Learning Forum

[ursen]

Hi!

My problem is referring to a droplet in capillary tube.

The initial contact angle at all contact surfaces is 120°. (as shown in the picture)

[Rob]

As the interface is moving something is happening. What did you set surface tension as? Also check you are solving for surface tension. There was a change in the model so you may have missed the option, it's in the VOF panel 2-3 tab. n

[ursen]

I set surface tension as 0,072 N/m in the Models - Phase Interaction - Surface Tension. It's set as constant - as it should be. n

[Rob]

And the Global Options?n

[ursen]

yes. the samen

[ursen]

I ever tried with option of moving wall (boundary condition - wall adhesion). I tried moving wall in the x direction with speed 0 m/s. nDroplet simply doesn't move. .. n

[ursen]

Is there anything else i sould do in order to move the droplet by defining change in contact angle?n

[Rob]

Assuming you have enough mesh, and wall adhesion & surface tension set the droplet will (should) move based on the local forces. Try increasing the time step in case you've set it so low that the solver doesn't pick up any motion. Remember that droplets can also get stuck in systems as the forces aren't sufficient to move them:try increasing the surface tension to see what happens. n

[ursen]

Rob thank you for all your suggestions.nI've tried increasing time step but with smaller time step droplet starts to evaporate. nI could try to increasing the surface tension but i need my calculation to invole water, because of analitical comparison. nTo sum up - I have 3 surfaces (upper electrode, lower left and lower right electrode). On all of them I have defined a contact angle 60? except for lower right where i defined UDF for a change. I don't have an inlet or outlet - should I define that? Is it possible that there is a pressure problem? n n

[Rob]

If there's no boundary you may find the back pressure causes some issues, set a pressure boundary and see what happens. Also try fixing the lower right contact angle to see what that does. n