Learning Forum

[jstapchuck2]

Hello,

I had some questions regarding some of the Boundary Conditions.

1. For the Radiation condition, does the 'Geometry' you select mean that it is emitting radiation to either ambient or surface-to-surface? Or does the selected geometry means it is absorbing the incoming radiation from either ambient or surface-to-surface?
   1. Furthermore, does it automatically obtain or emit the radiation from all other surfaces if 'Surface to Surface' is selected, so I don't have to select other faces on my model?
2. Do all surfaces automatically have the initial temperature set if there's not a prescribed temperature?
3. Does the 'Enclosure Type' being 'Open' basically mean the heat can emit to ambient (i.e. the openness)? So 'Perfect' means that if it is inside an enclosure, you assume to heat will escape?
   1. Going off of this, my model is basically an open box with a heat source in the middle. With that in mind, I should keep this as open, correct?
4. Furthermore, the 'Enclosure' number mean that it is included in the view factor calculations, correct? So should this number always equal the number of faces selected, that way it is not treated as just one surface?

Thank you

[Chandra Sekaran]

If you select some faces and mark them as radiation to ambient then these will emit/absorb heat (view factor of 1.0) with a single ambient temperature. On the other hand if you specify "surface-to-surface" radiation then the selected faces with same enclosure ID will radiate between the faces of that enclsoure. If , for example you have a hollow cube then the 6 faces on the inside will form one enclosure and radiate to each other. The outside faces of the cube may radiate to ambient or other faces of other parts using surface-surface radiation.
Yes, this is specified in the initial temperature specification
'Open' means not all radiated heat from a face will reach the other faces of the enclosure i.e. the sum of the view factors to other faces is not 1.0. So the remaining heat will go to a node with a specified temperature. "Perfect" essentially scales the view factors so that the sum of each row of the view factor matrix is 1.0. It is an approximation to a fully closed cavity. If your model is an open box then leave it as OPEN and specify an ambient temperature
Radiation is quite expensive in terms of cpu as it is highly nonlinear. So you want to restrict it to faces that really are involved in radiation. The "enclosure number" is a arbitrary number. An enclosure (say enclosure #1) can have as many faces as you need. Multilple enclosures are allowed so that you can have model radiation between faces in different regions of your model. For example if you have 3 caviities then you can have 3 enclosures.

[jstapchuck2]

Thank you for your response.
In regards to question 1, how do you know what the enclosure ID is? Is that what the enclosure number is that you described in my 4th question?
And similarly, how do you know if everything is in the same enclosure? Just based on if they share the same enclosure number?
For my example of a heat source inside an open box, if I have the heat source set to radiate via Surface-to-Surface, would all the inner walls of the box automatically be included in the enclosure as long as they have the same enclosure number?