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Measuring heat loss

  1. Jan 16, 2012 #1
    I am working on a problem where I am heating a hollow cylinder from the outside with a NiCr wire which is then insulated. The pipe is cooled by running water through the center of the hollow pipe. I would like to find the heat flux transfer rate outward.

    So my set up from the inside to the outside of the pipe is thermocouple 1, thermocouple 2, NiCr wire, insulation, thermocouple 3. Thermocouple 1 and 2 and inside the cylinder wall. Thermocouple 3 is on the outside surface of the insulation. Using temperatures from thermocouple 1 and 2, I can determine the heat transfer rate into the cylinder and then I can subtract that from the power input into the NiCr wire to determine heat transfer rate outwards. However I would like to verify this number using the temperature on the outside surface of the insulation. Is there a way to do this?

  2. jcsd
  3. Jan 17, 2012 #2
    Do you know the thermal properties of the insulation and its thickness?
  4. Jan 17, 2012 #3


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    Staff: Mentor

    The temperature on the outside surface of insulation is too close to ambient to be useful.
  5. Jan 17, 2012 #4


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    Homework Helper

    It is much easier to measure and model heat conduction through a solid (i.e. the metal pipe) than to model convective heat transfer accurately, especially for this type of situation where (if I understand it right) you have an insulated object, probably with a not very well defined geometrical shape, in free air.

    If you really want to measure it, I would be inclined to enclose the insulated pipe in a duct, blow air through it, and measure the temperature change and mass flow of the air. But it's probably not worth the bother.
  6. Jan 17, 2012 #5
    The the properties and thickness of the insulation is not particularly uniform and not known with any reasonable accuracy.

    You are the pipe and the heating wire surrounding the pipe are reasonably circular, however the insulation is not. You are correct and the insulated pipe is in free air. At the moment, everything outside the heat generating wire is exchangeable. Is there any way to measure the outward heat transfer if I were not constrained to the existing insulation and and outside temperature measurement?
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