Liquid sheet

Unmodified Modified Sheet Standard cushioning Carpet underlay High resilience type PVC b Liquid Sheet ... 

Liquid-Sheet Breakup The basic principle of most hydraulic atomizers is to form a thin sheet that breaks via a variety of mechanisms to form ligaments of liquid which in turn yield chains of droplets. See Fig. 14-86. 

FIG. 27-24 Idealized process of drop formation by breakup of a liquid sheet. After Domhrowski and Johns, Chem. Eng. Sci. 18 203, 1963. )... 

A limited number of polyanion-polycation systems were tested using a droplet/falling annulus method (Fig. 4). This technique, which has been described elsewhere [64] reduces the net impact velocity between the droplet with the oppositely charged counterion fluid. A stream of droplets was directed into a collapsing annular liquid sheet. By matching the velocities of the droplet and sheets, the impact conditions can be moderated. It has been shown to produce monodisperse spherical capsules, though it requires several days of calibration for each new system and is obviously not practical for a massive screening such as was carried out herein. 

Roller atomization is a mechanical atomization process. It was invented in the mid 1970 sJ188] In this process, as schematically depicted in Fig. 2.22, a stream of molten metal is fed into the gap between two counter-rotating rolls and forms a thin liquid sheet that subsequently disintegrates into droplets by the mechanical forces. In the original design, a pair of rollers of 100 mm in diameter are mounted in the same horizontal plane and rotate at speeds up to 1250 radians/s. The roll gap is about 50-100 pm, and the metal flow rate is up to 6 kg/min. 

Table 3.2. Classification and Criteria of Breakup Regimes of Round Liquid Jets in Co-flowing Air as Compared to Those of Thin Liquid Sheets and Spherical Droplets in Air Stream 210 ...

Figure 3.8. Liquid sheet/film breakup modes Successive stages in the idealized breakup of (a) a sheet with a thick rim, (b) a wavy sheet, and (c) a perforated sheet.

Taylor and Michael1254 analyzed the perforation process based on a balance of forces acting on a hole in a liquid sheet. The analysis showed that any hole with a radius greater than the thickness of the liquid sheet would grow, whereas smaller holes would close. Experiments also demonstrated the existence of a minimum initial hole size for growth to occur. 

Taylod205 also conducted mathematical analysis of the generation of ripples by wind blowing over a viscous fluid. Using a relationship between the growth of the amplitude of disturbance waves and the surface stress, Taylor derived a criterion for the instability of waves. In Taylor s instability theory, the disintegration of a liquid sheet/film is visualized as a process in which droplets are detached from the liquid surface with a wave of optimum amplitude. The diameter of the most frequent droplets is then formulated as a function of air velocity over the liquid surface, liquid density, surface tension and viscosity, as well as air density. 

As indicated by Mansour and Chigier,12091 all previous experimental studies focused onflat liquid sheets into quiescent air. In many industrial applications, liquid sheets are injected into air streams... 

A) Flat Liquid Sheets into Quiescent Air Rim-Jet Disintegration. In quiescent air (without an air flow), a liquid sheet issuing from the 2-D nozzle will converge toward the axis of the sheet to form a round j et under the action of surface tension forces. The liquid jet subsequently breaks up into droplets. 

The aerodynamic breakup mode occurs in the liquid sheet between the rims. In aerodynamic breakup, the perforation and wave... 

Although a liquid sheet may leave the nozzle with some perturbations, the principal cause of the instabilities is the interaction of the sheet with the high-velocity air streams whereby rapidly growing waves are imposed on the sheet. Disintegration may occur when the amplitude of these waves reaches a critical value. Each full sinusoidal wave is initially distorted to yield two half-waves of very similar forms. The constant stretching of the half-waves increases... 

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. 

Flat Sheets. Generally, the interface between a liquid sheet and air can be perturbed by aerodynamic, turbulent, inertial, surface tension, viscous, acoustic, or electrical forces. The stability of the sheet and the growth rate of unstable disturbances are determined by the relative magnitude of these forces. Theoretical and experimental studies 255112561 on disintegration mechanisms of flat sheets showed that the instability and wave formation at the interface between the continuous and discontinuous phases are the maj or factors leading to... 

Weiss and Worsham 259 indicated that the most important factor governing mean droplet size in a spray is the relative velocity between air and liquid, and droplet size distribution depends on the range of excitable wavelengths on the surface of a liquid sheet. The shorter wavelength limit is due to viscous damping, whereas the longer wavelengths are limited by inertia effects. 

Arai and Hashimoto[2611 studied disintegration of a thin liquid sheet in a co-flowing air stream. For a constant sheet thickness, an empirical correlation was derived for the sheet breakup length as ... 

---