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-   -   Heat Transer Help (http://www.cfd-online.com/Forums/floefd-floworks-flotherm/64263-heat-transer-help.html)

cag May 5, 2009 10:57

Heat Transer Help
 
I am attempting to model a very simple problem. An aluminum cylinder with a resistor inside. I want to know the steady state temp of the resitor, internal air, internal cylinder wall and external cylinder wall. I am running 4W through the resistor. Sounds easy but I am running into an issue.

Experimentally, I am getting temperature in the range of 10-15C above ambient for the cylinder walls. In FloWorks, I am getting temperatures ~ 200C above.

As my heat source, I selected a volume source of representative size and meterial properties and assigned a 4W heat source. Is this correct? If so, where could my problem be?

I run the tutorial with the fan in the computer box and get the correct answers. When I shut the fan off, I get very high temp values for that model as well?

Kwagga May 11, 2009 01:57

If I had to guess, I'd say the problem lies with the atmosphere around the outside of the cylinder. It's either not being modeled at all, or is too small.

I don't have enough experience to help you model a infinite volume of ambient air around the cylinder, so I'd suggest a very low airflow over the outside of the cylinder.

Edd May 11, 2009 08:54

I suspect that no heat is being dissipated at the outside of your cylinder. There should be some kind of convection: natural or forced.

There should be an additional air box around the subject for either type. You're probably interested in natural convection. Be sure to enable gravity. You should also define an air inlet and outlet (probably the surface below and above the subject). You can do this by assigning a "pressure potential" with environmental pressure to these surfaces.

good luck

bighead May 18, 2009 04:55

Hi, did your solution converge ? If yes, then I suggest you draw the thermal network to see where heat is going into and out of the system ... will be easier to troubleshoot on the model ... If no, then heat is probably stored inside the cylinders with no where to go, hence the high temp of 200C ... hence, you need to check your boundary conditions or ambients


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