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-   -   Emissivity’s dependence on thickness? (http://www.cfd-online.com/Forums/main/120135-emissivity-s-dependence-thickness.html)

Jerry Pham July 1, 2013 09:36

Emissivity’s dependence on thickness?
 
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Hello,

I'm completely new to CFD and would like to ask some entry-level questions:
In some flow simulation softwares they usually requires specifying emissivity for surfaces, such as in Solidworks Flow Simulation this might appear as:

http://www.cfd-online.com/Forums/att...emissivity.jpg
but there is a question on the exact definition for this: it ϵ thickness-dependent?
According to http://en.wikipedia.org/wiki/Emissivity:
Although it is common to discuss the "emissivity of a material" (such as the emissivity of highly polished silver), the emissivity of a material does in general depend on its thickness. The emissivities quoted for materials are for samples of infinite thickness (which, in practice, means samples which are optically thick) — thinner samples of material will have reduced emissivity.

Most emissivities found in handbooks and on websites of many infrared imaging and temperature sensor companies are the type discussed here, total emissivity. However, the distinction needs to be made that the wavelength-dependent or spectral emissivity is the more significant parameter to be used when one is seeking an emissivity correction for a temperature measurement device.
I wonder in doing the calculations, does Solidworks (and other more sophisticated software) make any adjustment according to the actual thickness of a surface?

Jerry


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