Break-up, coalescence and catastrophic phase inversion in turbulent contactors

When a low concentration of immiscible phase is dispersed, break-up in the impeller region controls the drop size. The traditional application of Kolmogoroff's theory of local isotropic turbulence has been moderately successful in relating equilibrium drop sizes to the physical properties and t...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Advances in colloid and interface science 2004-05, Vol.108, p.95-103
1. Verfasser: Nienow, A.W
Format: Artikel
Sprache:eng
Schlagworte:
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung:When a low concentration of immiscible phase is dispersed, break-up in the impeller region controls the drop size. The traditional application of Kolmogoroff's theory of local isotropic turbulence has been moderately successful in relating equilibrium drop sizes to the physical properties and the turbulent flow, with low power number impellers giving smaller drops at equal mean specific energy dissipation rates, ε ̄ T. However, to explain the reduction in drop size at equal ε ̄ T on scale-up, the concept of intermittency must be introduced leading to a scale-up rule close to constant tip speed. With increasing concentration, coalescence generally becomes important and drop sizes increase. Modelling of coalescence involves collision frequency and coalescence efficiency. The latter is dependent on the type of drop interface, the establishment of which type for a particular system being difficult. The difficulty is compounded since in clean systems, at concentrations of the aqueous phase >∼20% by volume, droplets of oil appear in the aqueous drops whilst the converse is not found. At sufficiently high concentrations, where the concept of collision frequency is questionable, catastrophic phase inversion (CPI) occurs because coalescence becomes so high. Anything that enhances coalescence, e.g. surfactants, particles that bridge interfaces, wettable surfaces, bulk flow patterns, encourages CPI to occur at lower concentrations of dispersed phase. Satisfactory models for CPI are not available.
ISSN:0001-8686
1873-3727
DOI:10.1016/j.cis.2003.10.020