Figure 3. Statistical results of DBFF. (a) The DBFF at different
height under mass transfer condition. (b) The DBFF at different height
for the blank experiments without mass transfer.
In above Section, the droplet number density functions at different
height have been obtained. The breakup frequency functions at different
heights of the column can then be determined through the method
described in experiments and methods. The results are shown in Figure
3(a). In turbulent flow field, large droplets receive more energy due to
the collision of more turbulent eddies and are more likely to break up.
Figure 3(a) also shows that the DBFFs for droplets with the same
diameter are different at different heights. The DBFF is the highest at
265 mm and then decreases gradually with the increasing of column
height. In our experiment, the operating conditions of the extraction
column are unchanged, so the turbulent kinetic energy along the column
height should be the same. For droplets of the same size, the frequency
of turbulent eddy collision is also the same. In this scenario, the
breakup frequency changing at different height is mainly caused by the
variation of interfacial tension. In the extraction column, the
concentrations of solute in the two phases change with the column height
while the existence of mass transfer process also causes the instability
of the interface. These two aspects will
ultimately
affect the interfacial tension. The interfacial tension at different
height can then be determined by regression from the measured breakup
frequency. In this way, the DIFT in the pulsed column can be measured.
As a comparison, blank experiments are carried out in order to confirm
that the breakup frequency is not affected by the column height without
mass transfer. Deionized water and 5% (v/v) TBP in kerosene are used as
the dispersed and continuous phase separately. By using the same
statistical method as mass transfer experiments, the DBFFs at different
height are measured. The results are shown in Figure 3(b). We can see
from the figure that the DBFFs at different height are almost the same
in the blank experiments without mass transfer. This result further
proves that the DBFF curves shown in Figure 3(a) have a one - to - one
correspondence with the DIFT in the pulsed column.
Regression of dynamic interfacial
tension