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