Droplets satellite

Consider drops of different sizes in a mixture exposed to a 2D extensional flow. The mode of breakup depends on the drop sizes. Large drops (R > Caa,tal/xcy) are stretched into long threads by the flow and undergo capillary breakup, while smaller drops (R Cacri,oV/vy) experience breakup by necking. As a limit case, we consider necking to result in binary breakup, i.e., two daughter droplets and no satellite droplets are produced on breakup. The drop size of the daughter droplets is then... 

Fig. 23. (a) Distribution of drop sizes for mother droplets and satellite droplets (solid lines) produced during the breakup of a filament (average size = 2 x 10 5 m) in a chaotic flow. The total distribution is also shown (dashed line). A log-normal distribution of stretching with a mean stretch of 10 4 was used, (b) The cumulative distribution of mother droplets and satellite droplets (solid line) approaches a log-normal distribution (dashed line). 

Rotary Atomization Spinning Disk 10-200 Spray drying. Aerial distribution of pesticides. Chemical processing Good mono-dispersity of droplets. Independent control of atomization quality and liquid flow rate Satellite droplets, 360° spray pattern... 

Recently, Razumovskid441 studied the shape of drops, and satellite droplets formed by forced capillary breakup of a liquid jet. On the basis of an instability analysis, Teng et al.[442] derived a simple equation for the prediction of droplet size from the breakup of cylindrical liquid jets at low-velocities. The equation correlates droplet size to a modified Ohnesorge number, and is applicable to both liquid-in-liquid, and liquid-in-gas jets of Newtonian or non-Newtonian fluids. Yamane et al.[439] measured Sauter mean diameter, and air-entrainment characteristics of non-evaporating unsteady dense sprays by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on the Sauter mean diameter and air entrainment were investigated parametrically. An empirical equation for the Sauter mean diameter was proposed based on a dimensionless analysis of the experimental results. It was indicated that the Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It was also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory. 

Small satellite droplets, which are produced along with the uniform size larger droplets when ligaments break, can easily be removed. Droplet sizes from 15 microns to 3 mm. have been produced. The proportion and size of satellite droplets increase with increased liquid flow rates until a flow is reached where separation is no longer possible. Liquid viscosity plays a negligible role. 

The breakup or bursting of liquid droplets suspended in liquids undergoing shear flow has been studied and observed by many researchers beginning with the classic work of G. I. Taylor in the 1930s. For low viscosity drops, two mechanisms of breakup were identified at critical capillary number values. In the first one, the pointed droplet ends release a stream of smaller droplets termed tip streaming whereas, in the second mechanism the drop breaks into two main fragments and one or more satellite droplets. Strictly inviscid droplets such as gas bubbles were found to be stable at all conditions. It must be recalled, however, that gas bubbles are compressible and soluble, and this may play a role in the relief of hydrodynamic instabilities. The relative stability of gas bubbles in shear flow was confirmed experimentally by Canedo et al. (36). They could stretch a bubble all around the cylinder in a Couette flow apparatus without any signs of breakup. Of course, in a real devolatilizer, the flow is not a steady simple shear flow and bubble breakup is more likely to take place. 

Both the initial droplet formation and the thread break-up and formation of satellite droplets occurred much quicker than observed for the horizontal tube case. In the case of horizontal tubes, surface tension in the... 

The spinning-disk method of droplet generation is based on the breakup of ligaments of liquid created at the periphery of a rapidly rotating disk when liquid is fed slowly to the center and top of the disk. Under appropriate conditions of stable liquid feed and rotation, the ligament thrown out by the rotating disk breaks up into a primary (large) and a satellite (small) droplet. This is illustrated in Fig. 7. The satellite droplet is deflected away by an airflow and is usually rejected. 

The primary stream of droplets is monodisperse. Walton and Prewett [49] demonstrated this principle of uniform droplet generation. An improved version with a spinning top was developed by May [50,51]. Further improved versions have been developed since then, and droplet sizes that are produced range from 15 to 150 pm (e.g., see Ref. [52]). A recent version produced monodisperse droplets between 10 and 60 pm in diameter [53]. Similar particles can be obtained using solutions. Toivonen and Bailey produced solid particles up to 40 pm in diameter [54]. Rotation speeds used are up to 70,000 rpm. Improvements in particle concentrations have been obtained by Cheah and Davies [55] but are still nominally less than 100 cm-3. A detailed study of the mechanism of droplet formation was provided recently by Davies and Cheah [56]. Eisner and Martonen [57] demonstrated that if the primary and satellite droplets can be effectively separated, then two monodisperse aerosol streams can be generated simultaneously. 

Separate large- and small-drop aerosols can be produced by taking advantage of the different stop distances of the primary and satellite droplets. Aerosols of the original pure liquids can be produced in this way with primary droplet diameters ranging from 6 to 3000 / im and liquid flow rates up to 168 cmVmin. When solutions with volatile solvents are used, the solvents can be evaporated, leaving behind particles whose size depends on the... 

Even if the jet velocity is low enough that just capillary forces need be accounted for, the hydrodynamic stability problem is relatively simple when only the jet stability to small disturbances is considered, that is, disturbances whose amplitudes are small compared with the jet radius. When this is not the case, nonlinear mechanisms enter, which are manifest in various phenomena, including the formation of satellite droplets, which are small spherules that form between the drops (Fig. 10.4.2B). For literature on these and other nonlinear effects of jet instability, see Bogy (1979). 

Figure 10.4.2 Photographs of liquid jet breakup in air (A) into spherical drops. [Courtesy of Prof. Richard K. Chang. From Qian, S-X. et al. 1986. Lasing droplets Highlighting the liquid-air interface by laser emission. Science 231, 486-488. Copyright 1986 by the AAAS. With permission.] (B) into spherical drops with satellite droplets. [Courtesy of Prof. M.C. Yuen. From Goedde, E.F. Yuen, M.C. 1970. Experiments on liquid jet instability. /. Fluid Mech. 40, 495-511. Cambridge University Press. With permission.]...

---