Study of Bubble Size, Void Fraction, and Mass Transport in a Bubble Column under High Amplitude Vibration

Shahrouz Mohagheghian,Afshin Ghajar,Adam Still,Brian Elbing

doi:10.3390/chemengineering2020016

Shahrouz Mohagheghian, Afshin Ghajar + Show 2 more

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https://doi.org/10.3390/chemengineering2020016

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Abstract

Vertical vibration is known to cause bubble breakup, clustering and retardation in gas-liquid systems. In a bubble column, vibration increases the mass transfer ratio by increasing the residence time and phase interfacial area through introducing kinetic buoyancy force (Bjerknes effect) and bubble breakup. Previous studies have explored the effect of vibration frequency (f), but minimal effort has focused on the effect of amplitude (A) on mass transfer intensification. Thus, the current work experimentally examines bubble size, void fraction, and mass transfer in a bubble column under relatively high amplitude vibration (1.5 mm < A <9.5 mm) over a frequency range of 7.5–22.5 Hz. Results of the present work were compared with past studies. The maximum stable bubble size under vibration was scaled using Hinze theory for breakage. Results of this work indicate that vibration frequency exhibits local maxima in both mass transfer and void fraction. Moreover, an optimum amplitude that is independent of vibration frequency was found for mass transfer enhancements. Finally, this work suggests physics-based models to predict void fraction and mass transfer in a vibrating bubble column.

Highlights

Bubble columns are used in many applications including aeration of organic organisms in bioreactors, indirect liquefaction of coal-slurries to produce synthetic fuels via Fischer-Tropsch process and gasification of solvent for chemical reactions
Budzynski et al [22] recommend H > 8D to minimize the impact of the liquid surface deformation on void fraction measurements
The first set was conducted to validate the experimental setup against published research data, and the second to investigate the effects of large amplitude vibration

Summary

Introduction

Bubble columns are used in many applications including aeration of organic organisms in bioreactors, indirect liquefaction of coal-slurries to produce synthetic fuels via Fischer-Tropsch process and gasification of solvent for chemical reactions. There has been a renewed interest in the study of vibrating bubble columns [12,13,14,15,16,17,18,19,20,21,22] These recent efforts have developed theoretical physics-based models to predict mass transfer and void fraction in bubble column reactor (BCR) systems undergoing vibration [18,19,20]. These models were tested in a limited range of data, but have yet to be fully understood or validated against a broad range of experimental data. The current work aims to expand the available parameter space and test current models

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