Questions on Conjugate Heat Transfer+Radiation
Hello all,
I'm modeling a natural convection problem involving a heatsink and surrounding air. I want to look at the significance of radiation heat transfer due to different heatsink surface properties (polished, anodized, etc). But I have two questions on setting up a radiation heat transfer modeling in my case. (1) Do I have to turn on a radiation model or just to set wall boundary conditions to radiation? (I notice that the interfaces between the heatsink and surrounding air are twosided (coupled) walls and there is no radiation boundary option available) (2) If a radiation model is necessary, then which radiation model is appropriate to my problem? I would appreciate it if someone can help me out. Thank you in advance, Ken Adams 
Re: Questions on Conjugate Heat Transfer+Radiation
(1) turn on a radiation model

Re: Questions on Conjugate Heat Transfer+Radiation
Hi Ken,
The option to turn on radiation at the wall boundary condition refers to external radiation, i.e. heat is transfered from the surroundings to your heatsink via radiation. If u are interested in finding out how much heat comes into ur heat sink from the surroundings, u only need to set the wall radiation in the wall boundary conditions. There is no need to turn on any of the radiation models. However, since you are studying a heat sink, you would be interested on the radiation heat transfer from the heatsink to the atmosphere(radiation heat transfer goes from hotter surface to cooler surface). For this, you would need to turn on the radiation model. You would want to try the DO model, which is recommended for a localised heat source (which i presume would be your computer chip which emits heat to the heatsink) Basically for all radiation models, you would need to input 3 extra parameters in your materials panel. The scattering coefficient, absorptivity coefficent and refractive index. p.s: i am also modelling a heatsink..gd luck on finding the 3 coefficents as i cant seem to figure out how to calculate them cheers, Anthony 
Re: Questions on Conjugate Heat Transfer+Radiation
Hello Anthony,
Thank you for your clear explanations. Now I understand the whole picture. But I've got one more question: by using DO model, how do I specify the emissivity of heatsink surfaces? Thank you, Ken 
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