## Fluids

#### How describe natural convection inside a closed volume

• giovanni_ianziti
Subscriber

hello,

I`ve a closed volume (heat pipe) with inside a part of water liquid and another part of mixture: air and vapour (when the water is boiling).

In my simulation I don`t have a good representation of the convection. the results are similar to the symmetric case but I`m working with a planar case.

how can I improve the convective movement inside the volume?

thank you

• DrAmine
Ansys Employee

1/Work with compressible liquid for liquid and ideal gas for mixture

2/Apply gravity and set an operating density

3/More details of your case are really welcome so that we can point to some modifications: detailed screenshot of the problem.

• Rob
Ansys Employee

Just to add, I don't think compressible liquid has a temperature term for density (check documentation) so if the system has a reasonable gas volume use a polynomial for liquid density.

• giovanni_ianziti
Subscriber

I`m working with these materials, but I`ve same problems to insert the all mixture properties. I`m using incompressible ideal gas for the mixture with  a pressure of 20000Pa and initial temp of 25 C. the gravity is active.

thank you

• Rob
Ansys Employee

In a confined space you'll need to use an ideal gas: if the density within the system changes but the volume cannot the solver will struggle.  If you have openings then it's not a problem.

However, as you've set water with a constant density you won't see any motion in the water due to natural convection within the water.

• giovanni_ianziti
Subscriber

In my work I have a non-compressible condition to respect for the flow. Can I lose this condition If I use ideal gas for the mixture?

• Rob
Ansys Employee

Yes. As it's a sealed system something must compress as the mass has to go somewhere.