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-   -   solidification and melting with VOF: how to sink solid PCM as it melts? (http://www.cfd-online.com/Forums/fluent/112267-solidification-melting-vof-how-sink-solid-pcm-melts.html)

sakil2k3 January 24, 2013 23:27

solidification and melting with VOF: how to sink solid PCM as it melts?
 
Hi all, I have an enclosure spherical glass that is contain with phase change material (PCM) that is in its solid state initially. Heat will be applied above the melting temperature of the PCM around the spherical glass. During the melting process of the PCM there will be 2 phases present in the enclosure, the liquid and solid state. The solid PCM will drop to the bottom due to the gravitation force.

A 2d mesh was created and exported out from Gambit.

In Fluent, I used Solidification and Melting function in my simulation with VOF. All Material properties of the PCM and glass have set accordingly. The Gravity was also enable with Y=-9.81 in the Operating Condition and the Variable-Density Parameters was also set to an operating density of PCM, that is 777kg/m^3. The Body force weighted under Discretization in Solution Control was also selected.

After iterating for 200 sec, the values for the Liquid fraction was calculated but the simulation did not show the solid PCM sink to the bottom of the enclosure.

How can I make the solid PCM to sink to the bottom as it melts?
Thanks.:D

msaeedsadeghi January 26, 2013 00:57

I have done that. It's easy, you may have done a great mistake.

sakil2k3 January 26, 2013 03:52

Quote:

Originally Posted by msaeedsadeghi (Post 404133)
I have done that. It's easy, you may have done a great mistake.

Pls can u tell me where is the mistake. I m a M.Sc student and it is very urgent to complete my Thesis. Pls tell me how to do it. I will be ever grateful to you.
Thanx

msaeedsadeghi January 26, 2013 04:00

It should be checked

sakil2k3 January 26, 2013 04:25

1 Attachment(s)
Thank you for ur replay.
I have attached the full procedure and strategies.
I am eagerly waiting for ur replay.
Thanx

sakil2k3 January 28, 2013 04:30

Please can anyone help me???

beer January 28, 2013 10:23

Hi
Of course the solid region doesn't move, the moment source holds it back. I would try to add a source term for gravity and use (U(n)-(n-1)) instead of U, where n is the timestep. I think with this modifications the source your solid reagion will sink to the bottom.

Greetings

coolmen_21 February 13, 2013 16:56

solidification and vof
 
I have a similar problem, can you send me your file . cas, to check on my side

Mahboobe365 January 14, 2014 13:05

Dear Saeed Sadeghi,

It seems that you are so happy knowing every thing and not helping others!

msaeedsadeghi January 15, 2014 04:17

Quote:

Originally Posted by Mahboobe365 (Post 470017)
Dear Saeed Sadeghi,

It seems that you are so happy knowing every thing and not helping others!

Sorry, I am so busy.

thermal energy March 14, 2014 12:37

Hello dear friends,

I try to simulate melting process using VOF model. Pcm is solid phase initialy. Upper part of the solid there is air. They do not interpenetrate eachother. Natural convection is active. My primary phase air, secondary phase is pcm (phase change material). 85 % of volume is solid pcm initialy, 15% of total volume is air. I have some questions to be sure about my model.

First, I do not define interface between air and pcm. Mean, There are 3 cell zone: air, fin ,pcm but I do not create name selection for this interface in meshing. Is it ok?

Initial condition of Wholesystem temperature is 293K, but air temp is 300K. how to set air temp ?

For cell zone condition, all cell zone (air, pcm, fin ) show mixture. Also for example, if I change pcm to phase2, all of cell zone change to phase 2

Only for secondary phase (pcm), I patch within fluent by adapt-region-mark then patch. Ok? Value of volume fraction should be 1 or 0 while patching?? I am confused. Initialy pcm is solid.

For initial values phase-2 volume fraction is 0. Ok?

I did some iteration for a short time to check model. For results, in graphics-countors I can not see total temperature for phase 1 and 2 only entalphy values I see for phase1 and 2.

Also countors of solidification/melting it shows only mixture. Mixture show what?

Any interaction should I use like surface tension etc.

Thanks for your help. ı am in stuck.

HamidIran October 9, 2014 23:59

A large mushy zone constant enforces the velocity in solid phase to go to zero (or to pull velocity). If you set it to zero the solid phase will move with a velocity obtained from the solution of the N-S equations. However, it will deform like a liquid.

HyperNova December 13, 2014 09:59

Quote:

Originally Posted by Mahboobe365 (Post 470017)
Dear Saeed Sadeghi,

It seems that you are so happy knowing every thing and not helping others!

This who iranian are Mahboobe !!!

zbc19910519 December 21, 2014 10:25

Hi, would you please tell me more detail about how to acheive your idea to move the solid part, thx

Quote:

Originally Posted by beer (Post 404522)
Hi
Of course the solid region doesn't move, the moment source holds it back. I would try to add a source term for gravity and use (U(n)-(n-1)) instead of U, where n is the timestep. I think with this modifications the source your solid reagion will sink to the bottom.

Greetings

Hi can you tell some detail about how to accomplish your idea to move the solid part? thx

greetings

Quote:

Originally Posted by sakil2k3 (Post 403922)
Hi all, I have an enclosure spherical glass that is contain with phase change material (PCM) that is in its solid state initially. Heat will be applied above the melting temperature of the PCM around the spherical glass. During the melting process of the PCM there will be 2 phases present in the enclosure, the liquid and solid state. The solid PCM will drop to the bottom due to the gravitation force.

A 2d mesh was created and exported out from Gambit.

In Fluent, I used Solidification and Melting function in my simulation with VOF. All Material properties of the PCM and glass have set accordingly. The Gravity was also enable with Y=-9.81 in the Operating Condition and the Variable-Density Parameters was also set to an operating density of PCM, that is 777kg/m^3. The Body force weighted under Discretization in Solution Control was also selected.

After iterating for 200 sec, the values for the Liquid fraction was calculated but the simulation did not show the solid PCM sink to the bottom of the enclosure.

How can I make the solid PCM to sink to the bottom as it melts?
Thanks.:D

My friend , did you solve your problem?

Quote:

Originally Posted by coolmen_21 (Post 407675)
I have a similar problem, can you send me your file . cas, to check on my side

Hi, have you solved this problem?:o

beer January 2, 2015 19:11

Hi zbc19910519

Sure. Just use a very strong force, which is velocity dependent. For example 1e10*(vx-1) if you want your velocity component in x-direction to be 1. Just remember to tell the solver the derivative of this equation (I think it is called Source Coefficient in Fluent), otherwise the source will blow up your calculation. The solver uses the derivative to include the force in the implicit part of the solver (see Patankar).

Cheers

zbc19910519 January 3, 2015 01:36

Quote:

Originally Posted by beer (Post 525943)
Hi zbc19910519

Sure. Just use a very strong force, which is velocity dependent. For example 1e10*(vx-1) if you want your velocity component in x-direction to be 1. Just remember to tell the solver the derivative of this equation (I think it is called Source Coefficient in Fluent), otherwise the source will blow up your calculation. The solver uses the derivative to include the force in the implicit part of the solver (see Patankar).

Cheers

Thx, my friend, but if add a momentum source/sink in melting/solidification process, actually in which a huge momentum sink should be added to solid phase, thus, the solid phase is fixed, for the gravity is ignored compared to momentum sink, for example, if I initialize the case as the solid phase hangs in the air, and in next time step, it doesn't move any more and it is not mean to be, so how should I add this momentum sink properly to simulate the phase change process.

Thank you again !

beer January 3, 2015 07:51

I didn't really get what you're trying to say. Can you show a picture or something?

B.Hamada March 17, 2015 16:40

Question
 
how I can define the parameters of the liquid phase of PCM in Fluent initially solid.
Please help!!!!!!!!!!!!!!!!!!!!!!!!

HamidIran March 17, 2015 17:24

Hi Hamada,

Depending on the melting temperature that you define for your PCM in Materials tabs and the initial temperature you set in the "Solution Initialization" tab, the initial state of PCM is automatically determined. For example, if your PCM melting point is 309<Tm<311, if you set the initial temperature to 308, the PCM will start from solid phase. If your initial temperature is 312 the initial PCM phase will be liquid, and if the initial PCM temperature is 310, the initial volume fraction of liquid phase will be 0.5.

I hope this helps.

Hamid

B.Hamada March 17, 2015 19:54

Quote:

Originally Posted by HamidIran (Post 536849)
Hi Hamada,

Depending on the melting temperature that you define for your PCM in Materials tabs and the initial temperature you set in the "Solution Initialization" tab, the initial state of PCM is automatically determined. For example, if your PCM melting point is 309<Tm<311, if you set the initial temperature to 308, the PCM will start from solid phase. If your initial temperature is 312 the initial PCM phase will be liquid, and if the initial PCM temperature is 310, the initial volume fraction of liquid phase will be 0.5.

I hope this helps.

Hamid

Thank you
But i have a question, i have two data one for solid phase and the other for the liquid phase, for example there is a liquid density and a solid density, the same for the Specific heat capacity, and the Thermal conductivity.
but in fluent, I can enter the parameters of a single-phase.
please, what can i do?


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