Breakup types

Ca waves in systems [ike Xenopus laevis oocytes and pancreatic (3 cells fall into this category Electrochemical waves in cardiac and nerve tissue have this origin and the appearance and/or breakup of spiral wave patterns in excitable media are believed to be responsible for various types of arrhythmias in the heart [39, 40]. Figure C3.6.9 shows an excitable spiral wave in dog epicardial muscle [41]. 

In many types of contactors, such as stirred tanks, rotary agitated columns, and pulsed columns, mechanical energy is appHed externally in order to reduce the drop si2e far below the values estimated from equations 36 and 37 and thereby increase the rate of mass transfer. The theory of local isotropic turbulence can be appHed to the breakup of a large drop into smaller ones (66), resulting in an expression of the form... 

Internal Flow. Depending on the atomizer type and operating conditions, the internal fluid flow can involve compHcated phenomena such as flow separation, boundary layer growth, cavitation, turbulence, vortex formation, and two-phase flow. The internal flow regime is often considered one of the most important stages of Hquid a tomiza tion because it determines the initial Hquid disturbances and conditions that affect the subsequent Hquid breakup and droplet dispersion. 

Droplet breakup via impingement appears to follow a similar relationship, but much less data is available. This type of breakup can result from impingement on equipment walls or compressor blades. In general, there is less tendency to shatter on wetted surfaces. 

Another type of crossflow cooling tower is the wet-dry tower, which consists of a normal crossflow tower over which a few air coils are placed. The hot water is first cooled by an air cooled heat exchanger and then drops to the wet cooling tower where more cooling is obtained by the evaporative mechanism. Figures 5 and 6 provide examples. In contrast, deck-filled towers contain tiers of splash bars or decks to aid in the breakup of water drops to increase the total water surface and, subsequently, the evaporation rate. 

Mechanical compatibilization is accomplished by reducing the size of the dispersed phase. The latter is determined by the balance between drop breakup and coalescence process, which in turn is governed by the type and severity of the stress, interfacial tension between the two phases, and the rheological characteristics of the components [9]. The need to reduce potential energy initiates the agglomeration process, which is less severe if the interfacial tension is small. Addition... 

Illustration Common flow types. Experimental studies of drop breakup have been mainly confined to linear, planar flows. All linear flows in 2D are encapsulated by the general velocity field equations... 

There have been several attempts at models incorporating breakup and coalescence. Two concepts underlie many of these models binary breakup and a flow subdivision into weak and strong flows. These ideas were first used by Manas-Zloczower, Nir, and Tadmor (1982,1984) in modeling the dispersion of carbon black in an elastomer in a Banbury internal mixer. A similar approach was taken by Janssen and Meijer (1995) to model blending of two polymers in an extruder. In this case the extruder was divided into two types of zones, strong and weak. The strong zones correspond to regions... 

Other reverse-bias annealing experiments have been published that can be analyzed in the same way. Tavendale et al. (1985) used 10 ft cm boron-doped silicon passivated by exposure to plasmas containing or 2H. Schottky diodes formed with such specimens showed breakup of BH under heating at 80°C with reverse bias however, there was a persistence of passivation in the first two or three microns that must be attributed to some sort of near-surface reservoir of hydrogen. This effect was absent in an annealing experiment on a junction diode with an -type surface... 

Much of the discussion of this subsection has been based on the behavior of hydrogenated diodes annealed under reverse bias. Annealing under forward bias has also been studied, though less extensively, and some of the observations have suggested the possibility of a new type of thermal breakup of BH complexes, namely BH + e— B + H° (Tavendale et al., 1985, 1986a). These authors reported breakup of BH in a few hours at 300 K under forward bias, both in Schottky diodes and in n+-p junctions. However, in a similar experiment with an n+-p junction, Johnson (1986) found a slight buildup of BH under forward-bias anneal. Available details of the various experiments are too sketchy to allow useful speculation on the reasons for the different outcomes or possible mechanisms for accelerated breakup. 

Normal Pulsating Axisymmetric Rayleigh-type Sheet forms a round jet No breakup WfN <15... 

Figure 33. (a) Axisymmetric and (b) Non-axisymmetric Rayleigh-type breakup mode of round liquid jets in coaxial air flow. (Reprinted with permission from Ref. 210.)... 

Figure 3.5. Fiber-type breakup mode of round liquid jets in coaxial air flow.

Farago and Chigier 2l() found that at similar aerodynamic Weber numbers, the disintegration modes of a thin liquid sheet in air streams are similar to those of a round liquid jet in a coaxial air stream (Table 3.2). At high aerodynamic Weber numbers, Membrane-Type or Fiber-Type breakup mode may set in. 

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