Spray zone

After being formed as a spray, many of the droplets contain some excess positive (or negative) electric charge. Solvent (S) evaporates from the droplets to form smaller ones until, eventually, ions (MH+, SH+) from the sample M and solvent begins to evaporate to leave even smaller drops and clusters (S H+ n = I, 2, 3, etc,). Later, collisions between ions and molecules (Cl) leave [M + H]" ions, which proceed on into the mass analyzer. Ion yield can be enhanced by including a volatile ionic compound (e.g., ammonium acetate) in the initial solution before it reaches the spraying zone. 

L = residence time of liquid in the froth or spray zone, s... 

Gravity Settlers Gravity can act to remove larger droplets. Set-thng or disengaging space above aerated or boiling liquids in a tank or spray zone in a tower can be very useful. If gas velocity is kept low, all particles with terminal settling velocities (see Sec. 6) above the gas... 

In the tidal zone and the spray zone (known as the splash zone), cathodic protection is generally not very effective. Here thick coatings or sheathing with corrosion-resistance materials (e.g., based on NiCu) are necessary to prevent corrosion attack [4]. The coatings are severely mechanically stressed and must be so formed that repair is possible even under spray conditions. Their stability against cathodic polarization (see Section 17.2), marine growths, UV rays and seawater must be ensured [4,5]. 

The second case assumed kl = 1. The rationale for using this form for Eq. (7) comes from the observation that in conventional spouted beds, used by Liu and Litster (1993a), the times for particles of different mass to circulate through the spray zone were not the same. In fact, Robinson and Waldie (1978) found that for a conventional spouted bed ... 

If we consider different particles, we can see from Eq. (11) that the variation in the total amount of material deposited on each particle is a function of the number of times the particle passes through the spray zone, TV and the amount of material that it receives in each pass, x. Since both x and N vary, we expect that Xlolal will vary between particles in the same batch. Mann (1974) has shown that for a batch coating process in which the operating time is greater than about 20 times the average circulation time,... 

Figure 7. Sheltering effect of particles in the spray zone of a fluidized bed coater.

In general, different sized particles may have different cycle time distributions and different mass deposition distributions in the spray zone. One approach would be to use small discrete size distribution increments and then to apply Eq. (12) to each size fraction. Inherent in this approach is the assumption that each particle size fraction acts independently. This assumption may not be valid, especially if different particles take different circulation paths within the bed. From the population balance approach, Randolf and Larson (1988) have suggested the use of an effective growth diffusivity coefficient to account for random fluctuations in growth rate. Thus Eq. (6) would be modified to give ... 

It is far from certain that such a high-voidage spray zone can exist within a fluidized bed a spray zone, with a submerged nozzle, would require a jet to be blown in the dense phase by the atomising air. Work by Rowe et al. (1979) and by Smith and Nienow (1982), using X-ray... 

Number of spray guns to be used In any film-coating process, it is critical to ensure that the spray zone is optimized with respect to these key criteria ... 

Making sure that the full width of the tablet bed is covered so that few, if any, tablets on the surface pass through the spray zone without receiving some coating... 

A special nozzle surround keeps product further away from the nozzle tip, thus preventing that product from being drawn into the wet area of the spray zone, and also limits the attritional effects that normally accompany the use of high atomizing air pressures and velocities. 

Residues of fenitrothion in fathead minnows were reported by Malls and Muir (19) following treatment of small ponds. Bioconcentration factors were 42 and 54 at 24 hours post treatment, as compared with predicted steady state bioconcentration factors of 146 (Table I). Following actual forest spraying Lockhart et al. (20) reported 13.7 pg fenitrothion per gram in fish taken from a stagnant pond in the spray zone. The peak water concentration observed was 75.5 pg/L, and so the bioconcentration factor was at least 180. Similarly, Lockhart et al. (21) found maximum fish residues of 4.28 pg/g from the same area sprayed two years later, and in this case the peak water concentration was 22.8 pg/L, with a calculated bioconcentration factor of 190. 

The principle public concern with regard to risk from herbicide application in the forest is not the overt, or occupational, exposure to pesticide applicators or to persons who might be in the spray zone. It is the possible injury from pesticide drift at a distance of a few hundred yards or a quarter of a mile, up to 5 to 20 miles. All aerially-applied pesticides will drift for some distance, whether they be applied by fixed-wing craft or helicopter. 

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