ABSTRACT
Bubble motion is an important problem for mass transfer applications and is encountered in many industrial applications. Recently, Kulkarni and Joshi underlined in their review [1] the importance of the gas bubbles and their rise, due to buoyancy, for various kinds of the gas-liquid reactors. They stated [1] that gas-liquid conBubble and Drop Interfaces © Koninklijke Brill NV, Leiden, 2011
tacting is one of the most important and very common operations in the chemical process industry, petrochemical industry, and mineral processing. In applications such as absorption, distillation, and froth flotation, the interaction of two phases occurs through dispersing the gas into bubbles and their subsequent rise in the liquid pool. The physicochemical properties of the continuous liquid phase (viscosity, surface tension, density, etc.) and the dispersed phase (bubble size, bubble rise velocity, adsorption coverage over the bubble surface, etc.) govern the hydrodynamics as well as flow pattern in the system. In froth flotation the bubble acts as a carrier of the attached grain(s) having density larger than the continuous liquid medium (pulp). Collectors and frothers are two essential types of the reagents added to the flotation pulp [2-4] for modification surface properties of the liquid/solid and liquid/gas interfaces, respectively. Collectors are expected to make grains of the useful components more hydrophobic, by selective adsorption at their surfaces, while frothers should modify properties of the liquid/gas interface to assure higher degree of the gas phase dispersing and formation of a foam layer of definite properties. As a result of the frother addition the bubbles formed are smaller and their rise velocities are lower. Magnitude of the bubble rise velocity is an important factor in the particle-bubble collision and collection probability, i.e. formation of the bubble grain aggregates. Mechanism and kinetics of the three phase contact formation and the bubble attachment was the subject of many studies [5-15], which were described and summarized in the monograph of Nguyen and Schulze [16]. However, there are still a lot of unanswered questions. For example a significant role of air presence at hydrophobic surfaces (nano-bubbles) [17-22] in facilitation of the three phase contact formation was demonstrated only recently [15, 23, 24] — similarly as some data on influence of the bubble kinetic energy (rising velocity) on its bouncing from various interfaces [25].
