EVIDENCE FOR IN-LINE BUBBLE INTERACTIONS IN NON-NEWTONIAN FLUIDS

This work reports a study of in-line bubble interactions in non-Newton ian fluids by varying the injection period between bubbles. The experi mental data reveal that the bubble rise velocity depends upon the inje ction period, obviously due to in-line interactions. The original rheo logical simulation, based on the close relationship between the rise o f a chain of bubbles and consecutive shear deformations, proves for th e first time that in-line interactions are mainly governed by a dynami cal competition between the creation and relaxation of stresses in flu ids. This interaction mechanism is clearly corroborated by a newly dev eloped visualisation method based on birefringence. With the decrease of the injection period, such interactions become strong enough and co alescence occurs. The spectral analysis of the bubble passage at diffe rent heights in the column demonstrates that the interactions are no l onger linear accompanied by successive bifurcations leading to chaotic coalescence. (C) 1998 Elsevier Science Ltd. All rights reserved.