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Liquid-Vapor interface drops very fast
Posted Mar 18, 2016, 2:01 p.m. EDT Fluid & Heat, Geometry, Mesh Version 5.0, Version 5.1 5 Replies
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I have encountered a problem in COMSOL when using the “laminar two-phase flow, moving mesh” physic.
A simple model indicating what I am trying to solve is provided in the attachment.
As you can see in the attached file, the liquid evaporates at a very low pressure (300 Pa) with a uniform mass flux of 1e-3 (kg/m2s). When the contact angle is 90, everything goes well. However, as I change the contact angle even a little bit from 90 (i.e. pi/2.1), the interface drops very fast, which is physically meaningless. I have had this problem with both COMSOL 4.3b and 5.1.
I could have been able to improve it by making the contact point meshes extremely fine. However, this gives me weird values of pressure (absolute negative pressures) in these regions.
I appreciate if you could help me sort out this issue.
Amin
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Hello Mohammad Amin Kazemi
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I have the same issues with the “laminar two-phase flow, moving mesh” physic in dependence on the contact angle.
Im modelling evaporation of a sessile drop. With “transport of diluted species“ physic the evaporation flux is calculated. The deformation of the drop im modelling with the „laminar two flow, moving mesh“ where the mass flux on the fluid-fluid-interface is coupled with the evaporation flux. With a contact angle of 90° the deformation seems okay, but when the contact angle is set bigger the resulsts get physically meaningless like in your simulation.
Did u solve the issue and could give me some advice? Im using COMSOL 5.0 and I wasnt able to open the attached file because it was saved with a later version of COMSOL.
Thanks in advance.
Lars
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The solution is that you should exclude the contact points in the expression for evaporation flux.
In my geometry, since the r-position of the contact point was always fixed, I used this expression for flux:
if(r<5mm,flux,0)
This means that the evaporation flux is imposed on the interface except at r=5 (SLV contact point).
I recommend you contact COMSOL support and ask if they have a better solution.
Let me know if I can be of assistance.
Amin,
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Question:
In the "laminar two-phase flow moving mesh" physic (tpfmm), when I impose a small amount of flux on the interface, it moves much faster than expected. Is it a bug in COMSOL? This happens for curved interfaces when the contact angle (theta) is not 90. For flat interfaces (theta=90), everything is fine.
I have been struggling with this issue for several months. I appreciate if someone can help.
Amin,
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Best regards,
Jeff
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To address a question to the COMSOL support team, contact support@comsol.com . Please note that this service requires that your license be eligible for that service.
Best regards,
Jeff
Jeff
Unfortunately, my license is not eligible for this service. I wish someone could answer.
Thank you anyway.
Amin,