Gekoppeltes Berechnen von Blasengrößenverteilungen und Strömungsfeldern in Blasensäulen

Coupled Calculation of Bubble Size Distribution and Flow Fields in Bubble Columns In this paper the use of computational fluid dynamics (CFD) for the calculation of flow fields in bubble columns is explained. The local bubble size distribution is considered with the aid of a simplified balance equation for the average bubble volume in bubbly flow. Models are developed for the rate of bubble break‐up and coalescence based on physical principals. The flow fields in cylindrical bubble columns without internals are calculated using the Euler‐Euler method. The small and large bubble fraction are considered as pseudo‐continuous phases in addition to the liquid phase. The calculated flow fields are characterised by several large scale vortices. The local volume fractions of gas and liquid are very inhomogeneous and highly time dependent. The calculated volume fractions, velocities and bubble size distributions agree well with experimental results for bubble columns up to 0.3 m in diameter.     

Vergleich des Koaleszenzverhaltens ruhender und umströmter Wasser‐in‐Öl‐in‐Wasser‐Einzeltropfen

Phase inversion of a water‐in‐oil emulsion to a water‐in‐oil‐in‐water double emulsion is practically used for liquid/liquid separation. For successful separation in the water leg the coalescence of the internal droplets with the surrounding continuous water phase is decisive. The determination of this coalescence phenomenon is applied for the process design. Therefore, single water‐in‐oil‐in‐water drops are investigated under static and dynamic conditions by means of high speed imaging. The influence of physical and geometrical parameters on the coalescence time and partial coalescence is determined.