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-   -   Boundary conditions at Fluid Solid interface (CHT) (http://www.cfd-online.com/Forums/cfx/25686-boundary-conditions-fluid-solid-interface-cht.html)

michelle April 20, 2008 08:49

Boundary conditions at Fluid Solid interface (CHT)
 
hi,

when i am trying to solve CHT problems,following the tutorial "CHT in a heating coil",the boundary conditions at the interface have been automatically taken as "conservative interface flux". this boundary condiition is one of continuity of heat flux.

Is there any reason why continiuty of heat flux is a better boundary condition than Continuity of temperature? And what shud we have to do if we want to impose continuity of temperature at the Fluid solid interface?

secondly, I also noticed that we do not specify any boundary condition for velocity at the fluid solid interface. Does CFX assume "No slip" for velcoity at the interface?

Thanks and regards, MIchelle

andy2O April 21, 2008 04:06

Re: Boundary conditions at Fluid Solid interface (
 
Well, continuity of heat flux conserves energy, whereas continuity of temperature does not itself guarentee this! Most people (Newton, Bernoulli, etc...) are quite keen on conservation of energy :)

If there is no thermal resistance associated with the interface surface itself, then temperature will also be continuous across the surface. If you have a really good mesh, this should be reasonably obvious, but on a finite mesh there will always be some jump between (any) two cells if there's a heat flux.

"secondly, I also noticed that we do not specify any boundary condition for velocity at the fluid solid interface. Does CFX assume "No slip" for velcoity at the interface?"

Yes. I think you can see that by double clicking on the 'boundary condition' associated with the interface which CFX automatically places in the fluid domain once you have made the interface. However, I can't check that just now, so I can't be quite sure if it shows up clearly when you double click.

andy



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