11-27&12-02-2024Surface Property Example

.pdf
School
University of Minnesota-Twin Cities**We aren't endorsed by this school
Course
ME 3333
Subject
Chemistry
Date
Dec 19, 2024
Pages
8
Uploaded by MajorCrabPerson1063
Recap: Blackbody Emission – 3 LawsFor a specific temperature, each point on the curve is described by Planck’s LawAs T increases,(1)the amount of energy emitted (area under the curve, the SB law) increases (2)peak of emission shiftstowards shorter wavelengths (higher frequencies, Wein’s displacement Law)1Band emission:
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-“Total” refers the property is averaged over the spectrum;-“Normal” refers to the direction of polar angle (theta) being zero degree.
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“Normal” refers to the direction of polar angle (theta) being zero degree. Spectral emissivity depends on both wavelength and temperature.Total emissivity depends on temperature.
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How Do You Measure Emissivity? 4Emissivity measurements are relative measurements wrt a blackbody
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ExampleA thin-plate solar panel on a spacecraft in the universe above the atmosphere. This panel is made of a material with a spectral property shown in the figure below. Find (1) what is the total emissivity, (2) what is the absorptivity; (3) To main the panel at T = 500 K, do you need to design a heating or cooling system with a specified power?
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Recap: Surface properties (ε, α, ρ, τ ) and rad. flux
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ExampleA thin-plate solar panel on a spacecraft in the universe above the atmosphere. This panel is made of a material with a spectral property shown in the figure below. Find (1) what is the total emissivity, (2) what is the absorptivity; (3) To main the panel at T = 500 K, do you need to design a heating or cooling system with how much power?
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