[Lorenzo210]

Hi everyone,


I am using COMSOL 6.1 to simulate a droplet evaporation.


Geometry:
- 2D axis symmetric domain, 90degrees circle domain with R= 60*R_droplet
- Droplet initialized with its R_droplet and theta0 contact angle.


Physics:
- Laminar two phase flow with moving mesh;

- Heat tranfer in fluids;
- Transport of concentrated species;
- Transport of diluited species;

- Mathematical ODE for various calculations.


Multiphysics:
- Nonisothermal flow
- Marangoni effect
-Reacting flow


Problem: I tried to apply the Marangoni effect to the liquid-gas interface, but I cannot select the interface, only wall boundaries can be selected.


I am a bit confused because I took an identical model written in COMSOL 5.6 (not sure about the version), and the Marangoni effect can be applied to the interface.


The 5.6 Marangoni effect gives a warning that "This feature is obsolete and will be removed in future versions." so for that reason I am trying to use the new Marangoni effect version.


Has anyone any clue why the newest version cannot select the liquid-gas interface? The tutorial and the COMSOL documentation (user guide and similar) have not helped.


I was able to run successfully the older model enabling and disabling the Marangoni Effect, so the only issue is with the newest version.


Many thanks.


Regards,
Lorenzo

[Feeric]

You should be able to select your interface thanks to the Free Surface boundary condition that appears in the laminar flow physics, provided that you have selected a deforming domain in the moving mesh interface (or I guess 2 in tour case, since I understand you have a small droplet inside a bigger volume, in such case you need to use the Fluid/Fluid Interface).

You should not be using the Marangoni multiphysics though, which is not meant to be used with moving mesh. Just having a surface tension that depends analitically on the temperature should be enough. You may add the dependance on the concentration for the surface tension if you know the dependance and if that makes sense in your case.

Originally Posted by Lorenzo210

Hi everyone,


I am using COMSOL 6.1 to simulate a droplet evaporation.


Geometry:
- 2D axis symmetric domain, 90degrees circle domain with R= 60*R_droplet
- Droplet initialized with its R_droplet and theta0 contact angle.


Physics:
- Laminar two phase flow with moving mesh;

- Heat tranfer in fluids;
- Transport of concentrated species;
- Transport of diluited species;

- Mathematical ODE for various calculations.


Multiphysics:
- Nonisothermal flow
- Marangoni effect
-Reacting flow


Problem: I tried to apply the Marangoni effect to the liquid-gas interface, but I cannot select the interface, only wall boundaries can be selected.


I am a bit confused because I took an identical model written in COMSOL 5.6 (not sure about the version), and the Marangoni effect can be applied to the interface.


The 5.6 Marangoni effect gives a warning that "This feature is obsolete and will be removed in future versions." so for that reason I am trying to use the new Marangoni effect version.


Has anyone any clue why the newest version cannot select the liquid-gas interface? The tutorial and the COMSOL documentation (user guide and similar) have not helped.


I was able to run successfully the older model enabling and disabling the Marangoni Effect, so the only issue is with the newest version.


Many thanks.


Regards,
Lorenzo

[Lorenzo210]

Originally Posted by Feeric

You should be able to select your interface thanks to the Free Surface boundary condition that appears in the laminar flow physics, provided that you have selected a deforming domain in the moving mesh interface (or I guess 2 in tour case, since I understand you have a small droplet inside a bigger volume, in such case you need to use the Fluid/Fluid Interface).

You should not be using the Marangoni multiphysics though, which is not meant to be used with moving mesh. Just having a surface tension that depends analitically on the temperature should be enough. You may add the dependance on the concentration for the surface tension if you know the dependance and if that makes sense in your case.

Hello Feeric,


Thank you very much for the suggestion!
I didn't know that the Marangoni multiphysics is not meant to be used with moving mesh, may you kindly tell me where I can find (or understand) that type of information?



Yes, I have a droplet inside a domain and I'm using a moving mesh, so the analytical implementation you suggested seems to work.


I was confused because I tried implementing the multiphysics in many versions (available from the COMSOL's test case tutorial for Marangoni effect), and the 5.6 version allows me to use the multiphysics on the liquid-liquid interface.


Best regards,
Lorenzo

[Mitra2440]

Hi there,

I am modeling the melting process and facing the same issue as you. I was wondering how you managed to solve it. Could you please share the details?

[Lorenzo210]

Hi Mitra,


If the issue is the same (not being able to use multiphysics coupling "Marangoni effect"), I did as Feeric suggested: I used laminar flow/fluid-fluid interface to detect the interface between two phases; here, you can include a User defined surface tension coefficient, which I called sigma.


The value of this variable (sigma) is calculated via an expression dependent on T (thermal Marangoni).


Hope this might be helping, if not please describe a bit more in detail what the problem is in your simulations.


Regards,
Lorenzo

[Mitra2440]

Thanks for your response.

I am modeling the melting process, where a rectangular domain represents the air environment, and the curved section consists of powder particles that should melt when heated by the laser. I am using the phase field method along with laminar flow and heat transfer. The powder is considered a PCM, behaving as a highly viscous fluid in its solid phase.

I also need to account for the Marangoni effect. However, when I add it through the multiphysics option, I am unable to select the appropriate interface. When I try the method you recommended, I still cannot choose the interface. To work around this, I added the moving mesh physics, which allows me to select the intended boundary, but the solution fails to converge.

I am unsure whether the combination of moving mesh, phase field, and the applied Marangoni effect is fully compatible. Do you have any recommendations on how to approach this issue?

Originally Posted by Lorenzo210

Hi Mitra,


If the issue is the same (not being able to use multiphysics coupling "Marangoni effect"), I did as Feeric suggested: I used laminar flow/fluid-fluid interface to detect the interface between two phases; here, you can include a User defined surface tension coefficient, which I called sigma.


The value of this variable (sigma) is calculated via an expression dependent on T (thermal Marangoni).


Hope this might be helping, if not please describe a bit more in detail what the problem is in your simulations.


Regards,
Lorenzo

[Lorenzo210]

Hi,


All right, so I am using a different approach (ALE) to model two-phase flow, where I set all the conditions in laminar flow, because each mesh region I define is treated as separated.


In the case with phase field, I think you are not supposed to use laminar flow to set the conditions in the solid/liquid interface, because the distinct phases are evaluated every time step by the Phase field physics.



Instead, you might set the surface tension coefficient in Multiphysics/ Two-Phase Flow, Phase field 1 (tpf1): here, after "advanced settings" you can set the option to "include surface tension force in momentum equation".


Instead of using a library coefficient, you can choose a user defined coefficient, which you can preemptively create in component1/"Defintions" (for example) using a temperature dependent correlation.


I am not really confident with Phase field or Level set in COMSOL so I can't tell more than that. As an example, in tpf1 there's also the option of "include surface tension gradient effects in surface tension force", which really looks like Marangoni effect, but I am not sure the difference in turning that off or on. It might be useful to look at "Equation" on top and see what changes.


PS: A bit off topic: I would be actually interested in using phase-field, but I am struggling in finding a way to couple it with chemical transport of species, which is needed for my simulations... if you have any hint on how to couple them I would appreciate it!



Regards,
Lorenzo

[Mitra2440]

Dear Lorenzo,

Thank you very much for your help. I tried the approach you recommended, but I still encountered some convergence issues. However, I have now realized which part I should focus on.

I am not familiar with chemical transport, but my model also requires a section for mass addition, which I have no idea how to handle. Until now, I have mainly been struggling with the Marangoni effect and tracking the melt pool surface.

Take care,
Mitra

Originally Posted by Lorenzo210

Hi,


All right, so I am using a different approach (ALE) to model two-phase flow, where I set all the conditions in laminar flow, because each mesh region I define is treated as separated.


In the case with phase field, I think you are not supposed to use laminar flow to set the conditions in the solid/liquid interface, because the distinct phases are evaluated every time step by the Phase field physics.



Instead, you might set the surface tension coefficient in Multiphysics/ Two-Phase Flow, Phase field 1 (tpf1): here, after "advanced settings" you can set the option to "include surface tension force in momentum equation".


Instead of using a library coefficient, you can choose a user defined coefficient, which you can preemptively create in component1/"Defintions" (for example) using a temperature dependent correlation.


I am not really confident with Phase field or Level set in COMSOL so I can't tell more than that. As an example, in tpf1 there's also the option of "include surface tension gradient effects in surface tension force", which really looks like Marangoni effect, but I am not sure the difference in turning that off or on. It might be useful to look at "Equation" on top and see what changes.


PS: A bit off topic: I would be actually interested in using phase-field, but I am struggling in finding a way to couple it with chemical transport of species, which is needed for my simulations... if you have any hint on how to couple them I would appreciate it!



Regards,
Lorenzo