Droplet deformation processes

Table 4.22a. Dimensionless Numbers Used to Describe Droplet Deformation Processes with Simultaneous Heat Transfer and Phase Change (Solidification or Evaporation)...

Numerous 2-D models have been developed to simulate droplet deformation processes during impact on a smooth surface. Most of these models assumed axi symmetric deformation of a spherical or cylindrical droplet. The models may be conveniently divided into two groups, i.e., compressible and incompressible. 

TLCP droplet deformation in processing equipment and fibrillation, and recent advances in the fibrillation techniques. 

The mechanism of droplet deformation can be briefly summarized as follows. The factors affecting the droplet deformation are the viscosity ratio, shear stress, interfacial tension, and droplet particle size. Although elasticity takes an important role for general thermoplastics droplet deformation behavior, it is not known yet how it affects the deformation of TLCP droplet and its relationship with the processing condition. Some of... 

Figure 3.13. Deformation process of a single droplet impinging on a flat surface (Re = 1600, We = 26.7) (a) simulation left), experiment right), and (b) comparison between calculated and measured dimensionless diameter and height ofa flattening droplet. (Photograph Courtesy of Prof. Dr. Jiro Senda at Doshisha University, Japan. Experimental data reprinted with permission from Ref. 334.)...

Figure 3.14. Deformation process of a single droplet impinging on a non-flat surface (Re = 38115, We = 8474, e/D0=0.33, A/D0=2.8). From top to bottom

Chandra and Avedisian 411] studied the collision dynamics of a liquid (n-heptane) droplet on a polished, solid, stainless steel surface, and on a liquid film created by deposition of a preceding droplet using a flash photographic method. They presented a comprehensive series of clear images of droplet shape, morphology, and structure during the deformation process. In their experiments, the... 

Atomization, or generally speaking droplet generation, is an extremely complex process that cannot yet be precisely predicted theoretically. The lack of general theoretical treatment of droplet processes has led to the development of numerous empirical correlations for droplet properties as a function of process parameters and material properties. In this chapter, empirical and analytical correlations for the prediction of droplet properties, such as droplet size distribution and droplet deformation characteristics will be summarized from experimental observations and theoretical analyses in available literature. 

In this chapter, basic theoretical calculations and numerical modeling of droplet generation and deformation processes of both normal liquids and melts will be discussed in detail. The review of modeling efforts will outline the current status and recent developments... 

To detemiine the rate constants of coalescence, a, Danov et examined the effects of droplet interactions and Brownian motion on the coalescence rate in dilnte emnlsions of micrometer- and snbmicrometer-sized droplets. The processes of film formation, thinning, and rupture were included as consecutive stages in the scheme of coalescence. Expressions for the interaction energy due to the various DLVO and non-DLVO surface forces between two deformed droplets were obtained (see also Section 5.4 above). 

Figure 29.6 shows an example of one of the 2D droplet deformation studies carried out specifically for the purpose of modeling the LnCT by Sarchami et al. [9]. The flow conditions for this case are more extreme than can be handled by the theoretical methods for droplet deformation. As the figure shows, not only can these types of results be used to obtain information about jet deformation and trajectory, but they also provide an estimate for the size of the droplets and ligaments that form due to shear breakup at the tips of the elongated cross section. They also show the pattern of the flow field around the droplet. Of particular interest are the double vortices that form behind the droplet and help stretching it out and into a thin shape. The formation of these vortices can play an important role in the secondary atomization processes of the droplets formed in the lee-side of the jet (2D drop). 

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