Laboratory experiments (12):
Foam shape at steady-state:
1) Maximum height: Hm
Hm = f(Q,m)
2) Critical height above which the foam starts to coalesce: Hc
Buoyancy > surface tension, s
Unstable foam
Hc
=
4 s
r g
d e
Hm > Hc
Foam coalescence
Gas jet = fire fountain
Q: gas flux; m:viscosity; d: bubble diameter
:gas volume fraction
in foam;
:magma density; g: acceleration of
gravity