Electrostatic Spraying of Oil-Based Agricultural Products

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Abstract
There is burgeoning interest in the use of oil based, high-persistence media for the low volume application of agricultural chemicals. Although electrostatic atomizers appear to offer the most appropriate means for the effective application of these carriers, it has heretofore been necessary to modify the formulations to permit operation with existing devices. This has entailed altering the intrinsically high resistivity of these fluids (0.1 cu) to the 104 to 106 cu range where existing electrostatic atomizers can function. A prototype electrostatic atomizer which is capable of spraying unaltered oil-based fluids is described. This device uses direct charge injection to provide unipolarly charged droplet sprays of a wide range of fluids independent of their physical properties. Atomization is purely electrostatic with no auxiliary means such as spinning disks, air blast, or swirl assist being required for droplet formation. A compact device (1 by 2 by 1 in.) is capable of providing flow rates from 0.1 gal/h upwards with constant output charge density. Operation is at about 10 kV and several microamperes for a total electrical input (exclusive of fluid delivery power) of a few tens of milliwatts. This makes the unit compatible with battery operated hand-held as well as power limited mobile applications. Operating characteristics and droplet size distribution data are presented for a representative test oil. It is shown that droplet size distributions that are considerably more monodisperse than those obtained from conventional atomizers can be readily achieved. This feature, along with the intrinsic “wrap-around” capability of the charged droplets, is a particularly significant attribute for effective application.

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