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heat resistance on solid-solid interface

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Old   March 12, 2009, 06:32
Default heat resistance on solid-solid interface
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Bela
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Dear CFX users!

My problem is the following: there are two solid bodies which are connected with solid-solid interface. There is heat generation (W/m3) in either of the solid domains. The thermal conductivity of the solids is different. I should define an additional heat transfer coefficient (4000 W/m2K) because the thermal contact is not perfect between them. I don't know how to define this htc on the domain interface. I found that I could set up source, where the Flux coefficient is the htc, but I don't know the value of the Flux. Does anybody could help me?

Bela
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Old   March 16, 2009, 15:31
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Pratik Mehta
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Hi, could you please explain what do you mean by thermal contact is not proper . What exactly is your problem set-up .
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Old   March 19, 2009, 04:55
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Thermal contact resistances are not supported in ANSYS CFX 11. There may be some way of representing such resistances with user defined code or CEL though - it might be worth contacting ANSYS directly for advice.

I was told by ANSYS that they will be supported (together with other surface physics enhancements) in CFX 12, but I haven't seen the Beta release of CFX 12 to check whether they actually made it to the actual product...

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Old   March 19, 2009, 09:53
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You can use Fluent for solving this problem.

Quote:
Originally Posted by Bela
;92318
Dear CFX users!

My problem is the following: there are two solid bodies which are connected with solid-solid interface. There is heat generation (W/m3) in either of the solid domains. The thermal conductivity of the solids is different. I should define an additional heat transfer coefficient (4000 W/m2K) because the thermal contact is not perfect between them. I don't know how to define this htc on the domain interface. I found that I could set up source, where the Flux coefficient is the htc, but I don't know the value of the Flux. Does anybody could help me?

Bela
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Old   March 19, 2009, 12:11
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Pratik Mehta
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Hi,
Is your problem a natural convection or forced convection , all I can for now think of is that , you can have model the improper contact between the two solids as a porous media ( separate porous domain) , this porous domain should be having all the flow resistances in 3 directions.

I hope this helps

cheers
Pratik
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Old   March 19, 2009, 18:43
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Pratik,

When two bodies are held together, the (perhaps large, or perhaps microscopic) roughness of the surfaces of the bodies means that they do not come into uniform perfect contact. There will be small gaps between them (often filled with air). Therefore for heat to flow from one body to another it has to cross this small gap by conduction, small scale convection, or radiation. This gives rise to thermal resistance.

Because the gap is so small, you do not want to mesh it or model it as a 3-d feature. Instead, it is often modelled as a thermal resistance at a surface. Unfortunately CFX does not yet easily support this. This is what Bela was asking about.

I hope it makes sense now.

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andy2o
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Old   March 20, 2009, 03:28
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Pratik Mehta
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Hi Andy ,

ok, now it is clear abt Bela`s query , you are right CFX till now have no such feature till now

thanks andy

best regards
pratik
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