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How to write variables in Phase Field Method

Posted Jan 10, 2022, 5:12 a.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD), Heat Transfer 3 Replies

Faisal Khan Computational Fluid Dynamics
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I am simulating water (disperse phase) droplet breakup in oil (continuous phase) flow in a T junction micro-channel. I went through comsole module application library and found a tutorial named "Droplet Breakup in a T-Junction". This problem is solved by level set method. In this model, variables are defined as V1, V2 (flow rate of fluid 1 and 2) and effective droplet diameter i.e. d_eff=2(intop1((phils>0.5)(x<-0.2[mm]))3/(4pi))^(1/3).

My geometry is a bit different (it has T branch in opposit direction) and I have constant value of flow rates for both fluids.

If I want to write the same expression of <d_eff> for phase field method, what changes will occur in this expression of effective droplet diameter. Itried with phils------->phipf but it didn't work at all.

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Faisal Khan
3 Replies Last Post Jan 13, 2022, 1:02 a.m. EST
Faisal Khan Computational Fluid Dynamics
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Posted: 3 years ago Jan 11, 2022, 12:57 a.m. EST
Updated: 3 years ago Jan 11, 2022, 1:01 a.m. EST

Here is the attached geometry with broader left side boundary is oil inlet and narrower vertical is water inlet. I want to input the following formula in local variable as attached in jpeg 2. It is giving me unit syntax error. I am unable to understand where is the mistake. In attached jpeg 3, I defined the globlal variables and some dimensions of the geometry. L is the channel length (800 micrometer). Experts, please help me.

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Faisal Khan
Here is the attached geometry with broader left side boundary is oil inlet and narrower vertical is water inlet. I want to input the following formula in local variable as attached in jpeg 2. It is giving me unit syntax error. I am unable to understand where is the mistake. In attached jpeg 3, I defined the globlal variables and some dimensions of the geometry. L is the channel length (800 micrometer). Experts, please help me.

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 3 years ago Jan 11, 2022, 5:48 a.m. EST

Hi,

I believe its a unit warning, as COMSOL has issues with fractional powers of units. Try to set your logic expressions in "unitless values" of the type (x[1/m] < L[1/m]) if L is defined with units, else just drop the units for your "parameter " (?) L .

Check if that helps.

Note a unit warning is not considered as an error, and calulation will go on, but it is a potential error, so the results might be wrong ...

Sincerely Ivar

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Have fun COMSOLing,
Sincerely,
Ivar
Hi, I believe its a unit warning, as COMSOL has issues with fractional powers of units. Try to set your logic expressions in "unitless values" of the type (x[1/m] < L[1/m]) if L is defined with units, else just drop the units for your "parameter " (?) L . Check if that helps. Note a unit warning is not considered as an error, and calulation will go on, but it is a potential error, so the results might be wrong ... Sincerely Ivar
Faisal Khan Computational Fluid Dynamics
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Posted: 3 years ago Jan 13, 2022, 1:02 a.m. EST

Thank you so much Dr. Ivar.

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Faisal Khan
Thank you so much Dr. Ivar.

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