Fluids

Fluids

natural convection film boiling on a sphere using VOF in fluent

    • Mahi97
      Subscriber

      Could someone help with the procedure of how to simulate the film boiling on a heated sphere at 1063K and the surrounding water at saturation temperature.There is initially a thin vapour film over the sphere and with time it enlarges and gets dispersed as a bubble. please someone help if possible.

    • Rob
      Ansys Employee
      Multiphase model is needed and phase change.
    • Mahi97
      Subscriber
      Can we do it by the VOF model and is any UDF required or just the evaporation-condensation mass transfer enough ?
      Can you please describe the steps to be followed using the VOF initializing with a thin vapour film around the sphere ?
    • Rob
      Ansys Employee
      Check the evaporation/condensation model to ensure it'll work. The evaporation side should be OK, but the condensation may get messy as the bubbles shrink. You may want the multi-fluid VOF. To get the vapour film you'll need to patch the vapour into an adaption register or cell zone.
    • Mahi97
      Subscriber
      Yeah, I have done that...the patching part ..and also included the multi phase vof ...taken two phases namely water and vapor , but my heat transfer coefficient is becoming very large in the order of some 10,000 but it should be in the range of 250 or something like that.Also my simulation is correct,but it is achieved slow compared to a similar research paper with this problem.
    • Mahi97
      Subscriber
      Sir, i have attached the case of the problem that Iam trying to simulate.Please suggest if i could do anything to get my results correct.
    • Rob
      Ansys Employee
      Check the HTC is calculated using the same reference values: it's a common oversight. As for the rest, assuming the mesh is good, what else is different compared to the paper. If you recall from the rules, staff are not permitted to open attachments.
    • Mahi97
      Subscriber
      Iam using the same reference values as that in the paper.Could I somehow send that paper to you, by mail or something because my problem would be clearer to you, if you'd see that paper.
    • Rob
      Ansys Employee
      No, we're not permitted to: please read the rules to understand what we can and can't do.
    • Mahi97
      Subscriber
      Sir, I have a small query.In my problem IAM intializing a vapour film around the sphere ,but after certain time steps the vapour film is getting detached completely and is getting formed again and that's the reason for the sudden jump in heat transfer coefficient.Is there a way to maintais a constant vapour film around the sphere and still be able to produce bubbles around it.
    • Rob
      Ansys Employee
      You'll need to set boundary conditions that support the film. The film is detaching as that's what the solver thinks is the correct answer based on your boundary conditions. Note, if the mesh and other settings aren't suitable that may not be physically what we'd expect.
    • Mahi97
      Subscriber
      Thanks a lot for the reply, but what are the boundary conditions to be set for the film and how can we set them, since I'm patching a certain region to be a vapor film and intializing it.So, how can we setup appropriate B.C , so that the vapor film doesn't detach completely.
Viewing 11 reply threads
  • You must be logged in to reply to this topic.