Problem with sweep meshing method for flow domain with heatsink.
 

I am trying to apply sweep mesh method to flow domain with heatsink shown in figure (only flow domain, heatsink itself is not important). Ansys Mesher does not recognize this domain as sweepable. I watched some geometry decomposition tutorials for complex parts. Do I have to divide the domain into many small domains?


https://imgur.com/a/Bg8ngWh
https://imgur.com/a/Bg8ngWh

Yes, you must divide it into parts which could be extruded. Then make a multibody part out of the assembly. In mesh, right click on mesh, then go to show >> sweepable bodies and it will show you which bodies are sweepable. In your current geometry, none are.
Multizone will try to perform a sweep like mesh without cutting it into many parts, but isn't as good, and does not give you as much control. If you want specific instructions and meshing for your geometry, PM me.

The only sweepable structures here are the pins. The profile of whatever being sweeped shall not change along the entire sweep. In practice a single face is repeated a number of times. You should devide your geometry so that the sweepable body looks the same in either end. It can be joined by enabling Share topology, or using interfaces.