Expanding Air

TBE_Legend

http://www.comsol.com/community/forums/general/thread/587/

August 27, 2009 5:43pm HKT
Expanding Air
Hello,

I'm new to COMSOL and I'm trying to make a model of tube filled with air. The tube is heated. The problem is with the air. I found thermal expansion only in the solid, stress-strain module so I tried with it. But there are no elastic properties of the air in the library. Should I use other module and if yes what, or I can make it in this?

Thanks

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If you can assume gas is isothermal at same temperature as solids and you don't care about the convective flow in the gas, then you don't actually need to model it explictly. Just calculate the pressure of the gas from a suitable equation of state and impose this as your temperature dependent loading on the inner surface of the tube. If the tube expands enough to change the gas volume significantly you may need to do this a little more carefully where you calculate the gas domain volume as part of the solution through a coupling variable and thus make the loading boundary condition depend on this volume.

If on the other hand you do care about the thermal and fluid dynamic response of the gas in the tube then you need to add nonisothermal flow application modes in the gas domain and solve for natural convection (they are weakly compressible NS and general heat transfer). This latter approach becomes much more difficult to implement- so unless you really need it I recommend you follow the first approach above.
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It works perfectly that way.

Thank you, Ozgur!