Discussion Forum

Hello together!
First of all I want to apologize for my probably bad English and some typos! I have a (some) COMSOL problem(s) and I need to discuss this with someone. First I’ll introduce me and my project after that I’ll describe you the problem(s) I’m trying to solve, so for those who are just interested in that, just skip the introduction.

Introduction
I’m student of Safety and Hazard Management at Otto-von-Guerike-University in Germany. To get my degree I need to write my master-thesis. My education about simulation-tools is little and my experience is even less. I worked with Fire Dynamic Simulator (FDS) for half an year and heard a course about ANSYS Fluent but did not use it.

Project
The topic of my Master-theses is to simulate the heat transport in Compressed Air Foams, especialy in firefighting foams. By now I’m sure about the geometry of the foam and some physical aspect’s I must consider. So now let’s get to the COMSOL questions.

COMSOL-SetUp and Settings

Geometrie
In general foams can have very complex geometries and vary, even under the same circumstances while production. The big advantage on my side is, that Compressed Air Foams (for firefighting applications) (CAFS) are so called structured foams with a quite narrow Distribution of bubble diameter. So most foams consist of 50µm bubbles in an bcc packing. I'm encounting first dufficulties in producing the Geometrie!

COMSOL
up.picr.de/27919330df.png <-Geometrie-Tree
This is an overview over the geometric node in COMSOL. I'll go through this and ask questions where I am unsure.
First the Result: up.picr.de/27919603sw.png
I started with one bubble of the size of 50µm...
up.picr.de/27919574ak.png <- Settings of the Initial Bubble
and used the array function to achieve a bottom layer
up.picr.de/27919619et.png <- Settings of the Array
After that I made a Union with all the bubbles to acchieve on strukture.
up.picr.de/27919671lg.png<- Union Settinggs
The bubbles where abstracted from a Block.
The block simulats the water in the foam.
This results in the first Geometrie!

Question: I want no Mesh and no callculation inside the bubbles. Did I acchieve that?
Explainaction: For the beginning I negelgt the heat transfer from the water to the bubbles because of the low heat capacity of the air. This results, in my opinon, in no need for a mash inside the bubbles. The shall be Walls for the flow and thermal insualtion for the heat transfer.

Question: How can I adulterate the overlaping of three or more bubbles to one strukture? I had no success with any of the Options in the Geometrie tab.
Any comments for the Geometrie so far?

Material
Again in general, the foam consists of water and air. So I added "Water" from the material tab. See teh Result: up.picr.de/27919828jt.png
Question: Why do I have 28 Domains? Did the Union-Thing not work? And what Material do I have to define guess Domain 2-28 are the bubbles. The should just be bounderys so actually they dont need any material?

Physics
In general I'm the opinion that I'm considering an non-isothermal Problem. As I'm investigationg the heat transfer in the foam I need a heat source that must be cooled and some foam. I'n my opinion there will be just natural convection and Marangoni convection in the foam.

COMSOl
To simulat the model in added "Laminar Flow" and " Heat transfer in fluid" to the physics and conected them with the Non-Isothermal flow multiphysics and added marangoni convection.
up.picr.de/27919916gn.png <- Non-Isothermal Flow
up.picr.de/27919917no.png <- Marangoni-Effect

The Laminar Flow Node is Set up like this:
up.picr.de/27919959lt.png
up.picr.de/27919960iu.png
up.picr.de/27919961gw.png
up.picr.de/27919962lt.png

Question: Which BC's should I probebly apply? On the sids I would use Wall/No Slip. Top Side is the big question! PLZ Help! At the bubbles I woud use Interior Wall?


Heat transfer node

The Setup of the Heat transfer in fluids Node
up.picr.de/27920045ry.png
up.picr.de/27920046cl.png
up.picr.de/27920047tt.png
up.picr.de/27920049ox.png

Question: Again I would apply "thermal insulation" to the bubble strcture and the Walls. The question is again the top side! There should be Environment. How do I model this?


Okay this so far. Please comment to the Setup and help me with my questions. After I completed the Setup I'll deploy the file here and would like to discusse about the solver. But for now ist late in Germany and I'm tired. I'll correct the typos tomorow.

Thanks and PLEASE help
so far Fabian!