Surface tension and multiple fluids
Jayhawk
with SPH in
http://www.matthiasmueller.info/publications/sca05.pdf
A demonstration video of a lava lamp is shown in
http://www.matthiasmueller.info/videos/lava.avi
The method lets certain effects be generated. For example a lava lamp
is simulated.
It is not accurate though. When two blobs of "lava" meet, they
immediately merge and become one larger deform blob which is then
pulled together in more compact form by surface tension.
A real lave lamp will often show two blobs of "lava" meet and the
bounce off of each other, as if they are made of different material
which will not bond. If sufficient force pushes them together, then
they will give up on their resistance and merge as shown in Mullers
method.
The smaller the blobs, the less likely they are to bounce rather than
merge. If the flask is shaken so the "lava" forms a number of tiny
blobs, then those blobs will not merge with anything untill the lamp
is turned off and the "lava" solidifies on the bottom again.
The question is now, what is the physical effect that prevents two
blobs from merging as soon as they make contact, and how would one
moddel this effect?
I might add that I once saw a demonstrational video which showed
dropplets of water faling into a cup of water, from a low altitude.
The droplets always impacted the surface of the water in the cup and
then bounced back up without merging. Eventually the droplet settled
on the surface of the water and then merged so rappidly that a smaller
droplet was reppeled upwards.
The explanation was that when the drop impacted the surface, there was
a small cushion of air which prevented contact. This took a certain
amount of time to drain, and only after it had drained would water
make contact and merge. Before this happened, the droplet had already
bounced back up again, at a slightly lower altitude than before. The
bouncing kept on until the droplet rested on the surface, air drained
and contact was made.
The same mechanism could be at work in the lava lamp, but then why
does smaller blobs find it harder to merge and how can larger blobs be
pushed hard into each other for up to a few seconds without draining
the layer in between and merging?
Maciej Marek
> The same mechanism could be at work in the lava lamp, but then why
> does smaller blobs find it harder to merge and how can larger blobs be
> pushed hard into each other for up to a few seconds without draining
> the layer in between and merging?
Probably this is a matter of momentum. Smaller blobs have low
momentum so it's harder for them to push away the layer in
between.
Best regards,
Maciej Marek
Olin Perry Norton
[snip]
> The explanation was that when the drop impacted the surface, there was
> a small cushion of air which prevented contact.
>
[snip]
In lubrication this is known as a "squeeze film".
Olin Perry Norton
jfh
Another possibility is that if the interfaces have any surfactant on
them, coalescence is impeded.
John Harper