Droplet size uniform distribution

The spray nozzle (or nozzles) in the production machine would need to be of a size such that this increased spray rate is within its performance envelope (similar droplet size, uniform in distribution), or equivalence in granule size would be impossible. Figure 17 illustrates the concept that atomizing air pressure must be adjusted to attain similar average droplet sizes in all three scales of process equipment at the desired spray rate (data from... 

Experimental methods presented in the literature may prove of value in combustion studies of both solid and liquid suspensions. Such suspensions include the common liquid spray. Uniform droplets can be produced by aerosol generators, spinning disks, vibrating capillary tubes, and other techniques. Mechanical, physicochemical, optical, and electrical means are available for determination of droplet size and distribution. The size distribution, aggregation, and electrical properties of suspended particles are discussed as well as their flow and metering characteristics. The study of continuous fuel sprays includes both analytical and experimental procedures. Rayleigh s work on liquid jet breakup is reviewed and its subsequent verification and limitations are shown. 

An emulsion is a dispersed system where one liquid phase is finely subdivided as globules or droplets and uniformly distributed in the other liquid phase. The practical application of emulsions and their technology applies to pharmaceutical and cosmetic formulations. The usual globular or droplet sizes range from 0.1 to 10 pm. 

Dropsize Distribution Monodisperse (nearly uniform droplet size) fogs can be grown by providing a long retention time for growth. However, industrial fogs usually show a broad distribution, as in Fig. 14-91. Note also that for this set of data, the sizes are several orders of magnitude smaller than those shown earlier for entrainment and atomizers. 

In terms of measuring emulsion microstructure, ultrasonics is complementary to NMRI in that it is sensitive to droplet flocculation [54], which is the aggregation of droplets into clusters, or floes, without the occurrence of droplet fusion, or coalescence, as described earlier. Flocculation is an emulsion destabilization mechanism because it disrupts the uniform dispersion of discrete droplets. Furthermore, flocculation promotes creaming in the emulsion, as large clusters of droplets separate rapidly from the continuous phase, and also promotes coalescence, because droplets inside the clusters are in close contact for long periods of time. Ideally, a full characterization of an emulsion would include NMRI measurements of droplet size distributions, which only depend on the interior dimensions of the droplets and therefore are independent of flocculation, and also ultrasonic spectroscopy, which can characterize flocculation properties. 

Eadie, in Ref 69, reports on a considerable amount of work done on the ability of beeswax and paraffin wax to remain coated on HMX surfaces when immersed in liq TNT. Thru measurements of contact angles, a technique used earlier on RDX/wax systems reported on by Rubin in Ref 23, it was determined that the TNT preferentially wets the HMX and the wax is stripped away. He concludes that the most important property of a desensitizing wax is that it should be readily dispersed uniformly thruout the TNT phase. He also suggests that a better desensitizer for investigation for use would be a wax or substituted hydrocarbon having a low interfacial tension with TNT. The smaller the wax droplet size the more efficiently it will be distributed and the more effectively it should desensitize. Williamson (Ref 64) in his examination of the microstructures of PETN/TNT/wax fusion-casts detected that wax is dispersed thru the cast as isolated descrete globules which he refers to as blebs or irregular or streak-like areas, surrounded by TNT (see also Ref 54)... 

Distribution of Sizes. Although special techniques can in some cases produce nearly uniform suspensions, most spray combustion research must be conducted on systems composed of a wide range of droplet sizes. A knowledge of the distribution of particle size is of great importance. 

It can be seen from the figures that the size distributions of spray droplets become narrower after impingement, or, in other words, the droplet sizes become more uniform than before. Such a variation is observed in most of the runs, although some exceptions also appeared (about 10% in all the runs). As is well known, the uniformity of droplet sizes, or inversely, the scattering of the size distribution can be expressed with the parameter Standard Deviation , a, which is the defined as... 

The larger the value for cr, the greater the scattering of the size distribution, and, correspondingly, the poorer the uniformity of the droplet sizes. Part of the data measured at various air-to-liquid mass flow ratio, m.JmL, are shown in Table 5.1. It can be seen that, normally, the impingement between opposing droplets-in-gas suspension streams makes cr smaller. Only those obtained at in the third column of the... 

Another interesting result observed is that in the case without impingement, i.e., only primary atomization occurred, the scattering of the droplet size distribution, a, decreases, and, consequentially, the droplet sizes become more uniform, as the gas to liquid mass flow rate ratio, increases, as can be seen in the third row of Table... 

The impingement between the two opposing suspension streams makes the sizes of the spray droplets uniform to an extent, yielding narrower size distribution. More intensive impingement favors the uniformization of droplet sizes more effectively. 

A model for wet scrubbing in a cross-flow is illustrated in Fig. 7.21. Consider a rectangular scrubbing domain of length L, height H, and width of unity in Cartesian coordinates. Assume that the gas-solid suspension flow is moving horizontally, and that the solid particles are spherical and of uniform size. The particle concentration across any plane perpendicular to the flow is assumed to be uniform. The water droplets fall vertically and are uniformly distributed in the flow system. 

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