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Droplet shrinkage / creation for phase field model

Posted 23.09.2017, 11:27 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Heat Transfer Version 5.2a 1 Reply

Hamed Keramati
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Hi folks, I'm modeling a two phase (laminar) flow in COMSOL 5.2a. When I am using non-conservative form for the phase field, small droplets disappear, i.e. droplet shrinkage. When I turn the conservative form on some droplets are being created at one of the inlets! Does anybody have any idea about the source of this problem?

Thanks in advance for your help.

Hamed

1 Reply Last Post 24.09.2017, 03:57 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 7 years ago 24.09.2017, 03:57 GMT-4

Hi

Well the phase filed method is known to have issues with mass conservation for coarse meshes (reminder meshing is your discretisation hence a good measure of the relative precision of your conservation variables, high gradient => you need fine mesh to resolve it), this is due to the integration method that needs many elements to remain well defined and precise.

So my suggestion wouls be to improve (make finer) your mesh in the region of the phase transition zone. There are also the internal mesh refinement methods, check how to turn them on, unfortunately (at least in early 5.2 the mesh refinement did not take into account the velocity vector of the phase transition zone, so it sometimes did not anticipate where the phase frontier is going, hence a bit more mass loss).

-------------------
Have fun COMSOLing,
Sincerely,
Ivar
Hi Well the phase filed method is known to have issues with mass conservation for coarse meshes (reminder meshing is your discretisation hence a good measure of the relative precision of your conservation variables, high gradient => you need fine mesh to resolve it), this is due to the integration method that needs many elements to remain well defined and precise. So my suggestion wouls be to improve (make finer) your mesh in the region of the phase transition zone. There are also the internal mesh refinement methods, check how to turn them on, unfortunately (at least in early 5.2 the mesh refinement did not take into account the velocity vector of the phase transition zone, so it sometimes did not anticipate where the phase frontier is going, hence a bit more mass loss).

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