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Modelling Radiation Heat Transfer with Vacuum Component

Posted 09.07.2018, 15:03 GMT-4 Heat Transfer, Materials Version 5.3 3 Replies

William Deo
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Hello All,

I am modelling a geometry of two concentric cylinders (made of different materials) with a vacuum between the two cylinders in Comsol Multiphysics. I've been able to setup the geometry by creating three concentric cylinders and using a 'difference' to extract the middle cylinder. By doing this, my assumption was that this would lead to vacuum properties in the intermediate region when conducting my radiation diffuse surface simulations.

I searched through the materials library and vacuum is not an option, so I assumed that this is the most effective way to do this. However, the produced results were rather unexpected.

Please let me know if what I am doing here seems correct or if there is something that I've failed to understand and missed along the way.

3 Replies Last Post 02.11.2018, 16:30 GMT-4
Johan Cazals
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Posted: 6 years ago 10.07.2018, 08:07 GMT-4

Hi William,

I don't know if not putting anything between your two surface is fine, but for the surface to surface radiation module, you don't take into account any participating media (which can be taken into account by the module for radiation in participating media). So basically it just takes into account that you have two surfaces exchanging radiation between each other, taking into account their geometry, and the media is considered as vacuum for its optical properties no matter what in those conditions because it doesn't participate.

Johan

Hi William, I don't know if not putting anything between your two surface is fine, but for the surface to surface radiation module, you don't take into account any participating media (which can be taken into account by the module for radiation in participating media). So basically it just takes into account that you have two surfaces exchanging radiation between each other, taking into account their geometry, and the media is considered as vacuum for its optical properties no matter what in those conditions because it doesn't participate. Johan
Jeff Hiller COMSOL Employee

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Posted: 6 years ago 10.07.2018, 08:49 GMT-4

Here you will find a basic tutorial on surface to surface radiation:

https://www.comsol.com/model/radiation-in-a-cavity-447

Best,

Jeff

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Jeff Hiller
Here you will find a basic tutorial on surface to surface radiation: https://www.comsol.com/model/radiation-in-a-cavity-447 Best, Jeff
Yogesh Bhusal
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Posted: 6 years ago 02.11.2018, 16:30 GMT-4

Hi William,

I don't know if not putting anything between your two surface is fine, but for the surface to surface radiation module, you don't take into account any participating media (which can be taken into account by the module for radiation in participating media). So basically it just takes into account that you have two surfaces exchanging radiation between each other, taking into account their geometry, and the media is considered as vacuum for its optical properties no matter what in those conditions because it doesn't participate.

Johan

Hi Johan, I have the similar problem. I tried not putting any material between the two cylinders. But it gives a error that material has to be defined in the space. How do I solve that.? I applied air to the space coz they dont have vacuum medium in comsol, but I actually donot want air. I have trying to model heat transfer in vacuum. (Solar Collectors)

>Hi William, > >I don't know if not putting anything between your two surface is fine, but for the surface to surface radiation module, you don't take into account any participating media (which can be taken into account by the module for radiation in participating media). So basically it just takes into account that you have two surfaces exchanging radiation between each other, taking into account their geometry, and the media is considered as vacuum for its optical properties no matter what in those conditions because it doesn't participate. > >Johan Hi Johan, I have the similar problem. I tried not putting any material between the two cylinders. But it gives a error that material has to be defined in the space. How do I solve that.? I applied air to the space coz they dont have vacuum medium in comsol, but I actually donot want air. I have trying to model heat transfer in vacuum. (Solar Collectors)

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