Hydraulic nozzles

Further differences from hydraulic nozzles (controlled by sheet and ligament breakup) are the stronger increase in drop size with increasing surface tension and decreasing gas density. 

Hi) Hydraulic nozzles tend to atomize effectively at liquid flow rates greater than 250 ml/min, Olsen (1989a,b). 

Vehicle-mounted (with cab) and hydraulic nozzles volume of surface contamination, 10 mL/h inhalation exposure, 0.01 mL/h ... 

Another freezing technique involves spraying the solution directly into liquid The lower temperature could promote more rapid freezing, but this potential advantage is offset by poor thermal contact of the solution with the liquid N2, due to an insulting layer of gas around the solution droplets. A pneumatic rather than hydraulic nozzle can also be used to disperse the solution into a fine aerosol whose droplets can be frozen quickly because of their small size. This technique is less manageable because it is difficult to separate the fine aerosol droplets from the gas before freezing. 

Although wide drop-size distributions can sometimes be an advantage (Hislop, 1983) the large numbers of small drops produced in hydraulic nozzle sprays can result in spray drift and inadequate targeting (Miller, 1993). Rotary atomisers (Bals, 1975) can reduce the breadth of drop-size distributions and provide a more targeted size distribution. They have not been widely adopted in broad-acre ground crops, because their spray volumes and drop trajectories often cause control difficulties, but they have found some acceptance in orchard sprayers. 

Drops in a typical hydraulic nozzle are formed in a liquid sheet that travels at 15-25 m/s. Following sheet disintegration, drops move in an air-jet caused by the interaction of the spray plume and the surrounding air. Close to the nozzle,... 

The most commonly used application systems in arable crops are boom sprayers equipped with equally spaced hydraulic nozzles (Robinson, 1993). The quality of the spray influences the quantity deposited on the crop and spray-drift. The combination of forward speed, nozzle type and pressure defines the sprayed volume. Volume rates have been reducing for several decades. While in the 1950s it was common to spray 10001/ha, nowadays 100-3001/ha is more common. 

Taylor WA and PG Andersen, 1991. Enhancing conventional hydraulic nozzle use with the Twin spray system. In Air-Assisted Spraying in Crop Protection. BCPC Monograph, No. 46, pp. 125-136. 

Where large droplets have to be applied from hydraulic nozzle, lower flight speeds may reduce droplet shatter... 

Laser technology has enabled the rapid assessment of nozzle performance to be undertaken during the last 15 years. By simulating the airflow profile around both centrifugal and hydraulic nozzles in a wind tunnel, the influence of airspeed, formulation and nozzle design has been extensively studied. 

Table 6.5 Droplet spectra generated by hydraulic nozzles in a wind tunnel. Measuring device Malvern 2600 laser diffraction analyser...

Chappie AC, Downer RA and Hall FR Effects of spray adjuvants on swath patterns and droplet spectra for a flat-fan hydraulic nozzle, Crop Protection, 12 579-590 (1993). 

Figure 8.7 Droplet size spectra water +0.1% Agral, atomised by the Herbi rotary atomiser, compared with three hydraulic nozzles. The hydraulic nozzles were scanned diagonally through the centres of the spray fan (as indicated in the centre right diagram)...

---