I am not sure of the term Radiation Function, please help me understand.
Also, i have a doubt, say a hollow box is subjected to temperature of 100 DegC from the inside. and the outer surface is in contact with the air (ambient temp 20 DegC), what constraint should is define on the outer surface of the box. Radiation of Convection
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The basic equation for the heat emitted by a black body is SBC*T^4, where SBC is the Stefan-Boltzmann constant, and T is the absolute temperature. The "radiation fuction" that you enter into the software adjusts the equation to be (radiation fuction)*SBC*T^4. You use the "radiation function" to compensate for such things as emissivity, wavelength of the radiation, angle of incidence, view factors, and so forth.
If your example, ask yourself what happens in the real world? Is there convection? (Yes since it is in contact with the air.) Is there radiation? (Yes, unless you have something that blocks the radiation.) Is one of those forms of heat transfer negligible? Maybe, but I do not know for sure. I suggest that you run the model two or three times, once with radiation and convection, once with convection, and optionally once with radiation. This will show the importance of each type of heat transfer in your particular situation.
Simulation Mechanical user since Dec 1997