An-Najah Staff

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
0
026  V0
204 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
9
6
0
069V0
216 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,