Temperature increase of Steel Pipe from Solar Radiation

[blobslosak]

Hi guys,

Long time reader, first time poster and would appreciate some help please

I've been going round in circles on the best method to approach this problem with.

I have 1.8 diameter polished steel duct with largest length between expansion joints of 57m. I am trying to work out a worst case scenario for the expansion of the duct due to heat gain from solar radiation.

Is the best way to approach it as an energy balance which will reach steady state over time? Then it would essentially be radiative heat in - radiative heat out - convection heat out.
As it is a worst case I'm willing to ignore the cooling effects of the air inside the duct, unless it's not too much trouble to add it's cooling affect in to the balance.

Essentially, I am unsure of the correct equation/method to use to find the temperature increase of the pipe solely from solar radiation.

Thanks in advance,

Steve

 

[ione]

Give a read to this thread, it could be useful

http://www.eng-tips.com/viewthread.cfm?qid=260363

 

[hacksaw]

you can start with a flat plate to get the temperature rise, that will give you a worse case condition and refine it from there, otherwise you resort to rule of thumb estimates based on actual experience, or a complete thermal analysis.

is your duct insulated?

 

[IRstuff]

"Is the best way to approach it as an energy balance which will reach steady state over time? Then it would essentially be radiative heat in - radiative heat out - convection heat out.
As it is a worst case I'm willing to ignore the cooling effects of the air inside the duct, unless it's not too much trouble to add it's cooling affect in to the balance."

Is the pipe contents hot or cold? What are the contents' heat carrying capacity? These questions have a direct bearing on which direction the convection actually transports.

Where is this pipe located? This will have a direct bearing on the amount of solar load relative to air temperature.

How much mass is there in the pipe? This affects the amount of time required to get the pipe up to temperature. Note that maximum solar load per MIL-HDBK-310 only occurs for about 2 hours a day, and precedes the air temperature maximum by about 3 hours.

TTFN

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[25362]

J.P.Holman's HeatTransfer, McGraw-Hill, shows a worked out exercise that may be helpful.