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Multiphase, multicoomponents strange “error” – mass fractions not balanced.

    • Diogo Martinho

      Hey all, 

      I will try to explain this shortly: 
      I have two phases, liquid and gas. Liquid has 5 different components, gas has 3 different components. So, in my opinion I have two different background species. One for the liquid phase, one for the gas phase. 
      All my domains are porous. However, no capillary pressure, contact angle, relative permeability is being defined. Only porosity and permeability of the domain. 
      While the liquid phase runs well and the results seem to make sense, when I look at the secondary phase the same does not happen. 

      The idea is the system will reach some concentrations and then there will be some phase change. So, when I initialize, two species (resulting from governing equations) are set to 0 mass fraction in the gas phase. Then, I would expect to have the third one (last species) to be 1 and to be solved algebraically. However, after two iterations something strange starts to happen (see figures). the simulation runs but in the centered domain the results show a non-balance in terms of mass fraction. 

      Any comments? 

      Kind regards,


    • SRP
      Ansys Employee


      The strange behavior you're observing may be due to various reasons, such as numerical stability, boundary conditions, or issues with your phase change modeling. Verify that your numerical solver and time-stepping scheme are stable for the given problem.Ensure that your boundary conditions for the phases and species are correctly set up.

      Thank you.

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