3 phases bubble column interface issue

    • Nicolas_CFD



      I am currently studying hydrodynamics of a bubble column and I have an issue when I want to simulate it with 3 phases. 


      Firstly, I studied the bubble column with only 2 phases (the column is filled with liquid tin, liquid height = domain height = 120mm, and methane is injected from the bottom part) and I did not have any problem with my simulation.


      Now, I want to study the impact of liquid height and how the interface moves. So I have to add another phase (air) to fill the domain. Bubble column's height is now 320mm, and liquid height is 120mm, so air height is 200mm. During the simulation, there is no problem when methane is injected in the liquid tin phase, but when methane arrives to the interface between liquid tin and air, it never goes through the interface. Methane is stacking at the interface and then just push out the air phase (I joined a picture of the situation to illustrate. Red phase is methane, green phase is liquid tin and blue phase is air).

      Here is a description of my set up :

      • 2D axisymmetric, transient
      • multiphase model : VOF, 3 phases : air, liquid tin, methane (I tried with and without surface tension)
      • energy on
      • turbulence model : k-epsilon RNG

      Boundary conditions :

      • Velocity inlet, turbulence : intensity and hydraulic diameter, methane volume fraction = 1 (0 for air)
      • Pressure outlet, turbulence : intensity and hydraulic diameter, air backflow volume fraction = 1 (0 for methane)
      • I have 2 walls with a fixed temperature

      As I thougth that the problem occured because of wrong backflow volume fraction, I tried every combinations of backflow VF, I tried every phases combinations too but I still have the problem.

      I have no more ideas on which parameter I can change to solve the problem. Maybe it is just because this kind of set up is not available with VOF model ?


      Thanks for the future answers


    • Rob
      Ansys Employee

      Why is methane not included in the air phase as a species? 

    • Nicolas_CFD

      Is it really mandatory for this study ? As I never used species transport model I do not really understand how to set up it, despite the fact that I checked the theory and user's guide. 

      I need to have liquid tin in the bottom of the bubble column and another phase (air) to fill the domain as it can not be empty, so I need a pure liquid tin phase. As I want to study rising methane bubble, so I need a pure methane phase.

      So the point is about the filling phase. Do I need to replace the air phase by a air-methane mixture ? Or I keep the air phase and I add another phase for the mixture ? I do not really understand what to do.

    • Rob
      Ansys Employee

      If you want the air and methane to mix, then yes you need to do it. If you just want a gas above the liquid tin why not make it methane? 

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