞

 

Surface 2:

ɛ1=0.9 0 ≤ λ < 4 µm

ɛ2=0.2 4 µm ≤ λ < ∞

 

Draw the spectral emissivities of two surfaces. Determine the average emissivity of each surface at T=4000 K. Also, determine the average absorptivity and reflectivity of each surface for radiation coming from a source at 4000 K. Which surface is more suitable to serve as a solar absorber?

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