Fluids

Fluids

Droplet is not heating up, air around it is getting colder.

    • abdulrahmanElmenyawi
      Subscriber

      I am trying to simulate water droplet evaporation using ansys fluent.

      I have set up my domain as 2d axisymmetric. Droplet is suspended on a suspender with air around it.


      Air is still and I turned off gravity. Air temperature is 190 degrees Celcius and the droplet temperature is 30 degrees Celcius. I am using the Lee model and VOF approach. I set up 3 phases. Water liquid, water vapour, and air. However the droplet doesn't heat up to saturation temperature to start evaporating. If anyone could help me with that I would be grateful.

    • Rob
      Ansys Employee
      The first problem is that vapour and air aren't separate phases, they're a species mixture in the gas phase. Not sure about the rest, fix the phase/species part and see what happens.
    • abdulrahmanElmenyawi
      Subscriber
      Thanks for your answer
      Do you mean that I remove the air phase and keep only 2 phases?
    • Rob
      Ansys Employee
      Yes, one phase is water and the other a species mixture of air & water-vapour. The mass exchange then needs a little more care, but the panel will lead you through it.
    • abdulrahmanElmenyawi
      Subscriber
      I have done that, now I have just 2 phases, I checked the initial conditions in terms of volume fractions of the phases and they seem correct with the new setup, however I still have the problem of the water droplet not heating up, instead the area around it cools down.
    • Rob
      Ansys Employee
      What temperature did you initialise the system at? What is maintaining this temperature?
    • abdulrahmanElmenyawi
      Subscriber
      Air temperature is 190 Celcius
      Droplet temperature 30 Celcius
      And here are my boundary conditions Axis is the bottom horizontal edge since its axisymmetric
      Free stream is the top wall
      Wall is the semicircle suspender
    • Rob
      Ansys Employee
      Please repost the images - we (Ansys staff) are not permitted to open attachments.
    • abdulrahmanElmenyawi
      Subscriber
      I have solved the heat transfer problem, the suspender wall should be modelled as an adabiatic wall, that did the trick. However evaporation doesn't happen correctly, when I enable surface tension between water phase and vapour-air phase, the droplet starts to deform in weird way. Can you help me with the evaporation model? I am using the built in Lee model and surface tension value is 0.072 N/m
    • Rob
      Ansys Employee
      Pictures will help.
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