Knowing the amount and required characteristics of the pesticide application, we then 
can devise a method of forming the particles required, as well as transporting them to 
and depositing them on the plant. Finally, we are concerned if the particles will adhere 
to the plant they are deposited upon. 
Particle Formation. It is anaxiom of engineering that to control the process you must 
understand the mechanics of the process, and preferably be able to describe it quantita- 
tively. A considerable amount of research has been done on the mechanics of droplet 
formation yet much remains unknown. It is customary to speak of 3 or 4 different modes 
of droplet formation. The first is known as dribble where liquid issues very slowly from 
an orifice and drops are formed one at a time as liquid is supplied to the orifice, such 
as on a burette or pipette. Weunderstandthis process quite well-and can predict and con- 
trol the size of drops which result. As you can easily imagine this process is of little 
usefulness in practical application of chemicals. 
The second mode of droplet formation is known as Rayleigh breakup. In this process 
the liquid issues from a nozzle in a solid jet at relatively low speed, but at some distance 
from the nozzle the liquid jet, because of its inherent instability, breaks up to form 
droplets. Again we understand, can predict and can control the size of droplets formed 
by this process, but it has not been very useful in field application of chemicals. 
The third mode is known as sinuous breakup. At these velocities the liquid jet tends 
to describe a spiral or sinuous path as it issues from the nozzle and because of aero- 
dynamic forces on the jet it breaks up quite quickly. This process is not well understood 
but again it is not very useful in pesticide application because of limited discharge ca- 
pacities. 
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