Heat transfer in pipe?
Heat transfer in pipe?
(OP)
Please bear with me, I have a structural background. If we are heating one end of an 18"Ø schedule 160 pipe to 225°F is there an equation that states the length of pipe until the heat dissipates and the pipe is back at the ambient temperature of 70°F? I imagine along the length of pipe it'll fall quickly to ambient temperature, maybe 6in away it is 200°F, 1ft at 150°F, 2ft at 100°F. Is there an equation that approximates this behavior and tells the length needed to return to ambient?





RE: Heat transfer in pipe?
RE: Heat transfer in pipe?
RE: Heat transfer in pipe?
As said above, what you are describing is essentially a sort of heat exchanger and maybe the question would be best in the heat transfer and thermodynamics forum. However the heat transfer rate will be affected by what is happening internally in the pipe, any coatings or other influence on the outer part of the pipe and crucially what is the fluid which is taking the heat away? - air or water? What velocity is present? If "natural convection" does the heat go up and disappear or does it re-circulate?
Is the pipe confined?
Lots of questions which will significantly affect the outcome. It is quite difficult to see how this would work and as BI sas, the amount of heat loss along the pipe could be significant - will this affect the heat input available to maintain a fixed temperature?
If you figure these out or assume some values, then yes there are calculations and equations to allow you to create a temperature profile in steady state, but unless you've got a lot of air movement, your initial guess for a pipe that thick might be an order of magnitude out.
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RE: Heat transfer in pipe?
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RE: Heat transfer in pipe?
RE: Heat transfer in pipe?
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RE: Heat transfer in pipe?
θ/θ1=cosh[m(L-x)]/cosh(mL)
where θ = (Temp on pipe surface at position x) - bulk air temp; θ1 = (Temp on pipe at x=0) - bulk air temp - units in deg K
m = [h.b / (k.A)]^0.5, where h is the sum of convective and radiative heat transfer coeff, averaged out over the length of the pipe (w/m2/degK), b = external perimeter or circumference of this pipe in metres, k=thermal conductivity of the pipe metal, w/m/degK, A=cross sectional area of the pipe metal wall, m2
L = length of pipe where θ approaches zero, which theoretically is ∞
x = length of pipe in axial direction
Values for h can be found in Perry's Chem Engg Handbook, 7th edn., page 5-14, table 5-2.
Play around with trial and error values for L and see what values give reasonable approaches to this value.
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