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-   -   Need help to define Boundary condition (http://www.cfd-online.com/Forums/fluent/101346-need-help-define-boundary-condition.html)

Chirag2302 May 2, 2012 00:07

Need help to define Boundary condition
 
Hello,

I have wall as fluid -solid interface means two sided wall. (wall and its shadow wall in FLUENT).

I have a known temperature gradient on that wall and known heat transfer coefficient for convection heat transfer condition.

Wall has solid as its adjacent cell zone and its shadow has gas as its adjacent cell zone.

As I know, temperature gradient can be define using UDF which is constant with respect to time. Now I want heat transfer between solid and gas

with known fixed value of heat transfer co-efficient.

How to define the boundary condition in the above situation in FLUENT...????

Can anyone help me..????????

Thank you...

LuckyTran May 2, 2012 13:05

an interface is not a boundary. You cannot apply boundary conditions to it. You can only apply boundary conditions to boundaries.

Chirag2302 May 2, 2012 23:43

2 Attachment(s)
Hello LuckyTran,

Yes, you are right that boundary condition can not be given to interface.

It was my mistake that i have written it as interface.

Actually it is the wall inside the computational domain.

One side of this wall has gas (fluid) and on another side of wall it is solid zone.

So,it is two sided wall. I have define it as a wall in GAMBIT and when I read mesh file in FLUENT it will generate the shadow wall automatically.

Now, I have the known temperature gradient on the wall which is steady with respect to time and known convection heat transfer coefficient for convective heat transfer between solid and gas.

In FLUENT, only three conditions are available for the case of two sided wall.
1) heat flux
2) temperature
3) coupled wall

Here, in my case i know the temperature gradient in my case. So, by using UDF, I can give temperature gradient on wall but how can i model convection between Solid and Gas???????????

You can see the attachment for more clarification.

Red color indicates stack (Solid zone) and light color indicates gas zone.

If you want any more clarification, you are always welcome.

Thank you.....

LuckyTran May 3, 2012 00:01

Quote:

Originally Posted by Chirag2302 (Post 358989)
In FLUENT, only three conditions are available for the case of two sided wall.
1) heat flux
2) temperature
3) coupled wall

Here, in my case i know the temperature gradient in my case. So, by using UDF, I can give temperature gradient on wall but how can i model convection between Solid and Gas???????????
Thank you.....

You cannot apply a heat transfer coefficient to a two sided wall because it is not a boundary. There's no such thing as applying boundary conditions to anything but boundaries. Two sided walls are not boundaries, they are interfaces. Stop treating it as an interface and treat it as a wall if you want to apply a convective condition.

Chirag2302 May 3, 2012 00:38

Hello LuckyTran,

Thank you for your guidance.

I am not able to do this, Can you explain more in detail how to model the above problem?

Thank you again for valuable time........

delaneyluke May 7, 2012 02:30

You don't need to specifiy an HTC at the solid-fluid interface since you are modeling both of them. Define the wall as a "coupled wall" and the solver will determine the HTC.

Regards
Luke

Chirag2302 May 7, 2012 06:51

Hello Luke,

Thanks for guidance.

Regards,

Chirag.


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