Learning Forum

[Weiqiang Liu]

Hi all,

In my model, L-J parameters are imported for every species to calculate mass diffusion coefficients. In other words, kinetic theory is used to calculate diffusion. 

I have a porous zone in the domain. Therefore I want to define effective diffusion in this zone. The diffusion coefficients of species in porous zone is a combination of molecular and knudsen diffusion. The former is calculated by kinetic theory. In other fluid domain except porous zone, I want the diffusion coefficient to remain being calculated by kinetic theory.

However, in mixture material panel, there are three options for mass diffusivity: kinetic theory, constant and user-defined. My question is if I choose user-defined option to hook my UDF, will fluent still calculate mass diffusion coefficients for every species with kinetic theory? Because I need molecular diffusion coefficients calculated by fluent to yield effective diffusion coefficient in porous zone. 

Will fluent calculate molecular diffusion coefficient first with kinetic theory even I choose user-defined in mixture material panel?

Another question is :

After I defined diffusion coefficients in porous zone with UDF, how will fluent deal with mass diffusion in other non-porous zone. Because I did not define mass diffusion in non-porous zone in the UDF.

These confuse me very much.

Can anybody help me?

Best regards.

Weiqiang  

Best.

 

[Rob]

If you use a UDF you'll need to define the coefficient for both porous and non-porous regions. 

[Weiqiang Liu]

yes, another illogical thing is I need to use molecular mass diffusion coefficients calculated by fluent. This is impossible right? Unless I calculate by myself in UDF. Because fluent won't calculate any diffusion coefficients if I choose to use UDF to calculate mass diffusion coefficients.

Best 

Weiqiang

[DrAmine]

Yes you need to do all.

[Weiqiang Liu]

Thanks very much!! I can start now

Best.

[Modarres]

Hi Weiqiang,

I am working on a hybrid rocket combustion chamber, I need to write a UDF to add a mass diffusivity from wall to the adjacent flow, and also to define the heat transfer from flame to the wall which is the combustion chamber itself,

May I ask your help if you can share your UDF,

 

I appreciate for your guidance and support

Bests

 

 

 

Hi all,

In my model, L-J parameters are imported for every species to calculate mass diffusion coefficients. In other words, kinetic theory is used to calculate diffusion. 

I have a porous zone in the domain. Therefore I want to define effective diffusion in this zone. The diffusion coefficients of species in porous zone is a combination of molecular and knudsen diffusion. The former is calculated by kinetic theory. In other fluid domain except porous zone, I want the diffusion coefficient to remain being calculated by kinetic theory.

However, in mixture material panel, there are three options for mass diffusivity: kinetic theory, constant and user-defined. My question is if I choose user-defined option to hook my UDF, will fluent still calculate mass diffusion coefficients for every species with kinetic theory? Because I need molecular diffusion coefficients calculated by fluent to yield effective diffusion coefficient in porous zone. 

Will fluent calculate molecular diffusion coefficient first with kinetic theory even I choose user-defined in mixture material panel?

Another question is :

After I defined diffusion coefficients in porous zone with UDF, how will fluent deal with mass diffusion in other non-porous zone. Because I did not define mass diffusion in non-porous zone in the UDF.

These confuse me very much.

Can anybody help me?

Best regards.

Weiqiang  

Best.

 

[Weiqiang Liu]

Hi,

I have not logged in for a very long time. My project is different with yours. You want to define mass diffusivity from wall to adjacent fluid. Is it equivalent to surface reaction of wall surface? 

Regarding to heat transfer from flame to wall, I think it’s just a conjugate heat transfer issue.

Best 

Weiqiang