5 replies to this topic

[smalawi]

Hi all,

I’m calculating the temperature rise in an LPG line from solar radiation. The line is about 30 km long and is exposed to direct sun radiation. I need to check how much the temperature rise is if the line is shut in and if the line is flowing (steady state).

I also need to check the case for insulated line with Aluminum clad, this is because if the temperature rise leads to a final temperature above the bubble point, then two phase will develop. Insulating the line will eliminate the need to raise the line pressure to keep it all liquid.

This kind of calculation is not normally covered by simulations software’s that I know off e.g. pipephase. so I have checked few sources and made up my own calculation sheet, its mostly based on the API’s RP 521 for bare tube case. For the insulation case, I simply ratio the metal emissivity between Al & Steel.

below is a summary of the methodology

at maximum temperature Q solar = Q convection + Q radiation

Q solar = 330 Btu/ft2 x Pipe Area x Length
Q Convection = A x Area ^ B x (T line - T ambient)^C (A,B & C are factors & depend on conditions/geometry..., T ambient is max ambient temperature)
Q radiation = e x Area x ( T line ^4 - T ambient ^4) (Temperature is absolute units)

from trail & error by changing T line value, the line temperature is higher than ambient because of solar radiation. for steady state, I just fix the Q solar, and add Q convention & Q radiation to the pipe heat content (metal & fluid) and increase the temperature as the heat builds up

Anybody encountered similar situation before ?
Any thoughts, resources you can share ?

Cheers,
sm

[kkala]

Not having dealt with similar calculations, it may be useful to note that maximum design temperature of bare pipe due to solar radiation is considered as 70 oC here, where max solar radiation is about 1 kW/m2/h (practically same as 330 Btu/fl2/h). So your calculations have to comply with it in the corresponding case.
See http://www.cheresour...h__1#entry42543

[ankur2061]

smalawi,

Some interesting discussion on heat gain in pipeline due to solar radiation is available at:

http://www.eng-tips....=50915&page=283

http://www.cheresour...-pipeline-temp/

http://www.eng-tips....=101927&page=86

http://www.214m.com/...0416/26789.html

Additionally the equation given on page 36 of the attached link when applied in reverse will provide the heat gain for your application:

http://www.energyman...LUID PIPING.pdf

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 22 September 2011 - 03:24 PM.

[sheiko]

Kostas,

I believe you meant 1 kW/m2 instead of 1 kW/m2/h.

Regards

[kkala]

sheiko, on 23 Sept 2011 - 12:15 PM, said:

Kostas, I believe you meant 1 kW/m2 instead of 1 kW/m2/h. Regards

Yes sheiko, thanks (absent mindedness error).

[smalawi]

thanks all for your help,

I will update my spreadsheet with the new info and do a sensitivity check. will try to post these back once I finished.

cheers,
sm