The prediction of mass transfer rates to and from moving drops has traditio
nally used the Whitman two-film theory approach in which the resistances to
mass transfer on each side of the interface are described by film mass tra
nsfer coefficients. These are correlated in terms of the hydrodynamic condi
tions, the physical properties of the fluids, and the geometry of the syste
m. The performance of liquid-liquid contactors in which mass transfer occur
s between swarms of moving droplets of one phase and the other liquid phase
as the continuous phase, has similarly been correlated in terms of mass tr
ansfer coefficients. These lump together the combined effects of interfacia
l mass transfer resistances and those associated with the bulk phases, the
effects of interfacial disturbances, coalescence and break-up phenomena, sp
ecific surface area, and the effects of axial mixing. In this paper we buil
d upon earlier work and other published research which uses finite element
methods to quantitatively calculate flow field data and trajectory predicti
ons for single particles and drops in a two phase system. The differential
equations were discretised using the finite element approach employing a pr
ocedure based on the Lagrangian framework developed earlier. Here we extend
the approach to calculate mass transfer rates between single aqueous drops
and a continuous immiscible solvent phase. The calculated values of drop v
elocity and mass transfer rates are compared with experimental values deter
mined for single drops of ethanol/water mixtures extracting into a continuo
us phase of n-decanol. Good agreement between the experimental and predicte
d values was obtained, thus demonstrating that in this case, interfacial ma
ss transfer in liquid-liquid systems can be predicted from the fundamental
transport equations. The results of the work indicate the potential of furt
her development of this approach for swarming drops and hence quantitative
prediction of the behaviour of liquid-liquid contactors. (C) 2001 Elsevier
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