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-   -   radiation source or heat flux BC? (http://www.cfd-online.com/Forums/cfx/20629-radiation-source-heat-flux-bc.html)

pi September 9, 2004 12:25

radiation source or heat flux BC?
 
Hi all,

when I try to calculate the heat transfer from a hot surface to the air surrounding, should I set that surface with a radiation source or as a heat flux boundary? Is there any difference?

thanks in advance for your help

pi

test September 10, 2004 01:06

Re: radiation source or heat flux BC?
 
Hi, What is important is to know is to ascertain if the temperatures in the domain are high enough so that radiation becomes the main form of heat transfer.

If you are looking at natural convection problems, I suppose the temperature ranges will be small and you can just specify Fixed temperature boundary condition on the hot wall...

Hope this helps

Regards, test

pi September 10, 2004 05:51

Re: radiation source or heat flux BC?
 
Hi,

this is the situation. It is just a black surface with a inner resistive load which supplies 600 W/m2. The surface is about 313 K (not high but I donīt know it exactly), which means roughly 500 W/m2. Does it mean that the other 100 W/m2 are dissipated by convection?

How to know a priori the ratio between convection and radiation?

thanks

pi

test September 10, 2004 09:13

Re: radiation source or heat flux BC?
 
I Donot suppose that Radiation will be dominating at these temperature unless you have a special situation. I would suggest you neglect Radiation and specify Fixed temperature boundary condition on the wall (Which will be more stable than the Heat Flux wall boundary condition) and start your simulation.

Let me know know the details of the physics of the problem you are solving. Tell em what is exactly happening in the system which u are trying to model.

Regards, test

pi September 10, 2004 10:44

Re: radiation source or heat flux BC?
 
Well, it is just a test for an oven (or any other hot stuff) in a room and visualize the convection around it. The point is that while I know quite acurate the heat flux (because I know the actual power comsumption) I donīt know the temperature. In addition I think that small deviations from the real temperature in the temperature set will have a greater influence in the final room temperature. What is your oppinion?

regards

pi


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