RÉSUMÉ

There are evidences of complexity that may play a crucial role in flow regime transition of bubbly flow in vertical pipes of centimeter scale. Such a complex nature most likely contributes to several unresolved questions about transient conditions Even much less is known about bubbly flow in complex geometry that is designed for special applications. The reason is two fold, first because there are a vast number of possible apparatuses that utilize bubbly flow. Second, the initial and boundary conditions may alter the appearance of dispersed structure so that there seems to be no common first principles applicable to several cases. Different examples were undertaken in these studies to prove that this may not be so. They are: bubbly to slug flow transition in a vertical pipe under adiabatic conditions, cavitating bubbly structures and suspended bubbles in forced mixing. Although different cases by nature, they enable a common approach that can be described roughly as a two-part process: first, the scale information is broken into parts, and once the information is analyzed by the discrimination system lower level, it can be reassembled by the system higher level to tell us what is where in the environment. The following features of complexity are pointed out: significant interaction, high number of parts or degrees of freedom, nonlinearity, broken symmetry, and nonholonomic constraints. It is shown in this paper how these principles of complexity can eventually explain a controversial behavior on macroscale by identifying key phenomena that are rooted in microscale.