Learning Forum

[Sepehr Mostafayi]

I am getting zero diffusivity error in Fluent whenever I am trying Kinetic Theory for diffusion. My model is Mixture multiphase with two species mixture. L-J values are not zero for any species. 

[Rob]

It should work fine. Please can you post some images of the species & phase set up. 

[Sepehr Mostafayi]

[Rob]

What's in the liquid phase? Did you set the various L-J values in the species under the mixture-template(s) or Fluid? 

[Sepehr Mostafayi]

The liquid phase is water, ethanol and propanol, the L-J parameters are the default values from Fluent.

[Sepehr Mostafayi]

Also, the problem is with the gas phase, as the error comes with the activation of kinetic theory in the gas phase 

[Rob]

I assume temperature & pressure values are sensible? 

[Sepehr Mostafayi]

Atmospheric pressure and 25C temperature. 

[Rob]

And that's set in the operating & boundary conditions? 

[Sepehr Mostafayi]

Yes it is 

I don not think it is because of the boundary conditions, it gives the error as I activate the kinetic theory option.

[Rob]

As you activate? Have you added any materials from a User Database or are you just using the default Fluent database?

[Sepehr Mostafayi]

I am just using fluent database as I shared with you in the previous screenshots. I have received this error in several other different cases, it is confusing.

I mean whenever I activate the kinetic theory option I receive the error, I do not think it is because of operating or boundary condition. 

[Rob]

Molecular weights are non-zero? 

[Sepehr Mostafayi]

I am using the default Fluent materials, and I am not changing anything. Molecular weights are non-zero for all materials.

 

[Rob]

I checked with a colleague who routinely uses the option without any issues, I'm not sure I've ever used it. Which version of the code are you using? It may not be suitable for multiphase, but it's not mentioned as a limitation. 

[Sepehr Mostafayi]

Thanks, I am currently using Fluent 18

[Rob]

That may explain it: please update to 2024R1 and try there.