This work aims at studying in-line bubble coalescence in non-Newtonian
fluids. The visualisation and power spectrum of time series data, rec
orded via an optical sensing device, confirm that the bubble formation
at the orifice is perfectly periodic under a constant gas flowrate. H
owever, the separation interval between bubbles becomes irregular duri
ng rise, until, at a certain height above the orifice, the coalescence
occurs. An original approach is elaborated by relating the rise of a
chain of bubbles to consecutive shear deformations. A series of measur
ements on a rheometer proves for the first time that the bubble coales
cence is mainly governed by the dynamical competition between the crea
tion and relaxation of shear stresses. The time delay embedding method
of reconstructing the phase-space diagram is applied to time series d
ata recorded at different heights in the bubble column. The calculatio
n of several parameters: the largest Lyapunov exponent, the correlatio
n dimension, the power spectrum, and the phase portraits, reveals that
the coalescence between bubbles obeys a chaotic and deterministic mec
hanism. (C) 1997 Elsevier Science Ltd.