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-   -   Model foaming process: change the volume / density (http://www.cfd-online.com/Forums/cfx/26682-model-foaming-process-change-volume-density.html)

 pmp77 November 18, 2008 10:53

Model foaming process: change the volume / density

Hi Everybody reading this,

As a bit similar to Jervds' problem, I tought it is better to ask now, if you have any idea about this:

Just started to try to model the poliurethane foam curing. It expands significantly and solidifies. I managed to change the viscosity depending on time of residence (I have posted a question as well, a few days before), now I am only trying to increase the volume of the liquid Pur in a mould (for simplicity a box).

Here is my theoretical idea about how i will try: (Do not laugh, since I am new to cfd and cfx)

I give big thermal expansivity coefficient to my material and give a super thermal conductivity. I change the wall temperature in time, my material gets warmer quickly and expands.

Yet I have run only some coarse probe without any good result. I use a two phase model (Pur/Air 25C)I have my box filled to 25% with Pur at the bottom. No inflow. After 0.5[s]I increase the wall tempreature from 315K to 316K. My fluid gets warm instantly (from 315 to 316 K) then "flies" up to the top of the box as if it were lighter than the other phase (air 25C) The thermal expansion is set to 2 K^-1, so as far as I imagine it should double its volume and still remain at the bottom, since its original density is 1110 kg m^-3. The volume does not seem to change at all.(At least I can not see it.)

Later on, I would like to use real thermal processes and give thermal expansion a more complex function to simulate real expansion rate.

I try this way because foaming is a function of time as well, and I can not apply that to density.

>>For example, density can be a function of pressure (p), temperature (T) and location (x, y, z), but no other system variables.<<

Have you tried / Do you have any idea of modeling a self-expanding fluid? Maybe I started in the wrong direction.

Thank you for your time reading my problem.

All the best: Gergely

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