Porous Material With Liquid + ANSYS FLUENT

[eroque]

Hi,

So, i am trying to model a porous material with water in its pores.

This material will be subjected to a range of tempeartures and the water will solidificate and melt over the cycle.

Is there any way to model this ? Any way to model a porous material and then specify the proprieties od the water (specific heat, melting point, etc).

Thank you very much in advance

 

[hendersdc]

I don't know if Fluent can specifically model freezing or not. There may be ways to get the same effect as freezing using different parameters though. It would help if you explained what the goal of having the water freeze and thaw is.

The porous media options in Fluent will allow you to change the flow resistance to essentially zero by making the pressure drop prohibitively high and you can change the volume fraction of the porous section that is free vs solid but this will only affect thermal performance, not flow. Either way you will need to write a couple UDFs (user defined functions) in C that could take the local temperature and change the properties of the porous media depending on if the temp were above or below freezing.

I have not done too much related to this but the guys over at [URL unfurl="true"]https://www.cfd-online.com/Forums/[/url] will be able to help out with the details. A google search around "Fluent porous media" and "Fluent UDFs" will get you started.

 

[eroque]

Thank you hendersdc for your answer.

It is an academic problem. I want to study the inlfunce of the water in the concret pores.

I will simulate a temperatura variation cycle and the intention is to study see the water in solid and liquid state, as well as this influence in teh heat flux.

I was thinking in simulate a porous material with a very high flow resistance in order to keep the water statit in the pores. Another problem is to define the pores volume.

Do you have any specific tutorial or forum where i can learn this ?

Thank you in advance

 

[hendersdc]

I think your case may actually be relatively easy to study using the porous media options in Fluent since you are really only looking at the effect on heat flux instead of flow.

You could divide it into 2 different analyses, one with concrete and water, and the other with concrete and ice. It should be relatively simple to get the thermal properties to use as input for those. If you are really interested in what happens around the transition between solid and liquid it could be more difficult. Chapter 17 of the attached Theory Guide mentions solidification and melting but I have never used it, it also references a user's guide that I don't have.

My concern is that outside of defining the thermal properties of water and concrete I don't know how Fluent controls for the physical structure's effects on the overall thermal conductivity within the porosity feature. For example, does it just take a mass fraction of the overall for each material and put those resistances in series or does it somehow account for the interconnected nature of the pores where one material is a good conductor and the other is an insulator.

If you know the typical pore structure you could always create a really low level model where you physically model the pores for a small volume and compare it to the results from the bulk porosity approximation.

I have also attached the UDF manual to help if you need to write any functions.

 

[hendersdc]

Could only attach one file, here is the other one

 

[eroque]

Thank you very much for your answer.

Yes, i am really interested in what happens when the water changes phase. It is the main goal of the study, consider the phase change in the heat transfer.

The liquid is steady in the pores.

Thank you once again