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-   -   Changing contact line (http://www.cfd-online.com/Forums/flow-3d/70630-changing-contact-line.html)

tfe December 1, 2009 02:44

Changing contact line
 
Hello,

If you simulate the evaporation of a water droplet on a substrate the contact line stays the same while the volume is decreasing. I would like to model the evaporation of a water droplet on a substrate with a changing contact line between water and substrate. Is there an option within flow 3D to get a closer look into the behaviour of the droplet while the contact line is changing? I mean is there a simulation option to model a changing contact line?

Best Regards,

Leo

MuxaB December 2, 2009 00:30

Leo,

I would think the contact line would move as the volume decreases, maintaining a constant contact angle. In any case, there is no option to pin the contact line in FLOW-3D.

Michael

tfe December 3, 2009 16:29

Hello Mike,

Thanks for your reaction. I am wondering whether it is possible to model a changing contact line because I would like to use the changing contact line for a residue model which is activated by iresid. In the FLOW 3D technical note 80 “Simulating the Residue left by Evaporation” on page 2 something is written about the possibility to pin the contact line.
On page 2 and page 3 the paper says: “A different technique was then used that worked quite well. This consisted of the use of a phantom obstacle surrounding the initial drop and extending vertically upward to the top of the grid, forming a cylindrical wall around the droplet, with the radius equal to the initial droplet radius. Within the phantom component the permittivity is zero so that fluid cannot penetrate the space occupied by it, however, as with any phantom components, there are no area or volume blockages. Because it has no solid surfaces the phantom obstacle does not alter the surface-tension wall adhesion forces. With this component in place the contact angle for the fluid is set to a low (wetting) value, e.g. 0.0. Effectively the low contact angle makes the fluid want to move outward, but it is restrained by the phantom obstacle’s zero permittivity, creating the net effect of a pinned contact line.

Can you explain me how to model this phantom obstacle? Why is no area or volume blockage allowed?
And how can this phantom obstacle be implemented together with the iresid setting?

Best regards,

Leo

tfe December 8, 2009 02:59

Quote:

Originally Posted by mike@flow3d.com (Post 238420)
Leo,

I would think the contact line would move as the volume decreases, maintaining a constant contact angle. In any case, there is no option to pin the contact line in FLOW-3D.

Michael

I understand what you mean, but I thought the contact line changes sometimes for a rough surface. The reason why I thought about this is that I would like to model a residue which is left by evaporation for the case there are some ink particles mixed with the water droplet. This is indicated in FLOW 3D technical note 80 ("Simulating the residue left by evaporation").

Does someone have more information about how to implement these iresid settings? It seems that the IRESID and RMXSC function don't influence the results of the simulations. Because when I use this option no residue is left on the substrate. Are there any other boundary conditions needed? Or could it be because of the phantom obstacle about which is talked about before in this topic?


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