Heat Transfer in Above Ground Gas Pipelines

[flowconsult]

I am trying to gauge the effect of not insulating a straight section of pipework upstream of an orifice meter. In particular I wish to determine the effect of ambient air on the flowing gas temperature. The pipeline is 24inch I/D with a 0.75inch wall thickness. Typical natural gas temperature is 8 oC to 15 oC, with an average flowrate of 265 Ksm3/h (194 t/h).

Any ideas would be most appreciated.

 

[quark]

Before doing any hard homework I would like to ask what exactly is needed. If your flow meter has temperature or pressure compensation then you need not worry about it. The error in compensated and non compensated measurement is more than 10% and is well established (by almost all the manufacturers) If at all you want to know how much heat flows into or out of NG, tell us ambient temperature and wind velocity.

 

[flowconsult]

THe metering station in question is a high accuracy custody transfer system with a total measurement uncertainty budget of 1.0%. It is normal practice to insulate the straight pipe sections u/s and d/s of the orifice fitting but on this installtion no lagging has been fitted. The main challange is to demonstate that the delta T between the ambient and gas temperatures will not significantly distort the temperature profile of the flowing gas. The ambient temperature varies between -4 oC and +25 oC.

Many thanks "quark" for your previous fast response.

 

[prex]

Just a rough check:
take C_p=2000 J/Kg°C for the gas, this makes about 100 kW the power that must be lost by the flowing gas to decrease its temperature of 1 °C.
Now take h=20 W/m²°C as the heat exchange coefficient to air and some [ignore]&Delta[/ignore];t=20 °C as the maximum temperature difference. One meter length of pipe, with outer surface area of nearly A=2 m² will lose hA[ignore]&Delta[/ignore];t=800 W. This means that 100 meters of uninsulated pipe would make a temperature change of only 1 °C: this seems to me quite negligible, but don't know what are your limits.
It is also to be noted that the effect of sunlight is not included in the above calculation, and, if present, wouldn't give a negligible effect. prex

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