CFD Simulation and Analysis of Micro Bubble Generating Nozzles for Microreactors

Abstract:
Monodisperse micro bubbles (radius ca. 50 µm) are a great benefit for direct fluorination of liquid aromatics. The fluorination process is improved by the large gas-liquid interface compared to slug or jet flow. In this paper we describe a new nozzle concept for monodisperse micro bubble generation which enables a variation of bubble size due to its geometry. The nozzle is a microchannel which is perpendicular to the liquid channel. Snap-off mechanism was described by a measured pressure history inside the nozzle channel. This allows to analyze the size and frequency of bubble generation and therefore, the size of the gas-liquid interface. Quadratic and rectangular geometries were designed and simulated in a three dimensional multiphase system to calculate the formation of fluorine bubbles in toluene. The influence of aspect ratio on the bubble size, generation frequency and liquid flow are presented. It is shown that a rectangular geometry has the fastest snap-off with the smallest bubbles.