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Heat Flux – Boundary conditions

    • António Oliveira
      Subscriber

      Hi, 

      I'm having a problem simulating a water heating element. In this case, I have a flow-through water pipe, where a heat flux of 35 W/cm2 is applied to the outer surface, but when I enter this value and run the simulation, the heat flux is not constant, as you can see in the image. But if I apply a temperature, e.g. 250ºC, the problem is solved and the entire surface stays at that temperature. Since I'm simulating in a steady regime, shouldn't I have a constant heat flux along the tube? 
       
      Also, can anyone explain how shell conduction works and whether it's necessary or advisable to apply it in this case? 
       
      Thank you.
    • Rob
      Forum Moderator

      How is the lack of uniform temperature showing that the flux isn't uniform? 

      • António Oliveira
        Subscriber

        But since I have constant heat flux, shouldn´t the temperature be equal by all the external surface of the wall?

      • António Oliveira
        Subscriber

        Oh yes, it's different to apply 35W/cm2 at the beginning, when the water is at 5ºC, than when it is already at a higher temperature at the end of the tube... 

        Thank you.

    • Rob
      Forum Moderator

      No, if the solver has to push some Watts into the fluid which gets warmer as it passes along the tube then the heat source also has to get warmer. 

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