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Temperature rise due to thermal load?

Temperature rise due to thermal load?

Temperature rise due to thermal load?

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?

RE: Temperature rise due to thermal load?

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: http://web.mit.edu/lienhard/www/ahtt.html


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RE: Temperature rise due to thermal load?

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?

RE: Temperature rise due to thermal load?

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.

RE: Temperature rise due to thermal load?

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?

RE: Temperature rise due to thermal load?

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.


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RE: Temperature rise due to thermal load?

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?

RE: Temperature rise due to thermal load?

No it's not for school!

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