I got a geometry that is actually a cylinder,a stl file imported, I want to set 3 different inlets on the top plane of cylinder, so how to divide this plane into 3 regions in MFiX? Do I need to divide this plane with other software used to process geometry before I import it into MFIX?
Do you have an image of this? It has to be 3D to use .stl, first of all. Second, you can setup your regions to “capture” the .stl facets of your liking using coordinate criterias, but the quality of this would probably also depend on the tessalation of your surfaces. I would recommend to do some face splitting and preparation in your 3D software first, so that they’re more easily found.
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Just thinking here - if you are actually considering having 3 inlets on a flat end face of a cylinder, then I think the easiest way to acheive this would be to have each of these faces slightly extruded outwards from the actual surface, just to make them selectable in Mfix. I don’t think this will be nearly as easy if the same surfaces are flush with the cylinder surface. If this is an option at all.
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Hello,kjetilbmoe, I appreciate your replies. I’ve just divided this surface into only two regions by selecting stl facet using coordinate criterias. The picture posted here is the screenshot of the deviding result, its quality indeed looks not good but this is the only way I can nearly achieve the splitting. I also gave it a go to have each of these faces slightly extruded outwards from the actual surface,but it didn’t work, I still got the unsplitted surface, maybe the way I select these surfaces with background box is wrong. I’ve been stuck here for two days. 
(green one and red one in the picture posted here)
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So you want an outer and inner circular inlet region? Please post your setup file and stl also, if you have the chance. You might have to fiddle with the region selections, and make sure the normals are pointing inwards and so on.
As you can see from some of the tutorials, the stl usually should stretch outside the mesh boundaries, to ensure a good “cut”. You may use the automatic sizing button after the stl is imported, but should then reduce the mesh extents just a little to get these good cuts at the inlets at least. Walls should be well inside the mesh. When this seems ok, you can proceed to make the region selections.