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Impact Of Ambient Temperature And Solar Radiation To A Gas Stream


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#1 Jon K

Jon K

    Junior Member

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Posted 06 April 2023 - 09:00 AM

Guys,
I'm working on a heat transfer topic and got stucked. I hope you can give me some hints. I don't want to bother you with every single figure of the

calculation. Just need some help if I have the correct understanding or not.


Basis:
Gas is flowing (<20 m/s) through an uninsulated carbon steel pipeline with 20 °C. The ambient temperature is 45°C.
I would like to calculate how much the gas will heat up.

What I did is to calculate the heat transfer coefficient for inside (alpha,i) of the pipeline using Re, Nu, Pr. I know it is a iterative calculation since the outlet temperature has to be assumed at first.
The result was an alpha,i of < 40 W/m²K.
For my understanding the outside heat transfer coefficient (alpha,o) is the sum of alpha,convection and alpha,radiation. Correct?
Which temperature difference do I have to consider? I guess ambient temperature to (medium) fluid temperature? Or is it the wall temperature of the wall?
However I calculated a value of roughly 6-7 W/m²K for alpha,o

I neglected the contribution of the pipeline (thickness, material) to the overall heat transfer coefficient U for now.


So far the above mentioned procedure is ok?


This pipeline is in a region with high solar radiation. I have a value of 1000 W/m² for solar radition.
How to deal with this value? Simply (for worst case assumption) multiply with 1/2 of the pipeline outer surface? That's a huge heat input then.
Or is it ok to assume that some of this solar radiation is reflected by the pipeline and will not contribute to the heating of the gas? If so how
much reflection is reasonable here? I guess it depends on painting color.
Perhaps I understand the definition of the solar radition wrong and the value 1000 W/m² really represents the heat input into the system.


Btw, it is ok to use solar radiation PLUS radiation due to temperature difference of fluid and ambient temperature (as mentioned above)


Thanks for your input!

Jon
 






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