Discussion Forum

Hi

I have problems understanding your approach, air being a gas, and not a solid, you express the expansion via the pressure change for a given volume, no ?

and this pressure change is applied to the walls of your tube as normal forces over the area, no ?

I would restart by writing out the items used, their physical properties, how they interact, then the differential equiations impled and then only start to select applications mode in COMSOL

Good luck
Ivar

Sure, Air is a gas but I found thermal expansion only in the solids application. Which application should I use for expansion of gases?

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.

It works perfectly that way.

Thank you, Ozgur!