Droplet breakup mechanism

Janssen, J. M. H., and Meijer, H. E. H., Droplet breakup mechanisms stepwise equilibrium versus transient dispersion. J. Rheol. 37(4), 597-608 (1993). 

Wieringa, J.A. Dieren, F. van Janssen, J.J.M. Agterof, W.G.M., 1996, Droplet breakup mechanisms during emulsification in colloid mills at high dispersed phase volume fraction, Chemical Engineering Research Design, 74, 554-562. 

A fragmented liquid core is simulated by injecting large drops which break up into smaller and smaller product droplets, until the latter reach a stable condition. The primary breakup, that is, the first drop breakup after injection, is modeled by delaying the initial drop breakup in accordance with experimental correlations. The drop distortion and the breakup criterion are obtained from Taylor s drop oscillator. The properties of the product droplets are derived from principles of population dynamics and are modeled after experimentally observed droplet breakup mechanisms. 

Droplet Breakup—High Turbulence This is the dominant breakup mechanism for many process applications. Breakup results from local variations in turbulent pressure that distort the droplet... 

As described previously, in the atomization sub-model, 232 droplet parcels are injected with a size equal to the nozzle exit diameter. The subsequent breakups of the parcels and the resultant droplets are calculated with a breakup model that assumes that droplet breakup times and sizes are proportional to wave growth rates and wavelengths obtained from the liquid jet stability analysis. Other breakup mechanisms considered in the sub-model include the Kelvin-Helmholtz instability, Rayleigh-Taylor instability, 206 and boundary layer stripping mechanisms. The TAB model 310 is also included for modeling liquid breakup. 

Droplet Breakup—High Turbulence This is the dominant breakup mechanism for many process applications. Breakup results from local variations in turbulent pressure that distort the droplet shape. Hinze [Am. Inst. Chem. Eng.., 1, 289-295 (1953)] applied turbulence theory to obtain the form of Eq. (14-190) and took liquid-liquid data to define the coefficient ... 

Next we examine the breakup mechanism of immiscible droplets in a continuous phase and that of liquid filaments (30). 

A long, stationary droplet or "thread" of one fluid in another can break up into a string of smaller droplets, and this breakup mechanism has been further treated for slowly moving bubbles by Flumerfelt and co-workers (69,70). In tubes, thread breakup produces bubbles whose lengths are on the order of four times the diameter of the unbroken thread. The incorporation of this mechanism into a constricted tube model for dispersion flow in porous media is described in the chapter by Prieditis and Flumerfelt. 

Figure 12 Mechanisms of droplet breakup and atomization (a) vibrational breakup, (b) bag , hat , or parachute breakup, (c) bag and stamen, parachute and stamen, or umbrella breakup, (d) stripping of thin surface liquid layer, (e) wave crest stripping, and (f) catastrophic or explosive stripping.

The value of the power density may greatly vary among sites in the apparatus. Near the tip of a stirrer, e would have a much higher value than further away. It means that the effective volume for droplet disruption is much smaller than the total volume of stirred liquid. This has two consequences. First, part of the mechanical energy is dissipated at a level where it cannot disrupt drops (and is thereby wasted). Second, droplet breakup takes a long time, because... 

Another important application of the front-tracking method is to simulate the drop/bubble formation in flow-focusing devices. Production of mono disperse drops ubbles in microchannels is of fundamental importance for the success of the concept of lab-on-a-chip. It has been shown that flow-focusing can be effectively used for this purpose. Filiz and Muradoglu performed front-tracking simulations in order to understand the physics of the breakup mechanism and effects of the flow parameters on the droplet/ bubble size in the flow-focusing devices [11]. 

Microsuspension and Inverse-microsuspension. In suspension polymerizations, particle formation occurs through a droplet breakup-coalescence mechanism, with the diameter controlled by the temperature, interfacial tension, agitation intensity and conversion. Suspension polymerizations have typically been characterized by an initiator soluble in the monomer phase and particle diameters in the 50-1000 pm range [40]. Smaller particles (0.2-20 pm) have been produced at higher agitation speeds (lower interfadal tensions) [41] and in such cases a prefix micro has been added to the nomenclature (microsuspension) to reflect both the dominant synthesis conditions (suspension) and the nominal particle size (1 micron). Therefore, microsuspension polymerization has historically referred to a subdomain of suspension polymerization occurring at smaller particle sizes. Based on an analogy to this nomenclature, inverse-microsuspension polymerization has been proposed for similar water-in-oil... 

Following the early work by Thorsen et al., focused on the formation of monodisperse aqueous droplets in an organic carrier fluid performed on a microfluidic chip, and then followed by others works, the breakup mechanism responsible of droplet formation was later analyzed by Garstecki et al. ° showing that when is order of 1 the dominant contribution to the dynamics of breakup at low capillary numbers is not dominated by shear stresses, but it is driven by the pressure drop across the emerging droplet. 

This breakup mechanism is similar to that of a jet breakup in still gases. In the presence of a relatively strong crossflow, however, additional instabilities and waves form on the surface of the jet. These instabilities grow larger as the jet deflects and deforms and contribute to the final jet breakup at Xb- We refer to Xb as the column breakup location (CBL). At this location, the jet disintegrates into a number of relatively large droplets, which themselves undergo secondary breakup processes and become smaller as a part of the atomization process. 

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