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Temperature rise due to thermal load?

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solar321

solar321

Mechanical
Joined
Feb 1, 2011
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I have aluminum and fiberglass enclosures approx this size 12.2"x10.2"x6.25" (WxHxD) respectively. These enclosures will be installed outside and the solar load on them will be 1120W/m2. Consider the ambient temperature to be +55 deg C. So can someone tell me how to calculate the additional rise in temperature just due to the solar load?
Thanks!
 
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emissivity? absorptivity? windspeed? internal heat load?

Given the additional information, you simply equate the incoming solar and internal heat load with the exiting radiated and convected heat. There will be a single surface temperature that satisfies the equality.

IF you do not have an HT text, you should get one; this one is free for downloading:
TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize
 
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Thanks 'IRstuff' and 'ione' for your inputs. Right now I am considering no internal heat load. What I want to know is if this equation still holds good - Q=A*K*(delta T)/L
where Q = Solar Load, A = area exposed to solar load, K = thermal conductivity of aluminum, delta T = temperature difference between ambient and inside of enclosure, L = thickness of aluminum enclosure
Basically I am saying that the solar load is a heat source inside the enclosure and now want to know the rise in ambient temperature due to it?
 
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You have to equal the heat transferred by radiaton (Stefan-Boltzman law) to the heat transferred by internal convection (from the inside of the box to the wall) + conduction through the box’s walls + external convection.
This method doesn’t offer a direct solution, you have to start with a guess temperature and iterate the procedure until it converges.
 
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Where I am coming from is Telcordia standard GR-487 specifies '+46 deg C as ambient temperature + solar load' for design of electronic enclosures. I am assuming solar load of 1120 W/m2 on the enclosure and want to know how much it translates to temperature as I want to specify the ambient temperature range of +46 deg C + temp (not solar load). Hope I am explaining what I am looking for?
 
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I understood that from the first post. However, you've been given the procedure a couple of different ways already, and you seem to be not forthcoming on data. The basic equation looks like:

solar_load*absorptiivity*area1 = area2*htc*(Tbox-Tair)+ area3*emissivility*Planck*(Tbox^4 - Tamb^4)

Tamb is the emissive temperature of the environment
Tair is the air temperature
Solve for Tbox, which can be done manually, or through a solver routine such as the one inside of Excel.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize
 
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I don't know any other data besides what I already mentioned. My questions are:
absorptivity of what? aluminum?
area 1 = ?
area 2 = ?
area 3 = ?
htc = ?
planck = ?
what's the difference between Tamb and Tair?
What's Tbox4?
Can you plug the numbers that I have already provided in your equation so I know what is what?
Thanks!
 
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No it's not for school!
Thanks!
 
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