Nozzle perforated plates

Dispersions may be classified into two types, based upon size range of the droplets formed. Turbulence creators (mixing impellers, mixing valves, eductors, orifice plates) will produce fine emulsions of micron-size droplets. Nozzles, perforated plates, bubble caps, tower packings, etc., can form discrete drops of relatively large size which will quickly settle through the continuous phase. 

For air flow impinging normally to the surface from slots, nozzles, or perforated plates, the heat-transfer coefficient can be obtained from the data of Friedman and Mueller (Proceedings of the General Discussion on Heat Transfer, Institution of Mechanical Engineers, London, and American Society of Mechanical Engineers, New York, 1951, pp. 138-142). These investigators give... 

Bubble Reactors In bubble columns the gas is dispersed by nozzles or spargers without mechanical agitation. In order to improve the operation, redispersion at intei vals may be effected by static mixers, such as perforated plates. The liquid may be clear or be a slurry. 

Compact air jets are formed by cylindrical tubes, nozzles, and square or rectangular openings with a small aspect ratio that are unshaded or shaded by perforated plates, grills, etc. Compact air jets are three-dimensional and axisymmetric at least at some distance from the diffuser opening. The maximum velocity in the cross-section of the compact jet is on the axis. 

Figure 3.29 Gas-phase distributors (a) porous plate, (b) perforated plate, (c) single-orifice nozzle, (d) spider-type sparger, and (e) multiple-orifice nozzle...

Fig. 13. Multistage spout-fluid-bed reactor. 1, spouted bed 2, perforated plate 3, spray nozzle 4, air header 5, fluidized bed.

Kostiuk et al. [40] measured experimentally the flow field of the vertical co-axial turbulent impinging streams with a two-component Laser Doppler velocity meter. The opposing gas streams were ejected from two burner nozzles, which were designed to produce a uniform axial velocity profile at their exits. The turbulence in the flow was generated by a perforated plate located at the end of the contraction section in each nozzle. The air velocity at the exit of the nozzle was varied from 4.1 to 11.4 m s and... 

Arrays with multiple oblique impinging jets are generated via 3-D channel networks which feed fluid from a reservoir via the outlet nozzles of the network into a mixing chamber (see Figures 1.196 and 1.197) [54], Perforated plates contain such arrays. 

Packed-tower efficiency and turndown are strongly dependent on the quality of initial liquid distribution. Uneven distribution may cause local variations in the liquid/gas ratio, localized pinch conditions, and reduced vapor-liquid contact. Figure 14 shows two common liquid distributor types, the ladder type (shown as the top distributor) and the orifice type (shown as the redistributor). The ladder type is a horizontal header of pipes, which are perforated on the underside. The orifice type is a flat perforated plate equipped with round or rectangular risers for gas passage. Other common types of distributors are a header equipped with spray nozzles (spray distributor) and a header of horizontal channels, with V notches cut in the vertical walls of the channels (notched-trough distributor). 

The various components of a typical fluid bed spray granulation unit are depicted in Fig. 7.8. Fluidizing gas (usually air) at 2 or 3 psig (14 to 21 kPa) is heated externally to the fluid bed and passes to the base of the unit. Here a suitable distributor such as a perforated plate or tubes with nozzles passes the gas to the particle bed uniformly over its cross-section. Jets formed at... 

Fig. 7.9. Batch fluid bed spray granulator used to produce tablet granulations in the pharmaceutical industry. Air-flow necessary for fluidization is generated by a suction-fan (2) mounted in the top portion of the unit, directly driven by an electric motor. The air being used is heated to the desired temperature by an air heater (5). Prefilters remove all impurities at the air inlet (6). The material to be processed has been loaded into the material container (1). The container bottom consists of a perforated plate above which a fine mesh stainless steel retaining screen is fitted. Exhaust filters (7) mounted above the product container retain fines and dust. The granulating liquid (3) is sprayed as a fine mist through a mechanical or pneumatically actuated nozzle (4) onto the finely dispersed, fluidized material to form the desired agglomerates. (Courtesy Aeromatic AG.)...

Figure 4. Industrial gas distributors (A) perforated plate (B) nozzle plate (C) bubble-cap plate.

In eq 10, ho is the height above the grid where the bubbles form (for a porous plate, ho = 0 for a perforated plate, ho = L for a nozzle plate, ho is the height of the outlet opening above the plate and for a bubble-cap plate, ho is the height of the lower edge of the cap above the plate). 

FIGURE 9.2 Nozzles for sprays and units for aeration or stripping (a-d) nozzle types (e) inclined apron that may be studded with riffle plates (f) perforated plates (g) spray tower and (h) cascade. 

The lateral distributions of bubble holdup in fluid beds are very similar to those of bubble columns for gas-liquid systems. Experimental results by Akehata et al. (A2), Pozin et al. (P6), Ivanov and Bykov (112), Yamagoshi (Y2), Miyauchi and Shyu (M31), Hills (H9), Kato et al. (K7) and Ueyama and Miyauchi (U3) are reasonably well expressed by Eq. (2-13). When a gas phase is distributed with a perforated plate or a nozzle sparger, the parameters in Eq. (2-13) for the bubble columns are in the range of n = 1.7-2.5. 

Fig. 39. Longitudinal dispersion coefficients of liquid in bubble columns (SN = single nozzle PP = perforated plate). The full circles are calculated with the use of Eq. (4-12).

Axial distribution of kobOb has been shown to have only a minor effect on the performance of fluid catalyst reactors (K14, M28). It has been shown in Section II that (a) bubbles from a single nozzle break up in rising a certain distance to attain a final size (b) bubbles from a perforated plate associate together when rising and (c) stays fairly constant axially thereafter. 

The target quantity of the gassing process is the absorption rate in the gas/liquid (G/L) system. It is directly proportional to the interfacial area between the gas phase and the liquid phase. The limiting factor is the diffusion of the dissolved gas through the liquid-side of the boundary layer, which can only be affected by its thickness to a limited extent. A substantial intensification of mass transfer is only possible by increasing the G/L interfacial area gas sparging by means of stirrers, nozzles, sintered or perforated plates etc. should therefore effect a dispersion of the gas into fine bubbles. 

The two identical nozzles and their dimensions described previously [2] had contractions of area ratio 9.0 and followed a fifth-order polynomial [3] to a diameter of 25 mm. Fig. 6.1. The nozzle separation was varied between 0.2 and 2.0 exit diameters with bulk velocities from 1.49 to 7.00 m/s, and, since these velocities corresponded to Reynolds numbers of 2,000 and 10,000, a perforated plate was located at the end of the contraction with 4-millimeter diameter holes and 50% solidity. A subsequent straight pipe, two exit diameters in length, allowed the wakes to diminish and the small-scale turbulence to develop [4]. The two jets were mounted on a frame that allowed the separation to be varied while maintaining the same geometric axis. The compressed air and gas supply of natural methane was filtered, and the flow was measured with calibrated rotameters to accuracy better than 3%, while the centerline velocities were matched within 0.1 m/s. 

The fuel and air mixture leaves the vaporizer and is fed to the combustor assembly, which consists of a diffuser, plenum with flow conditioning, nozzle, and combustor test section. The diffuser transits the flow from a 50.8-millimeter circular duct to a 160 X 120 mm rectangular-shaped plenum. The flow conditioning consists of two perforated plates, which enhance the flow uniformity and serve as effective flame arresters. The two-dimensional nozzle is constructed from sectors of a large-radius pipe and has an area ratio of 6 1. Pitot probe surveys showed that this setup produced a uniform top-hat velocity distribution across the area of the nozzle exit [2],... 

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