Shear breakup regime

Table 3.3 Values of Weber Number for Transitions from No Deformation Regime up to Shear Breakup Regime at 0hd <0.1...

The DDB model is applicable to the shear breakup regime, assumed to start at... 

F. 29.10 (a) Formation of drops from ligaments formed on the downstream side of the jet in the shear breakup regime (b) schematic top view of the cross section of a nonturbulent Jet at which a droplet (or ligament) is being formed similar to panel (a) (a From Herrmann [12]. Reprinted with permission. Copyright (2010) ASME)... 

Current breakup models need to be extended to encompass the effects of liquid distortion, ligament and membrane formation, and stretching on the atomization process. The effects of nozzle internal flows and shear stresses due to gas viscosity on liquid breakup processes need to be ascertained. Experimental measurements and theoretical analyses are required to explore the mechanisms of breakup of liquid jets and sheets in dense (thick) spray regime. 

Critical capillary numbers for elongational flows are lower than for shear flows. In other words, the elongational flow field is much more effective for droplet breakup in a dispersive mixing regime (Grace 1982). 

Taylor [64] found that in simple shear flow, a dispersed drop with viscosity ratio p = 1 breaks up when the Ca > 0.5. Breakup seems to occur when the shear stress and the interfacial stress are of the same order of magnitude. The critical Capillary number depends on the type of flow and on the viscosity ratio. In the mixing process two regimes can typically be distinguished ... 

Emulsions have been pumped over long distances in laminar flow. Nunez et al. (1996) demonstrates the existence of certain effects similar to comminution, i.e., breakup of large droplets into finer ones, as weU as coalescence of smaU particles into larger ones under different flow regimes, shear rates, and constraints. 

---