Electrostatic dissemination techniques

Electrostatic forces can be utilized for the direct dissemination of materials, both liquid and solid. The dissemination of liquids by this means (electrostatic atomization) has been studied extensively. The corresponding dissemination of powders is referred to in the literature but has not received much attention in depth. Dissemination of bulk solids (i.e., consolidated solids as distinguished from powders) by electrostatic means has not been studied and, although it may be technically possible, is probably not feasible. 

A large part of the interest in electrostatic atomization has arisen from two fields of interest combustion of fuel oils and ion propulsion of rockets in space. Work in the latter area has been concerned primarily with atomization at high vacuum (10-8 atm) as in the work of Cohen (C5), Hogan (HI2, 13), Hendricks (H6), Schultz and Branson (S2), and Schultz and Wiech (S3). Graf (G8), Matthews and Mason (M3), Peskin and Raco (P3), Randall, Marshall, and Tschernitz (Rl), and Vonnegut and Neubauer (V4) have been concerned primarily with atomization at atmospheric pressure. Most of the 

Peskin and Raco (P3) have given a theoretical analysis of both ultrasonic and electrostatic atomization from the point of view of liquid instability. They conclude that atomization with low frequency ac will require about twice the field strength as dc but that, by going to high frequency, lower fields are possible with conducting liquids. The value for the critical field for atomization given by these authors for a dc field is, however, smaller than that which would be calculated from Eq. (39) by a factor of (1/32)1/2. This presumably reflects the simplified one-dimensional model used in their derivation. 

Graf (G8) measured the pressure buildup due to electrostatic charging of stationary drops. He found this pressure to be some 30-60% of the value given by Eq. (4), independent of polarity of charge or dielectric constant of the liquid. This factor, which he terms a charging factor, was a function of both geometry and liquid properties. It may also reflect polarization effects that are neglected in Eq. (4). 

Drozin (D7) presents an analysis corresponding to Eq. (4) for a polarizable liquid in the absence of any surface charge. However, he expresses the electrostatic pressure in terms of the electric field inside the drop rather than 

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