Hydraulic Pressure Nozzles

Hydraulic (Pressure) Nozzles Manufacturers data such as shown by Fig. 14-88 are available for most nozzles for the air-water system. In Fig. 14-88, note the much coarser solid-cone spray. The coarseness results from the less uniform discharge. 

Hydraulic pressure nozzles cannot combine the capability for fine atomization with high feed capacity in one single unit. Many spray dryer applications, where pressure nozzles are applied, therefore require multinozzle systems with the consequence that start-up, operational control, and shutdown procedures become more complicated. 

For hydraulic pressure nozzles the following formula proposed by Lefebvre may be used ... 

For a fixed-orifice conventional hydraulic pressure nozzle operating with a given spray liquid, the only way in which flow rate through the nozzle can be changed is by varying the pressure at the nozzle. However, variations in operating pressure result in changes to both the spray volume distribution pattern (pattemation), the droplet size (spray quality) and velocity distributions (see Table 4.2). 

Spray dryers with nozzle atomizers use two different types of dispersers singlephase, hydraulic pressure nozzles and two-phase, pressurized gas assisted nozzles (see also Section 7.4.2). The latter has a relatively limited application in spray drying because of the relatively large flow of atomizing gas, which influences the flow pattern of the drying gas in the tower, and the broader particle size distribution that is produced by this type of nozzle. 

Fig. 7.57 Photograph of a single phase, hydraulic pressure nozzle in operation (courtesy CEA/NIRO, Soeborg, Denmark).

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