Considering Pipe Heat Capacity in Heat Transfer Calcs

[Potcarb]

I was doing a heat calculation for fluid going through a steel pipe using internal convection of the fluid, conductivity through the pipe, and external convection to surrounding air... then I started to wonder: why do we usually neglect the heat capacity of the pipe itself? I've never seen this accounted for in a thermal circuit, but maybe the conduction is enough?

 

[IRstuff]

Because the heat capacity is only relevant for transient analysis; once you reach operating temperature, conservation of energy says that gozinta = gozouta, so it has no bearing on steady state calculations.

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[goutam_freelance]

If you by chance mean 'Thermal conductivity' instead of 'Heat capacity' the answer is that the thermal conductivity of metals are very high and so the thermal resistance of pipe walls are usually neglected.

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[racookpe1978]

Transient conditions in a real world pipe last 15 seconds to 2 minutes to 15 minutes , and the steady-state conditions last years. More or less, since outside air temperatures or winds or ice coverings or rain or what ever change regularly.

 

[Potcarb]

Thanks to everyone for your responses. My situation is related to the initial transient point. We have a liquid we need to unload through a hose and pipe to one of our tanks. I'm trying to figure out if there's a chance it could freeze somewhere in the line. I've done the calculations with a steady state assumption, which gives a safe exit temperature of the liquid, but I'm concerned the initial heat exchange to the steel pipe may mess that up. There are some larger fittings in the line that may take in more heat.

Does anyone have any advice, or is there a good resource you'd recommend I look into?

 

[goutam_freelance]

If you are considering transients with cold pipe etc. you should consider heat capacity of pipe also. It can be done without much difficulty

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[Latexman]

If you’d give some specific facts of the operation, our “gut feeling” or experience or instincts may help. What’s the T of the load? What’s the FP? What’s the design ambient T? Insulated or not? Pipe d? Unloading rate?

Also, Google something like “moving water won’t freeze” and do some research.

If you are really worried about it, the line can be traced and insulated.

Good Luck,
Latexman