Spray periphery

A comparison has been made of detailed CFD predictions, which have included all the aerodynamic processes involved in falling sprays, and a simple momentum conservation model which ignores the induced shear flow on the spray periphery. This has shown that for the scenarios considered here it is adequate to use the latter, simpler treatment, which is described in Annex 1. Typical results obtained using the simple momentum conservation model are shown in Figure 16. In overfilling incidents the mass flux density is likely to be in the range 1 to 10 kg/mVs. This corresponds to maximum droplet velocities of 10-13 m/s and vapour velocities of 4-6 m/s. 

In order to provide further evidence on the results discussed above, the gas flow now is fully coupled to the spray equations. Figure 9.14 shows a comparison of the experimental and numerical profiles of the axial droplet velocity for the PVP-water spray with 10 % PVP mass fraction and an injection pressure of 25 bar at the cross-section of 120 mm after the nozzle exit. The figure shows both the numerical simulations without and with coupling of the DQMOM to the gas phase Eqs. (9.27)-(9.30). It can be observed that the results are greatly improved by resolving the gas phase. However, at the periphery of the spray the computed axial droplet velocity differs stiU about 3 m/s from the experimental results. This is explained by inconsistent boundary conditions the simulations correspond to a confined jet while the experiments represent a free jet. Moreover, at the spray periphery, the experimental error is larger than in the spray center. 

D, 5 = average drop diameter, ft / = disk radius, ft F = spray mass velocity, lb/(min ft of wetted disk periphery) P/ = hquid density, Ib/fo N = disk speed, r/min p = hquia viscosity, lb/(ft min) a = surface tension, Ib/min"... 

In all metal spraying processes the particles emerge from the nozzle in a conical stream, and although the particles near the centre are molten, those at the periphery have solidified. In the powder process there are in addition solid particles which have not melted. The solid particles tend to become entrapped in the coating, making it porous. The effect is more pronounced in the powder process owing to the larger number of solid particles present. 

Rotary Cup 10-320 [73] [74] Spray drying. Spray cooling Capable of handling slurries Possible requirement for air blast around periphery... 

Solid-cone spray atomizers usually generate relatively coarse droplets. In addition, the droplets in the center of the spray cone are larger than those in the periphery. In contrast, hollow-cone spray atomizers produce finer droplets, and the radial liquid distribution is also preferred for many industrial applications, particularly for combustion applications. However, in a simplex atomizer, the liquid flow rate varies as the square root of the injection pressure. To double the flow rate, a fourfold increase in the injection pressure is... 

Spinning Disk Atomization. The spinning disk produces a continuous spray which spreads radially outwards from the periphery of the disk. A major difference of this technique in comparison with pressure atomization of liquids is mentioned by Marshall and Seltzer (5F), who give a detailed theory of atomization for both smooth and vaned disks. High velocities are achieved without a pressure increase. 

Micrographs obtained by EPMA are shown in Figure 4. The sample in this case was VPO with 10% amorphous silica as the hard phase. This composition was prepared by spray drying an aqueous slurry with about 40% solids made of l-2 im particles of the VPO catalyst precursor and polysilicic acid. The back-scattered image shows all elements present in the porous microsphere. The X-ray image of silicon clearly shows this element concentrated exclusively on the periphery of the microsphere. Independent X-ray diffraction and electron diffraction analysis of the peripheral layer of the microspheres showed that the silicon is present as amorphous silica. 

The symmetric local mechanical disturbances (tensions) can be normal and tangential. The source of such disturbances in foam films could be an air stream directed normally to the film surface. Then, a local increase in pressure (the normal component of the disturbance) is observed as well as a tangential force that sprays the stream at the film surface (tangential component). As a result of the former the liquid in the film moves from the disturbance zone to its periphery. The process of liquid outflow from the film involves two stages uniform deformation of the disturbed part (i.e. film extension) and liquid outflow by the usual mechanism. The analysis of Krotov [28] indicates that, if the condition h/rd 1 (rb is the radius of the zone of disturbance) is fulfilled, the rate of film thinning as a result of liquid outflow is negligible compared to the rate of film extension. 

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