2019 EJRNL PP GIORGIO BESAGNI 1.pdf5?
Terbatas Suharsiyah
» ITB
Terbatas Suharsiyah
» ITB
A precise prediction of the fluid dynamics in bubble columns is of fundamental importance to correctly
design “industrial-scale” reactors. It is known that the fluid dynamics in bubble columns is related to the
prevailing bubble size distribution existing in the systems. In this respect, multiphase computational
fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size
distributions and, thus, the global fluid dynamics from the fluid flow conditions and by applying
modeling closured. In particular, in in “industrial-scale” reactors, owing to the large gas sparger openings,
the “pseudo-homogeneous” flow regimedcharacterized by a wide spectrum of bubble sizesdis typically
observed. Unfortunately, reliable predictions of the “pseudo-homogeneous” flow regime are limited up
to now: one important drawback concerns the selection of appropriate models for the coalescence and
break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that
represents the best available knowledge. Recently, the authors have extended the validation of this set of
closure relations to the “pseudo-homogeneous” flow regime, by comparing the numerical predictions to a
comprehensive experimental dataset (gas holdup, bubble size distributions and local flow measurements). Unfortunately, the previous study suffers from some limitations; in particular, in the previous
experimental dataset, the bubble size distributions concerned only one axial position and a detailed
characterization of the gas sparger was missing. This study contributes to the existing discussion and
proposed a step ahead in the study of the “pseudo-homogenous” flow regime. To this end, we propose an
experimental study, to improve the comprehensive dataset previously obtained. The novel datasetdobtained for two gas velocitiesdconcerns bubble size distributions at different axial and radial
positions and a precise characterization of the gas sparger. The comprehensive bubble size distribution
dataset may serve as basis to improve the coalescence and break-up closures; conversely, the precise
characterization of the gas sparger served as an improved input to the numerical simulations. The numerical results, with two different lift force implementations, have been compared with the whole
dataset and have been critically analyzed. Reasons for the discrepancies between the numerical results
and the experimental data have been identified and may serve as basis for future studies