Theoretical analysis of fluid particle collisions in turbulent flow

Bubble and drop coalescence phenomena observed in many industrial separatio n processes and in multiphase chemical reactors such as bubble columns and stirred vessels, often have a significant influence on the process performa nce. Even though a number of sophisticated modelling concepts have been pre sented in the literature over the years, the chemical and physical mechanis ms involved are still not satisfactorily understood. Among the most promisi ng methods applicable for elucidating these phenomena are the 'volume of fl uid (VOF)' and the direct numerical simulation (DNS) methods. On the other hand, the multifluid models have been found to represent a trade-off betwee n accuracy and computational efforts for practical applications. In these m ultifluid models constitutive equations are needed to describe the coalesci ng process, and due to the limited understanding of these phenomena we stil l have to resort to empirical correlations. The present model belongs to th e latter class and deals with the collision process between two fluid parti cles. The intention is to formulate a constitutive model that can be applie d for determining whether the particles coalesce or not. The model should b e applicable for both phenomenological reactor models and CFD-based reactor models. Turbulence is included by using collision time scales generally le ss than a second, and by including fluid particle shape oscillations. (C) 1 999 Elsevier Science Ltd. All rights reserved.