
66 Foam Fractionation: Principles and Process Design
Thus, assuming that the surface tension is spatially constant, the surface free
energy per unit volume of the foam is
G
r
31
32
=
(4.3)
Thus, the system can reduce the surface energy in the bulk of the foam by
increases in the Sauter mean bubble radius, and this is achieved by inter-
bubble gas diffusion and, to a lesser extent, liquid lm rupture. However,
lm rupture can be a major destabilizing mechanism on the free surface of
the foam.
4.2 Coarsening due to Inter-Bubble Gas Diffusion
Inter-bubble gas diffusion (also interchangeably known as Ostwald ripen-
ing, by analogy with the mass tran ...