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## Simulation CFD

Member
Posts: 4
Registered: ‎11-28-2012

# Solar Reflectance

254 Views, 4 Replies
01-02-2013 04:40 AM

I am running a model with the Solar Heating feature and analyzing surface temperature on a peice of equipment.  I want to run sensitivty analysis on the color/coating used for the equipment but there doesn't seem to be a way to modify the solar reflactance of the object (either through material properties of boundry conditions).  Many of the coating options we are considering have very similar emissivity values, but significantly different reflectance properties.

Is there a way to assess/input solar reflectance with Autodesk Simulation CFD?

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Product Support
Posts: 723
Registered: ‎08-25-2011

# Re: Solar Reflectance

01-08-2013 12:40 AM in reply to: mwjansen

The only way here is through emissivity/transmissivity and reflectivity (which is not shown but is used in the calc).

The 3 must sum to 1 so if you reduce either the emissivity or transmissivity, the relfectivity will increase accordingly.

Jon Wilde
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Member
Posts: 4
Registered: ‎11-28-2012

# Re: Solar Reflectance

01-08-2013 04:02 AM in reply to: wildej

Thank you for your reply Jon.

I understand the simplified equation you mention: emissivity + reflectivity + transmissivity = 1. However, the coatings I am analyzing all have a similar emissivity but widely varying reflectivity. Since there doesn't seem to be a way too specifically manipulate reflectivity I have instead reduced the incident radiation in the flag manager. So the new solar intensity value = (1-reflectence) * Maximum solar intensity. Unfortunately this also reduces the incoming heat levels to other components of the scenario, which would normally emit at high levels.

I think this radiation detail may be beyond the functionality of CFD, however, I think i have gotten close enough with the surface temperature to accurately assess the natural convection component.

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Product Support
Posts: 554
Registered: ‎08-24-2011

# Re: Solar Reflectance

01-09-2013 06:48 AM in reply to: mwjansen

I think your true needs would be spectral radiation which we do not do.  Good to hear you have gotten close enough to your expectations.

-Royce

Royce Abel
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Member
Posts: 7
Registered: ‎10-05-2012

# Re: Solar Reflectance

04-10-2013 03:01 PM in reply to: mwjansen

I have run into this same situation, and the idea you propose seems like a logical work-around (especially if you know the solar absorptivity of the material).  The only thing I might suggest/add would be to modify your modified solar flux by dividing by your material emissivity (i.e., abosrptivity * initial flux = modified flux / emissivity = slightly higher modified flux).  I think this would be more correct since the gray model exchanges e and a equivalent and so your flux would be slightly reduced by your material emissivity.  Probably doesn't make significant difference, but thought I'd throw that out there.  Not sure what you do if you have shiny parts and painted parts exposed to solar in the same model though (other than just treat it as a surface heat flux).

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