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bc/wall/thermal - temperature not-constant?

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Old   February 24, 2009, 18:29
Default bc/wall/thermal - temperature not-constant?
  #1
martin
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(fluent 6.3.26)

I'm looking for a way to calculate heat transfer to a wall including the rise of the wall temperature (unsteady). The case looks like that:

adiabatic isolation | aluminium wall (0.01 m) | fluid (0.1 m) | aluminium wall (0.01 m) | adiabatic isolation

The fluid will become hot so it should be cooled by the wall. The wall should become warm (a little bit).

In temperature-mode the wall-temperature is constant. In Heat-Flux I don't see a way to set the initial wall-temperature. I tried adding a bunch of "solid" cells but this won't solve the problem as adjacent zones can't have different materials.

Also "Users Guide - 7.13.4 Heat Transfer Calculations at Wall Boundaries" omits wall thickness for all options so I have no idea what to do.
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Old   February 25, 2009, 04:42
Default Re: bc/wall/thermal - temperature not-constant?
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Ashish
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i think u should explain problem a bit more i assume that "fluid is getting cooled as it loses heat to walls"

how you are defining it in terms of bc, can u explain pls ?
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Old   February 26, 2009, 07:39
Default Re: bc/wall/thermal - temperature not-constant?
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Ralf Schmidt
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Hi!

The thickness of the wall does NOT have any meaning for cooling problems!

You have to define two domains: one fluid and one solid. With a SINGLE wall between them.

Now, you set the initial temperature: solve - initialize-patch. Select the solid and patch the temperature you want.

The BC for the wall between fluid and solid (both: "wall" and "wall-shadow") is coupled.

(you have to consider the other BC for the other sides of your solid)

Thats it!

Best wishes Ralf
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Old   February 26, 2009, 10:20
Default Re: bc/wall/thermal - temperature not-constant?
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martin
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thanks, that's not what I wanted to hear but at least now I know how to make it work...
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Old   February 26, 2009, 10:30
Default Re: bc/wall/thermal - temperature not-constant?
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martin
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I tried setting wall temperature to 300 K. Now the (hot) Fluid will become cooler but the wall temperature won't change. So after some (infinite) time everything will be at 300 K instead of some (higher) mixing temperature.

In the other message Ralf told me, walls have no variable Temperature. I need a row of solid cells and a wall between fluid and solid to do that.
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Old   March 1, 2009, 12:33
Default Re: bc/wall/thermal - temperature not-constant?
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phiz
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Hi,

I'm trying the same for a pure conduction problem only for solids, so no fluids are present. I was wondering, if I would use patch, would the other wall boundaries not apply? (I don't want to give in any, for I need Fluent to calculate these). So basically my question is what patching really means

Please review: http://www.cfd-online.com/Forum/fluent.cgi?read=64337

Thanks in advance
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