SURFACE PHENOMENA IN LIQUID-LIQUID DISPERSIONS .2. THE EFFECT OF DISPERSED PHASE HOLDUP ON DROP SIZE

The latest literature data on liquid-liquid dispersion in mixers indicate that d32 does not depend only on hydrodynamic forces and individual component properties of liquid-liquid systems. Due to interaction of component properties their effect on d32 is more complex than results from most of the correlations. The experimental investigations on the influence of phase inversion on d32 reported in Part I indicate further difficulties of the relationship between d32 and phi and the postulated mechanism of the phenomenon assumes the creation of some new properties as a result of the intensive phase contact in the mixers. The objective of this study is to explain the above mechanism, and the investigation of the effect of phi on d32 during phase inversion seems to be of primary concern. At lower values of dispersed phase holdup (phi less-than-or-equal-to 0,005) the dominant factors responsible for drop size are hydrodynamic forces and phase properties. As a result, physical models for liquid dispersion can satisfactorily predict drop sizes for this range of phi values. At higher values of phi drops in the water phase are considerably larger than those predicted by correlations, and the discrepancy between experimental and calculated values of d32 in the water phase can be as large as 400%. It has been found that hydrodynamic conditions, i.e. impeller speed and the presence of baffles do not affect the relationship between d32 and phi in a qualitative manner. Phase inversion is much more important particularly at higher phi values. This, together with essential changes in the drop size after phase inversion, can indicate an increase of surface phenomenon contribution or even development of new surface properties affecting the equilibrium drop size during intensively proceeding coalescence and dispersion processes at higher values of phi.