External-mixing

Atomizers for large boiler burners are usually of the swid pressure jet or internally mixed twin-fluid types, producing hoUow conical sprays. Less common are the externally mixed twin-fluid types (89,90). 

Figure 5 Schematic diagrams of reactors used in FIA in order of increasing dispersion (a) single bed string reactor, (b) knitted tube, (c) coiled tube, (d) straight tube, and (e) external mixing chamber with stirring.

Figure 2.7. Schematic of external-mixing two-fluid atomizers.

A variety of atomizer designs have been developed in an effort to control the droplet size distribution and to increase the yield of fine powders. Gas atomizers used for the atomization of melts may be loosely classified into two primary categories in terms of the interaction mode between a liquid metal and an atomization gas during atomization, i.e., (1) internal mixing and (2) external mixing. 

Configuration External Mixing Free-Fall Annular Cone Jet Symmetric Discrete Fan-Spray Jets (V Jets) Asymmetric Cross Jets (Horizontal)... 

External-mixing air-assist atomizers. Derived from ethanol (glycerin)-air spray data with initial thickness of flat circular sheet up to 0.7 mm and varied air impingement angles Sampled with oil-coated slides... 

For high-frequency measurements, normal photomultipliers are too slow, and microchannel plate photomultipliers are required. However, internal crosscorrelation is not possible with the latter and an external mixing circuit must be used. 

Fan-spray nozzles Spinning cups External mixing... 

Two peaks in the accumulation mode may also result if the particles are externally mixed rather than internally mixed (the latter meaning that all particles have the same composition corresponding to a mixture of the various components). That is, the composition of individual particles may not be the same as the overall bulk particle composition, with some having more hygroscopic components than others. These are referred to as externally mixed particles indeed single-particle analyses suggest that externally mixed particles are common (see Chapter 11.B.4). In this case, a... 

The negative exponent on the Reynolds number of -0.32 indicates that Re has a medium effect on the mean diameter. This result is about in accordance with those obtained by Gretzinger and Marshall [801 in their investigation on the external mixing pneumatic spray nozzles. 

According to its working principles, the nozzle shown in Fig. 7.5 should be classified as a three-flow internal-external mixing nozzle Berman and co-workers called it a complete external mixing type . 

As with external mixed convection, the influence of buoyancy forces on the flow depends on the angle that the buoyancy forces makes to the direction of the forced flow. The heat transfer rate also, of course, depends on the duct cross-sectional shape as well as on whether the flow is laminar or turbulent. 

FIGURE 3 Atomization nozzle designs for internal mixing and external mixing... 

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