Fluids

Fluids

Evaporation of droplets

    • b404957074
      Subscriber

      Hi there,


      Is that possible to simulate the evaporation process in an air/water vapour mixture of a group of static water droplets on a big surface?

      Any suggestions will be appreciated

    • DrAmine
      Ansys Employee
      Yes it is possible. You might require some customization to do that for example using Hertz-Knudsen Mass Transfer. You can rely on DPM Model so treat the droplet settings as discrete mass points and just account for the mass and heat transfer with the gaseous mixture.
    • b404957074
      Subscriber
      Thanks for the reply.
      In the DPM case, to patch water droplets onto a surface, I have to specify that surface as a source of water droplets injection but set the velocity as 0 m/s. Is that correct?
      Cheers
    • b404957074
      Subscriber
      I thought DPM is just for injection. In my case, the droplets are static on the metal surface. How can I deposit the droplets onto the metal surface using DPM?
      Could anyone please help?
      Thanks!

    • DrAmine
      Ansys Employee
      Better to describe what you want to do and perhaps use some pictures or screenshots. If you are looking to free surface evaporation then DPM is not good. If you have something like thin film on a surface then we can still use a sort of thin film model.

      Which scenario do you have?
    • b404957074
      Subscriber
      Hi DrAmine I wanna simulate the evaporation process of a wet metal roof sheet. The condensation of the roof sheet is due to the overnight cooling. In reality, it should be in the form of droplets. Please see the pic down below.

    • Rob
      Ansys Employee
      OK, so it's more a film than droplets: have a look at the Lagrangian Wall Film and evaporation.
    • b404957074
      Subscriber
      Hi Rob Thanks for the reply. Can I ask why you say it is more a film than droplets?
      I have been struggling about if I should model this situation as droplets or film for a long time. I personally think treating them as droplets evaporation will be very hard or even impossible to achieve.
      Another question is why Lagrangian wall film but not eulerian wall film?
    • DrAmine
      Ansys Employee
      It is bit insane to model every single droplet on that roof and its evaporation. For that reason you rather start using a thin film model like LWF and incorporate evaporating. Later on you can modify the mass transfer law to incorporate any effects of distribution and shape. Prepare your self : that is a lot of research work :)

      If you just want to deal with 10 or 100 droplets evaporating: you can then resolve everything deploy VOF and incorporate the evaporation using User Defined Functions.
    • DrAmine
      Ansys Employee
      Or you start with resolved VOF film and keep track of pooling and droplet shedding from that film due to gravity. Afterwards you can start adding phase change.
    • b404957074
      Subscriber
      Thank you, all. I will give it a go!
    • DrAmine
      Ansys Employee
      Good Luck.
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