CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   bc/wall/thermal - temperature not-constant? (http://www.cfd-online.com/Forums/fluent/50669-bc-wall-thermal-temperature-not-constant.html)

 martin February 24, 2009 18:29

bc/wall/thermal - temperature not-constant?

(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.

 Ashish February 25, 2009 04:42

Re: bc/wall/thermal - temperature not-constant?

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 ?

 Ralf Schmidt February 26, 2009 07:39

Re: bc/wall/thermal - temperature not-constant?

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

 martin February 26, 2009 10:20

Re: bc/wall/thermal - temperature not-constant?

thanks, that's not what I wanted to hear but at least now I know how to make it work...

 martin February 26, 2009 10:30

Re: bc/wall/thermal - temperature not-constant?

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.

 phiz March 1, 2009 12:33

Re: bc/wall/thermal - temperature not-constant?

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 :)