Learning Forum

[António Oliveira]

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]

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

[António Oliveira]

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

[António Oliveira]

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]

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.