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PCM as a porous medium
Posted 16.12.2015, 11:11 GMT-5 Heat Transfer & Phase Change, Porous Media Flow 4 Replies
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Hello,
I am working on a heat storage where PCM it added to water. One way to add the PCM to the water is to use PCM spheres. Unfortunately is it not possible to model this in COMSOL because it is much to big.
Therefor I tried to model the PCM spheres as a porous medium.
What I want is a tank with water and PCM spheres at a temperature of 313 K and a inflow temp of 283 K. Then I want to measure what the outgoing temperature is.
I used for that the 'heat transfer in porous media' and the 'two phase Darcy's Law features.
But how do I indicate that the porous matricx is PCM and that it has a phase transition temp of 299K with latent heat of 190 kJ/kg?
When I just ad the feature 'heat transfer in phase change material' than the 'heat transfer in porous media' is not active any more.
Astrid
I am working on a heat storage where PCM it added to water. One way to add the PCM to the water is to use PCM spheres. Unfortunately is it not possible to model this in COMSOL because it is much to big.
Therefor I tried to model the PCM spheres as a porous medium.
What I want is a tank with water and PCM spheres at a temperature of 313 K and a inflow temp of 283 K. Then I want to measure what the outgoing temperature is.
I used for that the 'heat transfer in porous media' and the 'two phase Darcy's Law features.
But how do I indicate that the porous matricx is PCM and that it has a phase transition temp of 299K with latent heat of 190 kJ/kg?
When I just ad the feature 'heat transfer in phase change material' than the 'heat transfer in porous media' is not active any more.
Astrid
4 Replies Last Post 20.01.2016, 05:45 GMT-5
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Posted:
9 years ago
Dear Astrid,
You might want to take a look at our blog post on the subject of phase change.
www.comsol.com/blogs/phase-change-cooling-solidification-metal/
In essence you artificially add the latent heat to the heat capacity around the melting temperature. The built in interface does this for you, but you can also built this yourself.
The width of the function needs to be well resolved by time and mesh, and thus you might need some testing for the optimal settings.
There are several example models on this like:
www.comsol.com/model/phase-change-474
If your spheres are relatively big, you might also want to look at our feature "local thermal non-equilibrium" introduced in version 5.1:
www.comsol.com/release/5.1/heat-transfer-module
This allows for a separate temperature field for the spheres and the fluid.
Best regards,
Frank
You might want to take a look at our blog post on the subject of phase change.
www.comsol.com/blogs/phase-change-cooling-solidification-metal/
In essence you artificially add the latent heat to the heat capacity around the melting temperature. The built in interface does this for you, but you can also built this yourself.
The width of the function needs to be well resolved by time and mesh, and thus you might need some testing for the optimal settings.
There are several example models on this like:
www.comsol.com/model/phase-change-474
If your spheres are relatively big, you might also want to look at our feature "local thermal non-equilibrium" introduced in version 5.1:
www.comsol.com/release/5.1/heat-transfer-module
This allows for a separate temperature field for the spheres and the fluid.
Best regards,
Frank
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Posted:
9 years ago
I do not think that you understood my question. I know how to add a phase change material to my model. I did that before. I can make a model where water flows around a PCM sphere and where the heat transfer works good.
But know I would like to fill a tank of 1 meter hight with PCM sphere with a ratius of 11mm.
I can not do this in 3D because the model gets to big, it is possible in 2D but i do not think that that is accurate enough.
So I wanted to model it as a porous medium. So I use the 'heat transfer in porous media' feature. Where you can add the heat conduction and thermodynamics of the fluid (water) and the heat conduction and thermodynamics of the porous matrix. And now I want the porous matrix to be PCM. But when I add heat transfer with phase change to the heat transfer in porous media feature the heat transfer in porous media gets inactive.
So how can I combine these two features?
Attached a model without any numbers added.
Astrid
But know I would like to fill a tank of 1 meter hight with PCM sphere with a ratius of 11mm.
I can not do this in 3D because the model gets to big, it is possible in 2D but i do not think that that is accurate enough.
So I wanted to model it as a porous medium. So I use the 'heat transfer in porous media' feature. Where you can add the heat conduction and thermodynamics of the fluid (water) and the heat conduction and thermodynamics of the porous matrix. And now I want the porous matrix to be PCM. But when I add heat transfer with phase change to the heat transfer in porous media feature the heat transfer in porous media gets inactive.
So how can I combine these two features?
Attached a model without any numbers added.
Astrid
Attachments:
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Posted:
9 years ago
Dear Astrid,
I understand what you intend to do, and in your case it is not possible to combine these two built-in interfaces. However, you can implement the phase change phenomenon in the heat transfer in porous media interface. This is done in the same way as described in that blog post:
www.comsol.com/blogs/phase-change-cooling-solidification-metal/
Simply said, you can create a material that has different properties with respect to temperature, as shown in this model:
www.comsol.com/model/phase-change-474
Most important is the heat capacity, on which you add the latent heat of the phase change with a gaussian pulse with a certain width.
If you still have some questions on the implementation part, you can also contact support directly.
Best regards,
Frank
I understand what you intend to do, and in your case it is not possible to combine these two built-in interfaces. However, you can implement the phase change phenomenon in the heat transfer in porous media interface. This is done in the same way as described in that blog post:
www.comsol.com/blogs/phase-change-cooling-solidification-metal/
Simply said, you can create a material that has different properties with respect to temperature, as shown in this model:
www.comsol.com/model/phase-change-474
Most important is the heat capacity, on which you add the latent heat of the phase change with a gaussian pulse with a certain width.
If you still have some questions on the implementation part, you can also contact support directly.
Best regards,
Frank
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Posted:
9 years ago
Thanks for your response, I get what you mean now.
But unfortunately is the temperature distribution over time much different from when I model it with the heat transfer in fluid and in PCM features.
Can I change something in the setting so that it looks more the same?
When I model it for stagnant water than the results for the porous medium feature correspond very well with the 'real' situation.
see attached my file.
Kind regards,
Astrid
But unfortunately is the temperature distribution over time much different from when I model it with the heat transfer in fluid and in PCM features.
Can I change something in the setting so that it looks more the same?
When I model it for stagnant water than the results for the porous medium feature correspond very well with the 'real' situation.
see attached my file.
Kind regards,
Astrid
Attachments: