The flow and drainage of foams and films.
The behaviour of gas-liquid foams has been the subject of extensive research in the past
century because of the usefulness of liquid foams in industry. In this work we present
new experimental and theoretical developments concerning flow and drainage behaviour
of surfactant based liquid foams and films.
The flow of free films and foam was studied in vertical tubes for different liquid
properties. Measurements of the thickness of the lubricating layer on the wall and CFD
simulation shows a relationship between the liquid thickness, liquid viscosity and
pressure drop for the flow of free films. For foam flow, friction factors were determined
for all systems and data lied remarkably on a unique line on the friction factor-Reynolds
number plot and has a practical significance in that pressure drop can be calculated using
a constant friction factor along a pipe of a constant cross section in any flow regime.
An improved ER technique has been developed for accurate measurements of
foam resistance, which includes the liquid layer at the wall. Traditional ER-methods for
characterising the drainage of a wall-confined static foams do not take into consideration
the effects of a substantial liquid layer established on the wall during drainage which
transports a substantial amount of liquid. A method is proposed for the estimation of
temporal as well axial variations of the wall liquid thickness inferred from the
measurements of the local liquid holdup. A theoretical model is proposed for foam
drainage based on the analogy of liquid flow through a packed bed of solid particles. A
good agreement is obtained between theory and experiment on the basis of judicious
estimations of foam cell size and shape factor.