Temperature drop over long length of tube
Temperature drop over long length of tube
(OP)
Hi, I need to calculate the end temp of natural gas sent over 585' in 1/2" bare SS316 tubing. Temp is initially 660F and a constant flow of 40scfh. How do I go about finding the final temp of natural gas from the end of the tube to determine if I need insulation/heat trace?
I read some resources on heat transfer rate using thermal conductivity of SS and air but nothing really directs me to finding the final temp.
I read some resources on heat transfer rate using thermal conductivity of SS and air but nothing really directs me to finding the final temp.
RE: Temperature drop over long length of tube
If you're worried about how cold it could get, then if it rains or snows outside, that will set your shellside (tube exterior) conditions for the heat transfer calc. For snow, set the tube exterior to a uniform temperature of 0 C...heat transfer will be controlled by the tubeside film coefficient entirely.
If it is indoors, you need only the ambient temperature and an estimate of the free convection heat transfer coefficient for the tubeside. Estimates good enough for what you're doing can be found in a table- you don't need to calculate it in detail using correlations. It then becomes a straightforward single tube heat exchanger calculation, a model for which you can find in any heat transfer textbook. The thermal conductivity of the tube metal is unlikely to matter, as both your tubeside and shellside convection film coefficients will be poor relative to the conductivity of a thin piece of just about any metal. But the model you find in a heat transfer text will take the metal into account, just in case. If your calculation shows that the tube metal is a significant fraction of the resistance, you've done something wrong.
RE: Temperature drop over long length of tube
For 15m of pipe (unless you meant 585 feet) it might be very low if your velocity is high.
How accurate do you have to be?
A pipe at 660F (350C) is a major safety hazard so I would imagine you need to insulate for personnel protection purposes regardless and really - how much does 15m of insulation for a 1/2" pipe cost??
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RE: Temperature drop over long length of tube
RE: Temperature drop over long length of tube
If you're actually trying to cool it then you're in a lot more difficulty, especially if this pipe is outside somewhere. you'll probably need to break the pipe into a lot of different sections as simple equations don't like big changes in temperature from one end to the other.
What's the gas velocity?
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Also: If you get a response it's polite to respond to it.
RE: Temperature drop over long length of tube
RE: Temperature drop over long length of tube
RE: Temperature drop over long length of tube
Your maths and units don't match....
If the gas is basically at atmospheric pressure and temperature then you're looking at about 100"/sec or 8 feet a second. I suppose at 600F you might be double that?
So your gas would take 73 seconds to transit the pipe section. Or at a high temperature say 40 seconds. It might loose less heat than you think.
But if you are at say 1barg or 2 barg then it all changes rather a lot.
Also if you're changing gas temp by several hundred degrees F then your gas density is going to change as well adding even more complication to your calculation.
But wind, rain, snow, if outside all has a big impact.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Temperature drop over long length of tube
RE: Temperature drop over long length of tube