Ligament formation

In rotary or centrifugal atomization, droplet formation may follow several distinct mechanisms, as proposed by many research-ers 94 l09l"l, 2I on the basis of experimental observations of rotating flat disk process (Fig. 3.9) (a) Direct Droplet Formation, (b) Direct Droplet and Ligament Formation, (c) Ligament Formation, and... 

Table 4.11b. Correlations for Mean and Maximum Droplet Sizes Generated by Smooth Flat Vaneless Disks in Ligament Formation Regime...

Accordingly, for the transition from Direct Droplet to Ligament Formation regime and the reverse transition, the dimensionless transition flow rates are Q = 0.096 Re0,95/We115 and Q = 0.073 Re°-95/We115, respectively.[470]... 

FIGURE 6.3 Mechanisms of drop formation by spinning disk atomization, (a) Direct formation, (b) ligament formation, and (c) sheet formation. (Reproduced from Teunou, E. and Poncelet, D., J. Food Eng, 71(4), 345, 2005. With permission.)... 

Senuma also reported that in the ligament formation regime, drop size resulting from the breakup of the ligaments in disk atomization is, according to Weber s theory, given by Equation 6.19... 

A. Frost. Rotary atomization in the ligament formation mode. Journal of Agricultural Engineering Research, 26(l) 63-78, January 1981. 

It is observed that the breakup time is reduced as the Weber number is increased, which is expected. It is now evident that the liquid sheet breakup occurs at halfwavelength intervals, as observed earlier, and this parcel of liquid is expected to contract into a ligament under the force of surface tension. There does not exist any indication of satellite ligament formation from the liquid sheet breakup. 

Fig. 24.50 Plot of 24.8.V for ligament formation atomization, plotted at different values of disk diameter against (a) rotational speed, (b) volumetric flow rate. Properties N = 15,000 rpm, Q = 0.05 m /s...

Matsumoto and Takashima [83] proposed an equation for ligament formation, in which the diameter of the ligament is also considered. Equation 24.4.i for effervescent and swirl nozzles greatly resembles this correlation. 

For the rotating cage type of nozzle, Hewitt found two correlatiOTis for the VMD one for when atomization was achieved by drop formation 24.ll.iii, and one for ligament formation 24.1 l.iv. The formula for droplet formation is the only one of the formulas derived by Hewitt that considers the liquid properties. It considers the effect of surface tension and liquid viscosity. According to Hewitt, liquid properties become insignificant at higher modes of atomization. It is interesting to note that tmder droplet formation, Hewitt states that the volumetric flow rate has very little... 

Disk must be flat and vaneless Neglects effect of liquid viscosity Atomization must occur by droplet formation Disk must be flat and vaneless atomization must occur by ligament formation... 

Disk must be vaneless but not necessarily smooth or flat Atomization must be achieved by ligament formation... 

A review of the past literature on the available correlations on the mean droplet size produced by splash plate nozzles shows that there are large discrepancies between the results. The prediction of the droplet sizes generated by splash plate nozzles is based on the Kelvin-Helmholtz (K-H) instability theory for a liquid sheet. Dombrowski and Johns [14], Dombrowski and Hooper [18] and Fraser et al. [13] developed such a theoretical model to predict droplet sizes from the breakup of a liquid sheet. They considered effects of liquid inertia, shear viscosity, surface tension and aerodynamic forces on the sheet breakup and ligament formation. Dombrowski and Johns [14] obtained the following equation for droplets produced by a viscous liquid sheet ... 

Figure 9 Smooth disk atomizer droplet formation mechanisms (A) direct droplet formation, (B) ligament formation, and (C) sheet formation. (From Ref. 12.)...

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