The preparation of concentrated aqueous silicone oil emulsions has been investigated
with particular attention to the effect of the dispersed-phase volume fraction ϕ
from 0.01 to 0.5 for a wide range of oil viscosities (50 to 1000 cSt). Oil was
added on the top surface of a 6-L vessel. Drop size distribution and Sauter mean
diameter, d32, measurements were carried out over 24 h mixing time. Emulsification
was found to be relatively sensitive to the oil phase viscosity, ld, for the same
ϕ yielding a narrower drop size distribution for low oil viscosity (50 cSt) and a
wider drop size distribution for the highly viscous oil (1000 cSt). For the same ,
increasing ld resulted in increasing d32. The equilibrium d32 was found to be well
correlated to the viscosity number by
d32
D 0026 V0204
i for = 0.5. For the
same oil viscosity, d32 was found to increase with increasing . A multiregression
of d32 with both and Vi for various silicone oil viscosity grades was successfully
correlated by d32 960069V0216
i with a regression coefficient (R2) of 0.975.
This shows a very weak dependence of the equilibrium d32 on .
Keywords: Dispersed-phase volume fraction, Drop size distribution, Liquid-liquid
dispersion, Silicone oil, Surfactant
Received: January 22, 2009; revised: March 23, 2009; accepted: April 27, 2009
DOI: 10.1002/ceat.200900038
1 Introduction
Liquid–liquid dispersion is one of the most complex of all
mixing operations. Agitating two immiscible liquids results in
the dispersion of one phase in the other in the form of small
droplets with drop size distributions whose characteristics
depend on the equipment and the operating conditions. It is
virtually impossible to make dispersions of uniform drop size,
because of the wide range of properties and flow conditions.
The knowledge of the resulting drop size distribution characteristics
or, more exactly, the evolution of this distribution
with changes of external energy input is of major importance.
A large amount of work can be found in the literature concerning
the prediction of drop size distributions in turbulent
liquid-liquid dispersions in stirred vessels. Most of them use
the concept of a turbulent energy cascade to predict the maximum
stable diameter,