Sheet disintegration

Fraser et aU116 207 defined three modes of sheet disintegration, as schematically depicted in Fig. 3.8. 

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... 

Short wavelengths of disturbance on thick sheets are stable unless wind velocities or Weber numbers are very high. The optimum wavelength for sheet disintegration corresponds to the maximum growth rate /3max. For We 1, these are formulated as 258 ... 

In both atomization modes, as thin unstable ligaments, and/ or sheets disintegrate into round droplets, atomization gas may plausibly be trapped into the droplets under certain conditions. For alloys with alloying elements which readily react with atomization gas, for example, oxidize to form refractory oxides, solidification may be delayed and spheroidization is prevented so that rough flakes may form. For such alloys, the atmosphere in the spray chamber must be inert and protective to avoid the formation of any refractory and to foster spheroidal shape of droplets. 

Droplet Formation in Centrifugal Atomization. The mechanisms of centrifugal atomization of liquid metals are quite similar to those for normal liquids. Three atomization modes have been identified in rotating electrode atomization process, i.e., (I) Direct Droplet Formation, (2) Ligament Disintegration, and (3) Film/Sheet Disintegration.1[189][32°] are aiso applicable to the centrifugal atomiza-... 

Figure 4.3. Regimes in centrifugal atomization of melts Direct Droplet Formation, Ligament Disintegration, and Film/Sheet Disintegration.

In perforated-sheet disintegration shown in Figure 16.19b, small holes suddenly appear in the sheet as it advances into the atmosphere. They rapidly grow in size(36) until the thickening rims of adjacent holes coalesce to form threads of varying diameter. The threads finally break down into drops. 

The influence of conditions on the droplet size where the spray sheet disintegrates through aerodynamic wave motion may be represented by the following expression proposed by Dombrowski and Monday134 for ambient densities around normal atmospheric conditions ... 

At low-discharge velocities and low film thicknesses, the sheet disintegration is due to the oscillations caused by air motion. In this case, the film thickness has a large impact on the droplet size. In contrast, it is insignificant whether a pure liquid or a lime-water suspension (mass portion cj) = 16-64%) is treated (21). 

I an Sprays, It was demonstrated around the 1950s that instabiHty theory can be used to analyze the wave growth on a thin Hquid sheet (18). This analysis predicted the existence of an optimum wavelength at which a wave would grow rapidly. This optimum wavelength, X corresponds to a condition that leads to Hquid sheet disintegration. It can be expressed as in equation 2 ... 

Drops in a typical hydraulic nozzle are formed in a liquid sheet that travels at 15-25 m/s. Following sheet disintegration, drops move in an air-jet caused by the interaction of the spray plume and the surrounding air. Close to the nozzle,... 

Hege [82] derived 24.8.v for the MMD of a spray. His formula applied for sheet disintegration only, and is a function of angular velocity, surface tension, liquid density and disk diameter. 

The only available formula for the SMD of a rotary nozzle undergoing sheet disintegration is by Tanasawa et al. [78] 24.8.vi, which is plotted in Fig. 24.52. The equation is not too dissimilar to the equation derived by the same author for droplet formation. The a/ipid) ratio exists in both however in droplet formation, it is raised to 0.5, while in sheet formation, it is raised to 0.4. The major difference between the... 

Fig. 24.52 A plot of 24.8.ii for sheet disintegration at various values of disk diameter, plotted against (a) rotational speed and (b) volumetric flow rate...

I-P. Chung, C. Presser, Fluid property effects on sheet disintegration of a simplex pressure-swirl atomizer, J. Propuls. Power 17(1), 212-216 (2001). 

Huang TC, Watkins ND, Shaw DM (1975) Atmospherically transported volcanic glass in deep-sea sediments Volcanism in subantarctic latitudes of the Pacific during late Pliocene and Pleistocene time. Geol Soc Amer BuU 86 1305-1315 Hughes T (1973) Is the West Antarctic ice sheet disintegrating J Geophys Res 78 7884-7910... 

To investigate the influence of a dispersed water phase on the sheet disintegration, experiments have also been carried out with concentrated water in oil emulsions. The concentration of the dispersed phase was varied between 0 and 50 wt% as was the saturation pressure. Rapeseed oil was used as a continuous oil phase, and water as a dispersed one. Figure 15.42 shows the disintegration of the emulsimi at a saturation pressure of 5 MPa and 333 K. For better representations, the images have been cropped and only show an area after the nozzle of 12 mm x 32 mm. 

At elevated temperatuies, high-puiity water can have an adverse effect on many aluminum alloys. At 200 °C (390 °F), high fuiity aluminum sheet disintegrates within a few days with the formation of alumi-... 

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