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Radiation through fictive walls

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Old   October 25, 2011, 07:08
Default Radiation through fictive walls
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I have a hot box that is placed outside (in air). I want to model radiation and natural convection on this box. The box is enclosed in a bigger box that is the air domain.
The boundaries on the bigger box I set to be walls with constant temperature equal the ambient temperature.
The air will now circulate around the hot box due to natural convection.

The problem is how radiation should be specified on the boundaries of the bigger box. I use the S2S model.
If I set the transmissivity to 1 the walls become transparent, as they are in reality. Then I can specify an environmental radiation temperature that provides the radiation from outside into my domain. I am not sure if this is correct, or if it is better to use emissivity=0.8, meaning that the air outside act as a grey body. The difference on the temperature of the hot box is huge (5-10%).

I don't use solar load. In the solar load tutorial they use transmissivity=0.98 to let the solar radiation in to the solar collector.
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