Drop breakup laminar flow

FIGURE 11.7 Two types of laminar flow, and the effect on deformation and breakup of drops at increasing velocity gradient ( ). The flow is two-dimensional, i.e., it does not vary in the z-dircction. More precisely, the flow type in (b) is plane hyperbolic flow. ... 

FIGURE 11.8 The effect of the viscosity ratio, drop over continuous phase inn/tlc), on the critical Weber number for drop breakup in various types of laminar flow. The parameter a is a measure of the amount of elongation occurring in the flow for a — 0, the flow is simple shear for a — 1, it is purely (plane) hyperbolic. 

Breakup of Single Drops in Laminar and Turbulent Flow. The... 

Breakup Mechanism and Daughter Drop Production in Laminar Flow... 

It is not our purpose to provide a complete discussion of drop deformation and breakup in idealized laminar flow fields. There have been numerous studies that have been reviewed by Rallison (1984), Stone (1994), and others. Only the most practically relevant studies are discussed below. Of central importance is to predict and/or correlate the size above which a parent drop of known physical properties (that is subjected to an imposed deformation) will become unstable and break up into smaller drops. This size is referred to as the critical or maximum stable drop size, dmax-... 

Atomization. A gas or Hquid may be dispersed into another Hquid by the action of shearing or turbulent impact forces that are present in the flow field. The steady-state drop si2e represents a balance between the fluid forces tending to dismpt the drop and the forces of interfacial tension tending to oppose distortion and breakup. When the flow field is laminar the abiHty to disperse is strongly affected by the ratio of viscosities of the two phases. Dispersion, in the sense of droplet formation, does not occur when the viscosity of the dispersed phase significantly exceeds that of the dispersing medium (13). 

From the above the maximum stable drop size can be estimated. There will be smaller drops, but in theory no drops larger than this. No data on distribution as yet exist for laminar breakup. Figure 7-28 compares drop size by laminar mechanisms with those calculated for turbulent flow. Smaller droplets are expected for laminar versus turbulent flow at the same energy dissipation rate. 

Simple laminar shear or extension flow produces orderly dispersion since the flow field surrounding the drop is constant and continuous. In contrasL simple turbulent flows produce more random breakup events, due to the time-dependent nature of fluid-drop interactions. The effect of breakage mechanism on the resulting DSD is sometimes counterintuitive. 

From an analytical viewpoint, the flow fields in laminar devices are highly dependent on geometry, and individual drops experience varied deformation paths of long time scale that are difficult to analyze. Even if Lagrangian tracking of deformation and breakup history of many drops were possible, it would be difficult to apply this information to real-life systems. Therefore, most studies... 

Until now, the effect is not explicitly described in literature. Based on experiences during spray experiments with the LamRot, the question of whether the cross-wind flow leads to an increase in mean drop size and in span value of the drop size distribution has to be answered. In case of confirmation, the results of the similarity trials on the thread breakup in the field of gravity could help to find better design of the gas distributor for a spray drying process with the laminar operating rotary atomizer. The span value of the dried product is the main objective as it is the crucial quality feature of the spray drying process. The optimized process could be applied to produce high qualitative products, e.g. for pharmaceuticals, chemicals, or food materials. 

The results also elucidate the influence of the cross-wind flow on the drop formation from laminar threads in the range of typical process condition for the LamRot. The drop size increases slightly due to the effect of shorter breakup length. The theory of increasing wave number [32] does not fit in case of stretched threads. The relevance of the slight increase below the transition to wind-induced breakup for the design of a spray process with the LamRot is low. 

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