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Determine inner wall temp of a pipe...

  1. Apr 3, 2016 #1
    I have derived a few equations to determine temp distribution through pipe wall in subsea conditions.

    However I am finding it difficult to determine what the wall temperature will be. I need to know and use this temperature to further my analysis.

    As of now I know the following parameters:

    -Fluid temperature within pipe = 66 degrees
    -Ambient temperature = 4 degrees
    -Wall thickness = 12.7mm
    -Inner radius = 0.1905

    Could you recommend a way I can determine the inner wall temperature? or point me in the right direction.

    Without this wall temp I am also unable to calculate heat flow rate or convection coefficients for inner and outer fluid.



    Many thanks
     
  2. jcsd
  3. Apr 3, 2016 #2
    You need to know the heat transfer coefficients inside and outside the pipe. Do you know how to estimate these?
     
  4. Apr 3, 2016 #3
    I have looked up many correlations, an example being nusselts number. but even in that correlation it required me to know the viscosity at wall, yet i still dont have the wall temperature, needed to calculate that.

    any other estimations i could try?
     
  5. Apr 4, 2016 #4
    The Nusselt number correlations are the way to go. Since you don't have the temperature at the wall, you will need to use trial and error. But, the term involving the viscosity at the wall is only a minor correction. You can start out using the average temperature of the fluid.

    chet
     
  6. Apr 4, 2016 #5
    ok, yes i was thinking of using an average temp. shall do. thanks
     
  7. Apr 4, 2016 #6
    Average temperature of what?
    You have an average temperature of the wall from entrance to exit.
    an average temperatue of the fluid from entrance to exit.
    an average temperature of the ambient fluid of convecton at entrance to exit.

    Which one will you choose?
     
  8. Apr 4, 2016 #7
    i was going for the second. average temp of fluid flowing in the pipe
     
  9. Apr 4, 2016 #8
    Could you somehow use the Seebeck effect to measure its temperature? I honestly have no idea how it would work, but I figured if you touch a different piece of metal to it and measure the voltage, you could do some math to convert it into a temperature.
     
  10. Apr 4, 2016 #9
    Since the viscosity of the fluid at the wall temperature is unknown, I am just wondering whether you can adopt the Dittus-Boelter equation/model to simplify the engineering estimations. The Dittus-Boelter equation is an explicit method for calculating the Nusselt number. It is easy to solve, and is an acceptable estimate for cases when there is a small temperature difference between bulk fluid and the pipe wall.
     
  11. Apr 6, 2016 #10
    Hi pocketengineer, thanks for the suggestion. However the Dittus Boelter model applies for turbuent flow, where as mine is laminar.

    I am doing for two cases water in pipe and methane in pipe, so i will be able to easily apply Dittus etc equation to the later.
    For the case with water in pipe (laminar flow) I will proceed with chestmillers suggestion in using the average fluid temp.

    Thanks
     
  12. Apr 6, 2016 #11
    If you want all the details on how to do it, see Transport Phenomena by Bird, Stewart, and Lightfoot.
     
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