Fluids

Fluids

Difference between modeling homogeneous binary mixture and defining two fluids separately

    • abbas
      Subscriber

      Hello


      I am simulating CO2 in vortex tube. At the inlet, I have a gas phase CO2 but at the outlet, I have both liquid and vapor phases. I define these two phases separately with RGP table as a liquid and vapor RGP. After that, I use the homogeneous binary mixture which contains both phases. Therefore I have just one fluid which named CO2mix.



      Therefore in Domain I have one fluid.


       



       


      My question is: what would be a difference if I use both material (CO2 vapor and CO2 liquid) in default domain. 



       


      Best regards


      Abbas


       

    • seeta gunti
      Ansys Employee

      Hi Abbas,


      What happened to the mixture material properties? If you are defining two different fluids means there don't mix or meet at all?


      If the cell has both vapour and liquid, how the solver will calculate?


      Regards,


      Seeta


       


       

    • DrAmine
      Ansys Employee

      If you leave two fluids in your domain specification then you need to use an explicit multiphase model. Using the binary mixture you are just solving for the component fraction. 


       


      You need to tell us what you want to model: equilibrium or non equilibrium phase change? Do you have slip? 

    • abbas
      Subscriber

      I have an inlet that is vapor phase and at the outlet, I have vapor and liquid phase. As far as I know, there should be some liquid drop at the outlet. I think that because my main domain contains vapor so I can use continues fluid for vapor and droplet (phase change) for liquid. 


       


      Best regards,


      Abbas

    • DrAmine
      Ansys Employee

      Hi Abbas,


      Even with HBM you can handle multi-phase cases with phase change. So you need at first to figure out which flow regime are you expecting. Based on that you can just rely on HBM (equilibrium phase change = inifinite mass transfer) or do it within a non-equilibrium assumption (non finite mass transfer).


      In CFX you can even have homogeneous flow (single velocity field) but with non-homogeneous heat transfer. Please go through the tutorials and manuals. 


      I recommend attending a multiphase training.

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