Thread-breakup mechanism

In addition to this thread breakup mechanism, gas fingers and large bubbles can also experience bubble snap-off when passing through narrow pore constrictions (20,21). Although snap-off phenomena can be quite complex (21-24), the static analysis of Roof (20) indicates that the resulting bubble diameters are at least twice the pore constriction diameter. 

Illustration Satellite formation in capillary breakup. The distribution of drops produced upon disintegration of a thread at rest is a unique function of the viscosity ratio. Tjahjadi et al. (1992) showed through inspection of experiments and numerical simulations that up to 19 satellite drops between the two larger mother drops could be formed. The number of satellite drops decreased as the viscosity ratio was increased. In low-viscosity systems p < 0(0.1)] the breakup mechanism is self-repeating Every pinch-off results in the formation of a rounded surface and a conical one the conical surface then becomes bulbous and a neck forms near the end, which again pinches off and the process repeats (Fig. 21). There is excellent agreement between numerical simulations and the experimental results (Fig. 21). 

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. 

A key factor in the commercialization of surfactant-based mobility control will be the ability to create and control dispersions at distances far from the injection well (TJ ). Capillary snap-off is often considered to be the most important mechanism for dispersion formation, because it is the only mechanism that can form dispersions directly when none are present (39,40). The only alternative to snap-off is either leave-behind, or else injection of a dispersion, followed by adequate rates of thread breakup and division to maintain the injected lamellae. 

The DR mechanism of high-polymer solutions may be similar to that of surfactant solutions with thread-like micelles being replaced by long polymer chains. However, the different MDRAs, limiting mean velocity profile slopes, and different locations of the transverse turbulent intensity peak positions in polymer and surfactant DR solutions suggest that their mechanisms may be different, probably because of the continual breakup and rapid self-reassembly of the micellar microstructures. 

The most efficient mechanism of drop breakup involves its deformation into a fiber followed by the thread disintegration under the influence of capillary forces. Fibrillation occurs in both steady state shear and uniaxial extension. In shear (= rotation + extension) the process is less efficient and limited to low-X region, e.g. X < 2. In irrotatlonal uniaxial extension (in absence of the interphase slip) the phases codeform into threadlike structures. 

Three different types of microsystem have been reported for the emulsification of a polymerizable liquid (Figure 18.1), namely the terrace-like microchannel device, the T-junction microchannel device and the flow focusing device (FFD). The emulsification mechanism, which is similar for these three devices, proceeds from the breakup of a liquid thread into droplets when the phase to be dispersed is sheared by the continuous and immiscible phase. 

Equations (22.7) and (22.8) allow for the quantitative comparison to the completely filled capillary case. As shown in Fig. 22.7, the threads from open channel flow are 25 % shorter in relation to the prediction. The reason obviously is the increased surface due to the standing wave on the threads upon discharge. The same tendency is proposed for simulation at Institute for Mechanical Process Engineering, University of Stuttgart, Germany. The gap between the breakup... 

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