Heat transfer from Pipe to Pipe shoe support

[vester99]

I have a steel pipe that is insulated and held at a constant temperature of 750°F. Attached to it is a pipe shoe. The pipe shoe is a piece of structural steel WT4 x 20 welded to the pipe. The pipe shoe is sitting on a piece of Teflon. I would like to know how to calculate the approximate temperature at the bottom of the shoe that the piece of teflon will see. The ambient air temperature is 70°F.

      _
     /_    // \    \\_//  Pipe & Insulation
     \|/ 
    __|__   shoe(WT4 x 20)

I would appreciate it if someone could tell me what formulas to use and the order in which I should use them.

Thanks

HS

 

[pmover]

complete dimensional data of the pipe shoe is needed to solve the problem.

the method of heat transfer is conduction and convection.

that is: q = k x A x dt/dx (heat transfer via metal)
and
q = h x A x dt (heat transfer via air surrounding metal)

i trust that you are capable of or have access to someone whom can solve the problem.

i think you are questioning whether or not the teflon will deteriate. good question and worthy of investigation, especially that teflon is limited to about 450°F. (still thinking) i think that since the cross-sectional area is rather small, it may not be a problem - but still worthy of investigation.

again, detailed dimensional data on pipe shoe is needed.

-pmover

 

[JKEngineer]

I did a similar calculation as a demo when I was bidding a job about 2 years ago. My approach is to use FEA software and set the conditions as they are known. Then the solution "pops" out.

If you are still in the design stage, I'd be glad to do the same. If the system already exists, you could measure it with a thermocouple, contact thermometer, or IR system (which I also do).

In any event, any calculation, whether hand or FEA, will need materials info, dimension info, and environmental info (your 70F and air velocities if any). Also need to know what is on the back side of the teflon.

HTH Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[CHD01]

You've gotten good advice.

I think it will not be a problem either.

The conductive heat is limited by the heat flux at the minimum cross section of the pipe support; and the distance between pipe and teflon support. Yuor unknow is the temperature of the pipe support. Set this conductive heat transfer equation equal to the convective heat transfer equation and solve for temperature of metal suppport. I think you be able to check your result by also determining the total mass of metal for the support and then solving for the temperature increase of the metal due to the conductive heat transfer calculated earlier.

Refer to a good heat transfer text for the physical properties needed. I would assume a convective heat transfer coefficient between metal support an air of 2 BTU/Hr-ft2-Deg F. Conductivity for steel is 35 BTU/Hr-Deg F/Ft.

Good Luck! The more you learn, the less you are certain of.

 

[prex]

Really no need for FEA to approach this problem.
Let's take some reasonable assumptions, as you didn't specify everything:
-insulation is almost as thick as the Tee stem length, so the stem will only conduct heat with no exchange to the atmosphere
-upper surface of Tee flange is exposed to atmosphere and exchanges in a quiet ambient (no wind)
-lower surface of flange is fully in (good) contact with a piece of PTFE that is in turn in full contact with a well conducting material (metal). Note that the result will critically depend on thickness and conductivity of PTFE.
The equation for the unknown temperature of flange T_x is (meaning of symbols is evident if you know a little of thermal calcs):
k_st_w(T_p-T_x)/(d-k)=(k_P/t_P+h)b_f(T_x-T_a)
Taking:
k_s=60 W/m°C
t_w=9 mm (0.36 in)
T_p=400°C (750°F)
(d-k)=75 mm (3.06 in)
k_P=0.24 W/m°C (pure PTFE)
t_P=3 mm
h=10 W/m²°C (calm air)
b_f=205 mm (8.07 in)
T_a=20°C (70°F)
you should get (unless I'm in error)
T_x=127°C
With t_P=10 mm the result would be 213°C!
prex

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