haveD¼We. For larger values of We, the drop is further deformed as
depicted, and it breaks if We>Wecr. Values of Wecrare given in Figure
11.8, curve fora¼0. Inserting the value of Wecrin Eq. (11.5) yields fordthe
value of the largest drop size that can remain unbroken in the flow field
applied. The average drop size resulting would be somewhat smaller. Table
11.2 gives the equation ford.
It is seen that theviscosity ratioZD=ZChas a large effect on Wecrin
simple shear flow, i.e., on the viscous stress needed to break up a drop of a
FIGURE11.8 The effect of the viscosity ratio, drop over continuous phase
ðZD=ZCÞ, on the critical Weber number for drop breakup in various types of laminar
flow. The parameterais a measure of the amount of elongation occurring in the
flow: fora¼0, the flow is simple shear; fora¼1, it is purely (plane) hyperbolic.