Fluids

Fluids

Condensation – Inverted Phases Give Different Results

    • Luuuca94
      Subscriber
    • DrAmine
      Ansys Employee
      Please insert the images instead of attaching them.nAre you saying that if you use water as the secondary phase (the phase being solved for) you are getting the expected condensation rate? nCan you report about convergence? n
    • Luuuca94
      Subscriber
      Yes, If I use water as the secondary phase, the condensation rate matches the heat extracted from the base plate. If I choose vapor as the secondary phase, the condensation rate is about 10 to 20 times higher than what is expected by looking at the heat extracted from the base plate. nConvergence criteria have been set to 10-3 for continuity, momentum and volume of fraction equation and 10-6 for energy equation. Every timestep the convergence criteria have been fulfilled. Global courant number was set to 0.25. nHave you got any idea what could cause this mismatch?nBy setting water as the secondary phase, the simulations take significantly more time and computational power to reach the same amount of condensed water. nI insert the images:nn
    • DrAmine
      Ansys Employee
      And did you change the mass transfer? I mean have you changed the from phase and the to-phase. nFor sure there is a difference as you now solving for the condensing phase and not treating it as a ballast phase. In your first case you are solving the transport equation of the the gas /steam. The volume fraction of liquid is interpreted from it. (compatibility condition). nI am however not expecting that the difference will be so dramatic. For that reason are you sure you are using the same same setup? Especially the mass transfer and contact angle (the latter should change if you change the phases order).n
    • Luuuca94
      Subscriber
      No, I did not change the mass transfer options in the two cases. In both cases I have set water as from phase and vapor as to phase. This might seem counterintuitive, but setting vapor as from phase and water as to phase results in convergence issues, especially in the case where water is the secondary phase. All the other settings were identical, including condensation-evaporation frequency. nThe contact angle has been changed, correct. In the case where water is the secondary phase the CA was set to 120°, while for vapor as the secondary phase the CA was 60° (180° - 120°). n
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