UDS for heat transfer (enthalpy method)

- May 22, 2020 at 3:57 am
  
  MHMD90
  Subscriber
  
  Hi,
  
  I want to model freezing of water in a solid matrix via ANSYS Fluent for which I have to use UDS. How can I define a UDS to solve the freezing problem with the enthalpy method? The Cp method is easy to set up, but it diverges as it approaches the freezing point.
  
  Attached is the unsteady term for the cp method which actually stands for dT/dt and is pretty much like Fluent manual suggests.
  
  The enthalpy method is more consistent and seems to smoothly pass the phase change area, but I don’t know how to define the scalar for the unsteady term. Because the unsteady term is dh/dt, but the diffusion term is αd²T/dt². The left-hand side is solving for the enthalpy (including both sensible and latent heats) and the right-hand side for the temperature. How can I relate enthalpy to temperature in the unsteady term?
  
  Kind Regards,
  
  MHMD
- May 22, 2020 at 6:00 am
  
  DrAmine
  Ansys Employee
  
  Ansys staff do look into attachments. You can insert the picture in the text.
  
  Fluent does incorporate the Enthalpy method in the Solidification and Melting Model.
- May 22, 2020 at 7:06 am
  
  MHMD90
  Subscriber
  
  Hi Amine,
  
  Thanks for the reply. Below is the picture for unsteady term UDF for the Cp method. I have tried the Solidification and Melting Model, but it doesn't work well for my case because it considers a linear function for liquid fraction in the phase change area (mushy zone) while in my model there's a more gradual phase transition requiring a non-linear function for the liquid fraction. That’s why I need to define a UDS. Finding the correct relation between enthalpy and temperature is tricky here. Any thoughts on this would be appreciated.
  
  Regards,
  
  MHMD
- May 22, 2020 at 9:02 am
  
  DrAmine
  Ansys Employee
  
  And what do you require now?