Electrostatic atomizing device

This invention relates to an electrostatic atomizing device and a process thereof for the formation of electrostatically charged droplets having an average diameter of less than about 1 millimeter for a liquid having a low conductivity wherein the device includes a cell having a chamber disposed therein, a discharge spray mechanism in communication with the cell, the liquid in the chamber being transported to the discharge spray mechanism and atomized into droplets, and a mechanism for passing a charge through the liquid within the chamber, wherein the charge is sufficient to generate free excess charge in the liquid within the chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electrostatic atomizing device and a process 
thereof for the formation of electrostatically charged droplets having an 
average diameter of less than about 1 millimeter for a liquid having a low 
conductivity, wherein the device includes a cell having a chamber disposed 
therein, a discharge spray means in communication with the cell, the 
liquid in the chamber being transported to the discharge spray means and 
atomized into droplets, and a mechanism for passing a charge through the 
liquid within the chamber, wherein the charge is sufficient to generate 
free excess charge in the liquid within the chamber. 
2. Description of the Prior Art 
The literature is saturated with various types of electrostatic atomizing 
devices which are of limited adaptability due to a number of factors such 
as the inability to be functionally operable in air, the inability to 
atomize low conductivity liquids, and the inability to form droplets 
having an average diameter of less than about 10 microns with commercially 
acceptable flow rates. 
U.S. Pat. No. 3,358,731 is a combustion burner device having a diode type 
electrostatic atomizing device, wherein the charged droplets are attracted 
to a downstream charged surface having a lower electrical potential than 
the atomizing device. This atomizing device produces droplets having large 
diameters. 
U.S. Pat. No. 3,597,668 relates to an electrostatic fuel charging device 
for use with an internal combustion engine, wherein a friction element 
disposed within a cylindrically shaped casing imparts an electrostatic 
charge to a liquid fuel flowing through the casing. 
U.S. Pat. No. 3,167,109 relates to a diode type electrostatic atomizing 
device employing a convective flow of charged air in order to 
electrostatically charge a liquid externally to a liquid supply cell. 
The device of U.S. Pat. No. 2,525,347 is a spray diode. In all instances 
cited electrostatic atomization of fluid occurs from a small radius of 
curvature edge or edges over which the fluid passes. Atomization proceeds 
in response to an electric field established between this edge and the 
object or objects toward which the spray is to be directed. High potential 
voltage is stated as being necessary for operation in conjunction with the 
object, nozzle separation distances noted. Without exception operation is 
at ambient conditions with the interelectrode gap in air. 
This invention differs from the process claimed here in that no claim is 
made with respect to forceable charge injection into the spray fluid. 
Since the spray fluid is charged by charge release from a sharpened 
surface in response to large electric fields developed by large potential 
differences operating over large air gaps, the flow rate is restrained to 
that capable of just forming a thin layer over the sharp edge. This is 
consistent with the absence of the third electrode whose presence within 
the liquid would assure sufficient charge injection to permit large volume 
flow rate spraying. 
U.S. Pat. No. 3,775,193 teaches that a passivating liquid flows thru an 
aperture through which an electrode protrudes. A high intensity electric 
discharge is maintained between this electrode and the metallic surface 
being passivated by the fluid. This operation is typically conducted in a 
vacuum below 10.sup.-4 torr. The discharge between the electrode and 
surface produce atomization of sufficient intensity to reduce droplet size 
below 200 .mu.m. 
Small flows are indicated as being associated with this procedure. The 
presence of only two electrodes, the central spray head electrode and the 
work surface distinguish this invention from the spray head concept of the 
instant invention. The presence of a high intensity electric discharge 
between the head electrode and the work piece noted as being central to 
the methods' mode of operation and to the atomization process indicates 
the principle of operation is functionally distinct from the charge 
injection process of the spray diode. 
U.S. Pat. No. 3,167,109 reveals a coaxial device in which electrostatic 
fields are used to: (1) provide an "electric wind" effect to move air to 
the combustion zone, and (2) produce atomization and spraying of liquid 
fuel into the air preparatory to combustion. Electrostatic atomization of 
fuel occurs from a centrally located supply electrode in response to a 
potential difference that exists between it and another electrode. Air 
moves within the annular space defined by the two electrodes. 
Electrostatic atomization is limited in this device by the maximum electric 
field capable of being sustained across the air gap. This device is 
clearly a spray diode since it lacks an essential electrode immersed in 
the spray fluid. As a consequence its spray performance is limited to low 
flow rates. 
U.S. Pat. No. 3,269,446 teaches that the liquid fuel is supplied to an 
annular manifold from which it flows vertically downward and radially 
outwardly over a conical surface, the lower edge of which is sharp. 
Electrostatic spraying occurs from this edge by action of an electrostatic 
field that exists between the spray cone and an annular coaxially 
positioned ring electrode having a larger diameter, and placed lower than 
the cone. An alternate embodiment of this device replaces the second ring 
electrode by a circular cylindrical screen electrode surrounding the 
centrally located spray cone. A second alternation replaces the cone with 
a horizontal sharp disc having a sharp edge from which spraying occurs to 
the ring electrode. 
In all three instances an air gap exists between the two (and only) 
electrodes responsible for spraying. Consequently the devices are all 
subject to air breakdown effects which limit their capability to spray 
large volumes of low conductivity liquids--the devices are spray 
diodes--being only a pair of electrodes. 
A paper by Tsui and Hendricks (RSI, Vol. 39, August 1969) reveals a coaxial 
device designed to disrupt an otherwise uniform column of liquid into a 
co-linear stream of uniform sized droplets (.about.300 .mu.m diameter). 
This is accomplished by positioning a pointed rod coaxially with the exit 
hole through which the liquid flows. Imposition of an alternating voltage 
differential between the pointed electrode and the orifice plate produces 
the desired disruption, but only in a well defined frequency range. 
The alternating voltage is used solely as an oscillating 
electrohydrodynamical pressure source. It is this periodically varied 
pressure that produces the desired breakup. This device does not suggest a 
means for developing spray clouds of small droplets as in the spray 
triode. The Tsui/Hendricks paper, therefore, is non-applicable to the 
Spray Triode of the instant application. 
Paint spraying at elevated voltages (70 KV to 100 KV), as seen in U.S. Pat. 
No. 3,512,502, is produced by rotating a sharp edged truncated cone 
maintained at high potential with respect to the grounded object to be 
coated. Paint is fed to the inside of the spray cone and is atomized as it 
leaves the sharp forward lip. Atomization proceeds by a combination of 
centrifugal and electrostatic forces. 
A third electrode in the form of a small pointed cone is centrally located, 
i.e. is coaxially positioned and is approximately co-planar with the spray 
lip. A resistor is used to maintain this tip at a potential intermediate 
with respect to the spray cone and the grounded target. The device is a 
true Triode, the first thus far identified as prior art. However, a clear 
distinction between this device and the Spray Triode can be made insofar 
as the central third electrode is expressly used to control spray pattern 
geometry by altering the electrostatic field in the vicinity of the spray 
lip. Moreover, the central electrode is separated by an air gap from the 
spray lip. The conical third electrode does not contact the spray liquid 
directly as is the case in the instant application and contact is noted as 
to be avoided for correct operation. 
The spray coating apparatus as seen in U.S. Pat. No. 3,700,168 is a coaxial 
device. Grounded spray liquid is radially flowed outward from a central 
supply tube toward a concentrically positioned electrode. High voltage is 
supplied to this electrode via a current limiting resistor. An air flow is 
maintained in the annular space between the inner liquid supply tube and 
the outer electrode support tube. The air flow, normal to the radially 
directed liquid flow, produces atomization and prevents collection of 
liquid on the high voltage electrode. It is stressed that collection of 
liquid on this electrode is deleterious to proper operation. This is 
clearly a diode, since the target is also at ground potential. 
However, a coaxial, electrically floating cylinder has also been included 
in the description. It is the purpose of this cylinder to provide an 
electric field component to force the spray droplets out of the spray head 
which is encased in a cylindrical grounded enclosure. The patent proceeds 
to elaborate on this "driving" electrode and described a unique design 
that can be added to the gun to improve its spray pattern. 
In place of the electrically floating cylinder a "driving" electrode 
charged to high potential by air-ion collection is detailed. The unique 
feature of this concept resides in the use of feed air stream kinetic 
energy to forcibly convert air-ions to the "driving" electrode. The 
kinetic energy of the air stream overcomes the retarding field of the 
"driving" electrode permitting high potentials to be attained at modest 
operating voltages. The "driving" electrodes is, therefore, charged by the 
equivalent of an air driven Van de Graaf generator. 
Again the use of supplemental means for atomization, lack of emission from 
the electrode, and the absence of direct, forcible charge injection 
clearly distinguishes this device from the Spray Triode of the instant 
application. 
A spray coating apparatus as seen in U.S. Pat. No. 3,587,967 is a Spray 
Diode. In addition, air is used to augment the atomization process. This 
device has coaxial geometry and uses a centrally positioned, sharply 
pointed high voltage electrode. Since the electrode is in air or in an 
air, droplet mixture, its function is not similar to the Spary Triode 
emitting electrode, therefore it cannot be cited as prior art. 
The spray charging device as seen in U.S. Pat. No. 3,698,635 is a spray 
diode by virtue of the fact that two of the three electrodes used are at 
the same potential. In particular, the liquid feed tube and the target are 
both grounded. Liquid is fed through the innermost of three coaxial tubes. 
This feed tube is a dielectric in which a grounded electrode makes contack 
with the conductive spray fluid upstream from the liquid exit position. 
The liquid is forced radially outward from the end of the tubes. An 
enclosing concentric tube, also of dielectric material, supports a high 
voltage electrode coaxially in the vicinity of the liquid exit slot. This 
electrode is connected via a current limiting resistor to a high voltage 
supply. As liquid exits the inner tube, it is atomized partially by action 
of the electrostatic field produced by the high voltage electrode on the 
conducting spray fluid. Atomization is augmented by a high volumetric flow 
rate of air in the annular space defined by the two tubes. Liquid 
reisitivities as high as 1.3.times.10.sup.4 ohmm are quoted as being 
sprayed by this device, a claim is made for 1.5.times.10.sup.5 ohmm as the 
maximum resistivity level. The air flow is noted as being 10.sup.3 times 
that of the liquid. This high flow rates assures atomization and prevents 
liquid from accumulating on the high voltage electrode. Liquid contact 
with this electrode is noted as being inimical to optimal performance. The 
operation of this device is at 4 to 7 KV with an annular gap spacing of 
about 1/2 mm. The entire unit is enclosed in an open-ended grounded 
metallic cone. A second version of this device is also described. In this 
version liquid is coaxially flowed out of a 1.52 mm ID nozzle on the 
centerline. The end of this tubular nozzle is coaxial with a high voltage 
electrode and separated from it by an annular gap of .about.0.9 mm through 
which air is forced. The indicated liquid flow rates were 0.83 to 4.67 
ml/Sec with air flow again about three orders of magnitude higher (1420 
ml/Sec). Indicated mean charge to mass ratios of 4.2.times.10.sup.-3 C/kg 
at 0.83 ml/Sec and 2.0.times.10.sup.-3 C/kg at 4.67 ml/Sec for this device 
place it in precisely the same performance category as the present 
apparatus. It should be noted that the instant invention attains the same 
charge levels but with a fluid some 10.sup.9 times more resistive and 
without need of an air flow. This spray unit is non-applicable to our 
patent application. It is noted that a third electrode can be added 
coaxially with the device and at its exit. It is the purpose of this 
electrode to help shape the spray geometry, i.e. to concentrate it in the 
forward direction. With this electrode in place, the unit is a spray 
triode but of the same type as represented in U.S. Pat. No. 3,512,502. 
SUMMARY OF THE INVENTION 
This invention relates to an electrostatic charging device and a process 
thereof for the formation of electrostatic charged droplets having an 
average diameter of less than about 1 millimeter for a liquid having a 
conductivity of less than about 10.sup.4 mho/meter, more preferably less 
than about 10.sup.-4 mho/m, most preferably less than about 10.sup.-10 
mho/m, wherein the device includes a cell having a chamber disposed 
therein, a discharge spray means in communication with the cell, the 
liquid in the chamber being transported to the discharge spray means and 
atomized into droplets, and a mechanism for passing a free excess charge 
through the liquid within the chamber sufficient to generate free excess 
charge in the liquid within the chamber. 
GENERAL DESCRIPTION 
The electrostatic charging device of the instant invention includes a cell 
having a chamber therein with a discharge spray means disposed at one end 
of the cell, wherein the liquid to be atomized is disposed within the 
chamber and is emitted as charged particles from the discharge spray 
means. A charge which is sufficient to generate a free excess charge in 
the liquid is passed through the liquid within the chamber. The convective 
flow velocity of the liquid within the chamber is the same or different 
than the mobility controlled current flow velocity within the chamber 
thereby permitting the excess free energy charge to be effectively 
transported to the discharge spray means. 
The current source usable for producing the charge means within the chamber 
of the cell can be a direct voltage, an alternating voltage, or a pulsed 
voltage source and mixtures thereof of about 100 volts to about 100 
kilovolts, more preferably about 100 volts to about 50 kilovolts DC, most 
preferably about 100 volts to about 30 kilovolts DC. The charge induced 
into the liquid within the cell can be colinear or at an angle of 
intersection to the convective flow velocity of the liquid within the 
chamber, wherein the convective flow velocity of the liquid can be less 
than, equal to, or greater than the mobility controlled current flow 
velocity of the charge within the cell. The induced electrical charge 
introduced into the liquid within the cell must be sufficient to generate 
free excess charge in the liquid within the chamber, wherein the charge 
can be negative or positive. 
The formed droplets exiting from the discharge spray means can be 
accelerated outwardly from the discharge spray means without any 
substantial stagnation, or emitted from the discharge spray means in a 
swirl configuration, or emitted from the discharge spray means in a planar 
configuration. The formation of the charged droplets can occur either 
within the spray discharge means or externally thereto. 
Heating or cooling means can be provided for controlling the viscosity of 
liquid within the chamber of the cell, wherein the heating or cooling 
means can be a jacketed cell having a heated liquid oil or a refrigerant 
liquid disposed therein, or alternatively for the heat means convective 
hot air can be impinged on the cell or electrical heating elements 
embedded in the wall of the cell or disposed within the liquid within the 
chamber of the cell. The control of the viscosity of the liquid within the 
chamber of the cell could permit a wide range of materials to be employed 
as well as a means for controlling the flow rates of the liquids. 
Solutions of non-conductive liquids with solids or gases dispersed therein 
could be readily employed. A liquid pump means could be joined in a serial 
fluid communication to the cell for the creation of a positive pressure on 
the liquid within the cell thereby providing a means for the regulation of 
the flow rate. 
A supply tank can be joined in a serial fluid communication to the 
electrostatic atomizing device by means of a conduit having a metering 
valve disposed therein. 
A cleaning solution such as aromatic, cycloaliphatic, aliphatic, 
halo-aromatic, or halo-aliphatic hydrocarbon could be disposed and stored 
within the supply tank for subsequent atomization into a spray of fine 
droplets for the cleaning of a surface of an article disposed externally 
to the electrostatic atomizing device. For example, a surface of an 
industrial machine or an engine block caked with oil and grease could 
readily be cleaned with this device. 
It is contemplated that an agricultural liquid such as an insecticide or 
protective fog agent could be disposed and stored in the supply tank for 
the subsequent formation into a spray of fine droplets which could be 
directed onto vegetation or soil for insect and pest control. This device 
could be readily mounted to a ground vehicle or even to an airplane for 
air spraying operation. 
A lubrication oil could be readily disposed and stored in the supply tank 
for subsequent formation into a spray of fine droplets which would be 
readily adaptable for oil-mist lubrication of bearings and gears of large 
industrial machinery. 
A solution of a plastic dissolved in a non-conductive liquid or an oil 
based paint could be readily disposed and stored in the supply tank for 
subsequent formation into a spray of droplets for impigment onto the 
surface of an article disposed externally to the discharge spray means 
thereby forming a coating on the surface of the article. 
The present apparatus could be readily used to inject free excess charge 
into a molten plastic glass, or ceramic. If the plastic is rapidly cooled 
and solidified, a highly charged electret would be formed. 
The cell of the electrostatic atomizing device could be joined in a serial 
fluid communication to a conventional plastic extruder, wherein a plastic 
material would be liquified under heat and pressure, transferred into the 
chamber of the cell and subsequently formed into a spray of charged 
droplets impingement of plastic on the surface of an article disposed 
externally to the cell thereby forming a coating on the surface of the 
article. Typical plastic materials could be selected from the group 
consisting of polyethylene, and copolymers thereof, polypropylene, 
polystyrene, nylon, polyvinyl chloride, or cellulose acetate or any other 
extrudable plastic material. Coal so extruded and heated could be atomized 
by this method providing a means to directly burn this material. 
The spray discharge head of the electrostatic atomizing device could be 
disposed within a liquid which is disposed in a container that is 
externally disposed to the electrostatic atomizing device, wherein the 
charged droplets would be formed within the liquid. If a metal object 
which is oppositely charged to the charged droplets was disposed within 
the liquid the charged droplets would migrate through the liquid to form a 
coating on the surface of the metal article. An ideal application would be 
in the painting of metal objects such as automobiles, wherein the charged 
droplets are a paint. 
Two electrostatic atomizing devices could each be joined in a serial fluid 
communication to a mixing vessel, wherein the first device would inject 
positively charged droplets into the mixing vessel and the second device 
would inject negatively charged particles into the mixing vessel thereby 
permitting an intimate mixing and neutralization of the positive and 
negatively charged droplets within the mixing vessel. The mixing of the 
negatively and positively charged particles with the mixing vessel could 
occur either in air or in a liquid disposed within the mixing vessel. 
The charged liquid droplets from the electrostatic atomizing device can be 
readily sprayed onto an oppositely charged powder disposed externally to 
the device, wherein the powder can be disposed under agitation in a 
container or in the fluid bed. The charged droplets are coated onto the 
surface of the powder, wherein a neutralization of charge occurs. A 
typical possible application would be the coating of a perfume onto a 
talcum powder. 
The charged liquid droplets from the electrostatic atomizing device can be 
readily sprayed onto the outer surface of an article which is oppositely 
charged to that of the charge of the droplets thereby causing a decharging 
by neutralization of the charged outer surface of the article. A typical 
example of this type of application would be the spraying of a large 
industrial tank which may have become electrostatically charged. 
Alternatively, the charged droplets could be injected into a liquid within 
the tank for subsequent decharging of the inner surface of the charged 
tank. 
The electrostatic atomizing device could be joined in serial fluid 
communication to a liquid pump means disposed within a hand held aerosol 
generator, and a liquid supply tank would be detachably secured to the 
hand held generator and would be in serial fluid communication with the 
liquid pump means. A magnetoelectric generator means would be disposed 
within the hand held generator, wherein said generator means would 
generate the electrical charge to be induced into the liquid with the 
cell. An activation means such as a trigger assembly would be disposed 
within the hand held device for the simultaneous activation of the 
generator means and the liquid pump means. This assembly could be readily 
employed as a replacement for aerosol cans. 
The difficulty of obtaining efficient combustion of hydrocarbon fuels can 
be readily overcome be decreasing the size of the formed droplets thereby 
providing increased surface area for combustion and consequently improved 
efficiency of heat transfer. The formation of droplets having a diameter 
of about 1 micron to about 1 millimeter, more preferably about 2 to about 
50 microns permits the spray of fuel into the combustion chamber to be 
uniformly dispersed. The electrostatic atomizing device of the present 
invention would be readily adaptable for delivery of a fine spray of 
hydrocarbon fuel such as No. 2 heating oil to the combustion chamber of 
domestic and industrial oil burners. Additionally, the electrostatic 
atomizing device can be charged with gasoline for subsequent atomization 
into a gasoline spray for injection indirectly into an internal combustion 
engine through a carburetor or directly into the head of an internal 
combustion engine such as an Otto, Diesel, or Brayton. These oils and 
gasolines have extremely low ohmic conductivities on the order of about 
10.sup.-13 to about 10 .sup.-6 mho/meter, more preferably about 10.sup.-6 
to about 10.sup.-12 mho/meter most preferably about 10.sup.-8 to about 
10.sup.-12 mho/meter. Heretofore, the ability to atomize these fuels into 
electrostatic charged particles has been limited by the inability to 
effectively create an excess free charge within the liquid thereby 
preventing the formation of particles having a diameter of less than about 
50 microns at commercially acceptable flow rates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now descriptively to the drawings, in which similar reference 
characters denotes similar elements throughout the views of the different 
embodiments, FIGS. 1, 2 show a first preferred embodiment of an 
electrostatic atomizing device 10 which includes a cylindrically shaped 
non-conductive housing (cell) 12 (e.g. Lucite) having a base 14, an 
upwardly extending cylindrically shaped sidewall 16 with a threaded 
aperture 21 therethrough, a top 22 with a threaded aperture 20 
therethrough and a threaded hole 24 therethrough, and a chamber 26 
disposed therein, wherein the base 14 has a center discharge opening 28 
therethrough which is the discharge spray means. One threaded end 30 of a 
first cylindrically shaped liquid supply conduit 32 is threadably received 
into hole 24, wherein the conduit 32 extends linearly outwardly from the 
top 22 of the housing 12. The other threaded end 34 of conduit 32 is 
adapted to be joined to a liquid supply means (not shown) whereby the 
liquid passes through conduit 32 into chamber 26, wherein the liquid has a 
conductivity of less than about 10.sup.4 mho/meter, more preferably less 
than about 10.sup.-4 mho/meter, and most preferably less than about 
10.sup.-10 mho/meter, e.g. No. 2 grade heating oil. A first non-conductive 
elongated cylindrically shaped tube 42 having an externally threaded 
surface 18 and a continuous bore therethrough is threadably disposed 
through threaded aperture 20, wherein one end 46 of tube 42 extends 
outwardly from housing 12 and the other end 48 of tube 42 extends inwardly 
into an upper portion of chamber 26. A first electrode 38 or a series of 
first electrodes 38 in parallel or in a parallel series combination is 
joined into the end 48 of tube 42 by suitable means such as an adhesive 
cement or the end 48 of tube 42 can be embedded into electrode 38, wherein 
electrode 38 has a setaceous surface 50 formed from a plurality of pins 51 
which are in a substantially parallel alignment within the chamber 26. A 
setaceous surface is defined as one having a plurality of essentially 
parallel similar continuous pins having lateral dimensions of order 10 
.mu.m, more preferably1 .mu.m, most preferably 0.1 .mu.m or less in a 
matrix of non-conductor or semi-conductor material. Each pin is arrayed in 
a regular or almost regular pattern with mean separation distances of an 
order of about 35 .mu.m or less. An example of a suitable electrode 38, 
but not limiting in scope, is a eutectic mixture of uranium oxide and 
tungsten fibers as described in Journal of Crystal Growth 13/14, 765, 771 
(1972) "Unidirectional Solidification Behavior in Refractory Oxide Metal 
Systems," A. T. Chapman, R. J. Geides. The first electrode 38 is connected 
in series to a high voltage source 40 which is disposed externally to the 
housing 12, by means of a first electrical lead wire 52 extending through 
the bore 44 of tube 42. The high voltage source 40 is wired by means of a 
ground wire 76 to a ground 78 disposed externally to device 10. A second 
non-conductive e.g. Lucite) elongated cylindrically shaped tube 56 having 
a continuous bore 58 therethrough is disposed through aperture 21, wherein 
one end 60 of tube 56 extends outwardly from housing 12 and the other end 
62 of tube 56 extends inwardly into a lower portion of chamber 26. A 
liquid tight seal is formed between tube 56 and widewall 16 by adhesive or 
other sealant means 54. A second electrode 64 or a series of second 
electrodes 64 in parallel or in series parallel combination are joined 
onto end 64 of tube 56 by suitable means such as an adhesive cement or the 
end 62 of tube 56 can be embedded in electrode 64. The second electrode 64 
is a planar shaped disc 66 having at least one center longitudinally 
aligned aperture 68 therethrough and optionally a plurality more of 
longitudinally aligned apertures 70 therethrough at prescribed distances 
from the center aperture 68; alternately a plurality of longitudinally 
aligned apertures 68 could be used arrayed symmetrically with respect to 
the center line with no aperture hole on the center line. The aperture 
holes could also be skewed to the center line. The second electrode 64 is 
disposed transversely within chamber 26 below and spaced apart from the 
first electrode 38. Electrode 38 can be moved longitudinally upwardly or 
downwardly thereby reducing or increasing the gap between the electrodes 
38, 64 as well as modifying the flow of charge within the liquid. The 
second electrode 64 is preferably formed from platinum, nickel or 
stainless and is wired in series to a high voltage resistor element 72 
disposed externally to housing 12 by an electrical lead wire 74 extending 
through tube 56. The resistor element 72 is connected at its opposite end 
to ground juncture 80 of the high voltage source 40. An external annularly 
shaped electrode 82 (e.g. stainless steel) can be affixed on the external 
bottom surface 84 of base 14 by adhesive means or by a plurality of 
anchoring elements 86 extending upwardly through electrode 82 and being 
embedded into base 14. The center opening 88 of electrode 82 and discharge 
opening 28 are aligned, wherein opening 28 is preferably less than about 2 
cm in diameter, more preferably less than about 1 cm in diameter most 
preferably less than about 6 mm microns in diameter, and the diameter of 
the center opening 88 is less than about 1 mm, more preferably less than 
about 600 .mu.m, and most preferably less than about 200 .mu.m. In this 
position, electrode 82 assists the spraying due to the development of the 
electrostatic field; however, the positioning of electrode 82 at this 
position is not critical to operation as long as this electrode 82 is 
disposed external to housing 12. The electrode 82 is also connected to a 
second grounded junction 90 disposed between ground 78 and the first 
electrical juncture 80. The first electrode 48 is negatively charged 
wherein the second electrode 64 has a relative positive potential with 
respect to the first electrode 38 and the external electrode 82 is at 
ground potential (the positive potential of source 40). In one mode of 
operation the first electrode 38 is negatively charged at the second 
electrode 64 and the external electrode 82 are relatively positively 
charged. The high voltage source 40 which can be a direct voltage, an 
alternating voltage, or a pulsed voltage source of either polarity, 
wherein the source is about 100 volts to about 100 kilovolts, more 
preferably about 100 volts to about 50 kilovolts DC, and most preferably 
about 100 volts to about 30 kilovolts DC. The charge induced into the 
liquid 36 within the chamber 26 results in a flow from the first electrode 
38 to the second electrode 64. The liquid within the chamber 26 flows 
towards the discharge opening 28 of the base 14, wherein the electrical 
charge which is induced into the liquid within the chamber 26 must be 
sufficient to generate excess free charge in the liquid within the chamber 
26, wherein the charge can be positive or negative. The liquid is emitted 
outwardly thereform in a spray configuration, (as a plurality of droplets 
92), wherein the external electrode 82 enhances acceleration of the 
charged droplets 92. 
FIG. 3 shows the electrostatic atomizing device 10 in a serial fluid 
connection to a supply means 108 which includes a tank 110 having a base 
112, a plurality of upwardly extending walls 114, a top 116 with a 
threaded opening 120 therein, and a chamber 122 therein, wherein the 
liquid to be atomized is stored within chamber 122. One end 124 of a 
second cylindrically shaped liquid supply conduit 126 extends through one 
of the walls 114 of tank 110. The other end 128 of conduit 126 and the 
other end 130 of conduit 32 are joined in a serial fluid communication to 
a liquid valve means 132. A plurality of wheel members 134 can be affixed 
to the base 112 of tank 110 thereby improving mobility of the device 10. 
FIG. 4 illustrates the electrostatic atomizing device 10 disposed in the 
chamber 134 of a cylindrically shaped combustion burner device 136 having 
an open end 138 a cylindrically shaped sidewall 140, and a top 142, 
wherein conduit 32 extends through top 142 and the spray of droplets 92 
formed within chamber 134 are mixed with air and subsequently ignited with 
the combustion zone of the chamber 134 by means of a suitable igniting 
means 135 such as a spark plug. The air is supplied into chamber 134 by 
standard fan or compressor means. The sidewall 140 can also have a 
plurality of air inlet apertures 13 therethrough for supplemental 
injection of air into chamber 134. 
FIG. 5 shows the electrostatic charging device 10 joined in communication 
with a hand activating device 240. The hand activating device 240 includes 
a cylindrically shaped housing 242 of an L shaped configuration having 
shorter 244 and a longer 246 legs, wherein the open end 248 of the longer 
leg 246 is internally threaded and is adaptable for threadably receiving 
the externally threaded neck 250 of a bottle 252 having a vent 251 therein 
which is adapted for receiving liquid 36 therein. The closed end 254 of 
the shorter 244 has an opening 256 therethrough, wherein the device 10 of 
the first embodiment as depicted in FIGS. 1, 2, 6 or 7 extends 
therethrough with the discharge opening 28 of device 10 being disposed 
externally to housing 242. The end 34 of conduit 32 is joined in serial 
fluid communication with a liquid pump means 256 disposed within housing 
242 at the juncture 258 of legs 242, 246. One end 260 of elongated liquid 
supply conduit 262 is in serial fluid communication with liquid pump means 
256, wherein conduit 262 extends linearly through leg 246 with the other 
end 264 extending outwardly from open end 248 and adapted to be recieved 
into the liquid 36 disposed in bottle 252. A bore conductive tigger means 
266 extends through the sidewall 268 of leg 244 wherein the tigger means 
266 is disposed on a pin 270 are journalled for rotation in the inner 
surface of sidewall 268 of leg 244. The inner end 272 of tigger means 266 
is joined to the stem rod 280 of the piston 282 of liquid pump means 256. 
A magnetoelectric generator means 284 with a drive shaft 287 is disposed 
with chamber 272 of housing 242, a pinion gear 285 is disposed on shaft 
287. A rack gear 289 is joined to tigger 266 and meshes with gear 287 such 
that movement of tigger 266 causes activation of generator means 284. The 
generator means 284 functions as the high voltage source 40 of the device 
10 as depicted in FIGS. 1, 2, 6, or 7. A return spring member 286 
communicates between the tigger means 266 and an anchor element 288 
disposed on the inner surface of sidewall 268 of leg 244. In operation, 
when the tigger means 266 is activated pump means 256 pumps liquid 36 into 
chamber 26 of device 10 as the electromagneto means 284 delivers a high 
voltage current to the first electrode 38. 
FIG. 6 shows a second embodiment of the electrostatic charging device 10, 
wherein the modification from the first embodiment of device 10, includes 
the design and positioning of first 38 and second 64 electrodes within the 
chamber 26. The first electrode 38 includes a cylindrically shaped 
conductive plug 204 having a longitudinally extending bore 206 
therethrough, wherein bore 206 extends from an upper 208 to a lower end 
210 of plug 204. The surface 211 of bore 206 is formed from a plurality of 
sharp-edged longitudinally, close-spaced riges 212. The second electrode 
64 is an elongated cylindrically shaped member 216 disposed within the 
bore 206 of plug 204, wherein tube 56 affixed linearly to one end 214 of 
member 216 extends linearly upwardly through a liquid tight aperture 218 
within top 22 of device 10. The plug 204 can be formed from a plurality of 
razor blades stacked and adhesively secured together in the desired 
cylindrical shape. The outer cylindrically shaped sidewall 220 of plug 204 
is secured by adhesive means 222 to the inner cylindrically shaped surface 
of sidewall 16 of housing 12 thereby causing the liquid disposed within 
the chamber 26 to flow downwardly through the annular gap 224 defined by 
bore 206 and member 216. The flow of charge between the electrodes 38, 64 
is perpendicularly to convective flow of liquid within the annular gap 
224. 
FIG. 7 shows a third embodiment of the electrostatic charging device 10, 
whereby the modification from the first embodiment of device 10 includes 
the positioning and design of the first 38 and second 64 electrodes within 
the chamber 26. The first electrode 38 consists of an elongated rod 223 
with a sharp tipped end 221, wherein rod 223 extends transversely through 
the sidewall 16 of housing 12. Tube 46 is joined to electrode 64 and tube 
46 extends through an opening 230 in sidewall 16 of housing 12 and is 
adhesively secured therein, wherein the blunt face 63 of electrode 64 is 
longitudinally aligned within chamber 26. Rod 223 can be moved so as to 
adjust the gap between surface 221 of electrode 38 and electrode 64 within 
the chamber 26. The end 221 of the first electrode 38 is disposed within 
chamber 26 and is disposed transversely across from electrode 64 within 
chamber 26. Depending on the positioning of the first electrode 38 
relative to the stationary second electrode 38 within the chamber 26, the 
gap distance between the electrodes 38, 64 can be readily varied as well 
as the angle of intersection of the flow charge within the chamber 26 
relative to the flow of liquid 36 within the chamber 26. Alternatively, it 
is fully contemplated within the scope and spirit of the invention that 
the second electrode 64 can be made longitudinally movable within the 
chamber 26. 
EXPERIMENTAL RESULTS OF THE VARIOUS PREFERRED EMBODIMENTS OF THE INVENTION 
The following examples are intended to provide sufficient experimental data 
for a complete understanding of the instant invention but is not to be 
construed as eithr limiting the spirit or scope of the invention. 
EXAMPLE 1 
An extensive series of tests involving Spray Triode configurations similar 
to that depicted in FIGS. 1, 2 were conducted. The purpose of these tests 
were two-fold: 
1. To map the terminal characteristics of Spray Triode operation as a 
function of internal geometry, flow rate, voltage and resistance level, 
and 
2. To maximize mean specific charge (mean spray charge to mass ratio), i.e. 
to minimize mean spray droplet size. 
Negative high voltage was applied to the centrally located emitting 
electrode 38 (FIG. 2). Electrode 38 was movable along its axis permitting 
its relative position with respect to the blunt electrode 64. 
For the majority of tests electrode 38 consisted of a 3 mm diameter 
stainless steel rod surmounted by a 2 mm thick segment of uranium oxide, 
tungsten composite setaceous surface. The terminal end 50 to which the 
uranium oxide tungsten emitting surface was brazed, was ground to a 
conical configuration whose axis was coincident with the centerline of the 
stainless steel support stem and the device proper. Total included cone 
angles of from 120.degree. to 60.degree. were successfully operated. The 
data to be discussed were collected with a 60.degree. C. one corresponding 
to an emitting surface (the setaceous surface) having a conical base 
diameter of 1.5 mm and a height of 1.1 mm. The setaceous electrode 
material in this test sequence had .about.2.multidot.10.sup.7 tungsten 
pins each 1/2 .mu.m in lateral extent, oriented parallel to the stem 
centerline and distributed uniformly and almost regularly across the 
surface. 
The presence of small conducting pins served to enhance the local electric 
field in the pin's immediate vicinity and to facilitate charge emission 
from the metal into the spray fluid. The setaceous surface so acted as a 
field emitter of negative charge under action of the electric field 
developed by the voltage differential applied between this electrode 38 
and the blunt electrode 64. Initial operation was obtained with etched, 
free standing tungsten pins. Etching preferentially removed the uranium 
oxide matrix exposing the tungsten single crystal pins. These pins 51 were 
about 5 .mu.m long and were selectively etched to sharp points at their 
terminal ends. It was the purpose of this sharpening process to enhance 
the electric field magnification factor at the pin tips. 
Electric field enhancement at the emitting tips is a characteristic feature 
of Spray Triode operation. Electric field enhancement due to small radius 
of curvature emitting regions permits the development of high field 
strenghts at the emitter pins while maintaining a very much lower electric 
field strength in the bulk of the fluid in the interelectrode gap. In this 
way, when sufficient voltage is applied to cause field emission from the 
surface the free electrons are released into a region in which their 
mobility velocity is low in accordance with the low interelectrode field 
strength. 
Spray Triode operation for periods of .about.1/2 hour was found to 
effectively erode the pins 51, leaving short nubs (1 .mu.m) or in some 
instances removing the tungsten to positions below the mean surface of the 
electrode. Despite this no gross degradation of Spray Triode operating 
behavior was observed during the course of this reduction process. For all 
intents and purposes, the shortened pins 51, because of their small 
lateral dimensions, produced field enhancement comparable to their 
initial, elegantly sharpened configuration. On the basis of this 
observation, the bulk of testing was conducted with ground and polished 
composite structures. No subsequent provision was made to provide free 
standing pins. Operation of individual examples of composite, setaceous 
emitting surfaces for tens of hours revealed no pattern of degradation, 
with day to day reprocibility of 10% typical. 
A variety of blunt electrodes 64 were used during the course of this work. 
Typically, these electrodes were fabricated from 250 .mu.m thick (0.010"), 
304 stainless steel sheet. The detailed results to be discussed were 
obtained with a blunt electrode having a single 200 .mu.m diameter 
(0.008") hole 68 concentrically placed with respect to the emitting 
electrode centerline. The blunt electrode 54 was connected to ground via a 
high resistance (R) 72. The majority of tests were conducted with a 1000 
meg .OMEGA. resistor. Other resistance values up to 5000 meg .OMEGA. were 
tested and provided acceptable operation. Multihole blunt electrodes 64 
were tested and worked well. In particular, three 200 .mu.m holes 
equi-spaced 500 .mu.m apart and four 156 .mu.m holes in a 250 .mu.m square 
pattern were successfully run. 
Both the emitting electrode 38 and the blunt electrode 64 were mounted in a 
lucite head 31.8 mm in outside diameter and 11.51 mm in inside diameter. 
Various inserts 11.46 mm outside diameter, 65.3 mm inside diameter were 
used to vary the amount of swirl imparted to the spray fluid as it entered 
the Spray Triode from two diametrically opposed entrances provided for 
this purpose. The presence of swirl did not significantly alter the 
electrical characteristics of the Spray Triode. It did, however, provide 
enhanced fluid disruption in the absence of an impressed electric field 
and, therefore, will be of importance for applications where droplet 
generation in the absence of applied voltage is important. 
In the tests to be described, a no-swirl insert having radial passages 
connecting the inlet ports to the interelectrode charge injection volume 
was employed. The resultant exit stream from the 200 .mu.m diameter exit 
port hole 68 in blunt electrode 64 had a glassy, rod-like appearance with 
occasional breakup into a co-linear stream of droplets 200 .mu.m in 
diameter occurring .about.10 cm downstream of the blunt electrode. This 
breakup occurred under the action of random mechanical vibration which was 
intermittantly present in the test apparatus. 
The third electrode 82, was electrically connected to a cylindrical 
collection receptacle configured and positioned to intercept all of the 
dispersed spray. Both 82 and the collection electrode formed a single unit 
electrically--at ground potential. 
Terminal behavior of the Spray Triode device, i.e. current to the emitting 
electrode 38 and from the blunt electrode 64 and collector electrode 84 as 
a function of impressed voltage (V.sub.a) for various electrode gap 
spacing(s) and flow rates Q were obtained. A small gear pump capable of 
supplying up to 10 ml/Sec at pressures up to 1000 KPa was used in 
conjunction with filters (10-13 .mu.m), an accumulator to smooth pump 
induced pressure pulsations, ball float flow meters to monitor flow rate 
and suitable valves to provide control comprised the flow system used to 
circulate the spray fluid during testing. 
In all instances, a highly refined paraffinic white oil was used in the 
tests. This oil, Marcol 87, is defined in Table I. 
Continued use of the same oil for extended periods of time (months) 
resulted in very modest alteration of the physical properties from those 
noted in the table for fresh oil. After about two months of daily 
operation ohmic conductivity was found to have increased from 
0.3.times.10.sup.-12 mho/m to 0.9.times.10.sup.-12 mho/m. When tested 
after 6 months of operation ohmic conductivity had increased to 
1.6.times.10.sup.-12 mho/m. In all instances, these values of ohmic 
conductivity were deemed sufficiently low as to permit neglect of the 
observed temporal variation. 
Testing was conducted in a cylindrical (35 cm diameter) enclosure purged 
with a continuous stream of nitrogen. To obviate the possibility of 
inadvertent droplet spray combustion, the enclosure oxygen content was 
maintained below 5% for all testing. 
Spray Triode operation with a combinaton of DC voltage plus a variable AC 
component revealed that under all conditions studied (alternating voltages 
having frequencies in the range 15 to 1200 Hz and amplitudes up to the DC 
level .about.10KV) poorer charge injection and lowered mean specific 
charge, as compared to DC performance, resulted. Consequently, all testing 
was conducted using a DC power supply. A NJE general purpose 0 to 30 KV 
high voltage power supply was used for all tests. Two 0.02 .mu.f high 
voltage capacitors in parallel were used to reduce ripple at operating 
voltage from .about.80 V P-P to .about.10 V P-P. 
Additional tests conducted on this embodiment were designed to: (1) 
optimize Spray Triode performance (i.e. maximize mean observed specific 
charge), and (2) develop a data base from which a detailed understanding 
of Spray Triode operation could be developed. 
Volumetric flow rate (Q), A-B electrode spacing(s) and applied voltage 
(V.sub.a) were systematically varied during these tests. Operating 
temperature was fixed at 25.+-.1/2.degree.0 C. With the exception of one 
test sequence conducted using a 5.times.10.sup.9 resistor 72 between the 
blunt electrode 64 and ground 79 all data were otherwise obtained with a 
10.sup.9 value for this resistor 72. No measurable dependence of spray 
behavior upon resistance level, in the range noted, was observed. This was 
taken as justification for the elimination of this parameter from detailed 
study. 
In accordance with Ostroumov's observation that for laminal flow (a 
situation that exists in this experiment) field emitted space charge 
limited current is cubically dependent upon impressed voltage 
differential, all data were plotted as I.sup.1/3 vs. voltage differential. 
A cubically related I,V characteristic would plot as a straight line. 
Graph I represents one set of data obtained at a fixed flow rate of 1.05 
ml/Sec. A separate curve is present for each of the three interelectrode 
gap spacings tested. A similar set of data was obtained for each of the 
four flow rates studied (0.43, 0.60, 0.83 and 1.05 ml/Sec). 
The bi-linear behavior of the data is readily apparent. This is a feature 
exhibited by the Spray-Triode at all flow rates tested, when using 
UO.sub.2 /W setaceous emitting electrodes. Within experimental error of 
.noteq.10% current (.about..+-.3% in I.sup.1/3), the data are linear, i.e. 
current is cubically dependent upon voltage, both below and above the 
breakpoint. Data obtained at voltage above the breakpoint are somewhat 
more scattered than that at lower voltages, but are consistent with a 
cubical I,V relatinship. 
The data can be correlated in terms of space change free electric field 
strength at the emitting electrode tip. Using the derivation of Jones for 
electric field strength in the vicinity of a hyperboidal point the data 
support interpretation of emission occurring from a 34 .mu.m radius region 
on the electrode centerline. This is consistent with the observed tip 
geometry after a period of operation wherein the initially sharply pointed 
conical tip has been eroded to a stable, equilibrium configuration (cone 
plus hemispherical cap). Use of this value for tip radius and the 
relationship presented by Jones permitted the voltage differential to be 
interpreted in terms of tip electric field strength. The data of Graph I 
have been replotted in terms of tip field strength as shown in Graph II. 
The three data curves of Graph I obtained at various interelectrode gap 
spacings, have coalesced into a single curve on the I.sup.1/3 vs. -E plot 
(-E=10.sup.-7 .times.E.sub.TIP). Again the cubical nature of the emission 
behavior is clearly evident. A feature common to all I.sup.1/3 vs. -E 
plots independent of flow rate. 
Similar behavior is exhibited by the data when plotted as *(Q/M).sup.1/3 
vs. -E cf Graph III. Not unexpectedly the data support a bimodel cubical 
dependence of observed means specific charge on applied emitter tip field 
(and/or voltage differential). 
The breakpoint, defined as the intersection of the two linear portions of 
the (I.sub.b +I.sub.c).sup.1/3 vs. [-(V.sub.a -V.sub.b)], (I.sub.b 
+I.sub.c).sup.1/3 vs. -E.sub.TIP or *(Q/m).sup.1/3 vs. E.sub.TIP, within 
the limits of experimental error, occurs at the value of voltage 
differential (or equivalently the space charge field free electric field 
at the emitting tip) where measurable current is first observed from the 
blunt electrode. For voltages below the breakpoint current from the blunt 
electrode (I.sub.b) is in the noise level of the experiment, i.e. &lt;1na. 
FNT *Note: I.sub.c/m =Q/M 
Above the breakpoint I.sub.b was found to depend cubically on voltage 
differential. The blunt electrode 64 collected current under all test 
conditions accounted for less than 26% of the total emitted current. 
Analysis of the least square fit straight lines through the (I.sub.b 
+I.sub.c).sup.1/3 vs. -E data revealed the following correlations: 
1. Slopes of the initial, low voltage lines decreased modestly with 
increasing flow rate. However, the slopes for all flow rates studied were 
equal to 1.45.times.10.sup.4 AMP.sup.1/3 /V/m with a standard deviation of 
4.3%. 
2. Closely similar behavior was exhibited by the slopes of lines 
correlating the data taken at voltages above the breakpoint. 3. The slopes 
of the two linear portions of a given data set taken as fixed flow rate 
were found to be correlated. The ratio of the initial to high voltage 
slopes equal 1.935 with a standard deviation of 3.0%. No correlation with 
either flow rate or gap spacing was observed. 
Analysis of the maximum attainable electric field strength (computed as 
space charge free) at the emitting tip (i.e. the electric field strength 
corresponding to the highest sustainable voltage differential in the 
absence of breakdown) revealed a linear dependence on flow rates (Q, 
ml/Sec), viz, E.sub.TIP /max.=-(6.89+8.59 Q).times.10.sup.7 V/M, with a 
coefficient of determination, r.sup.2 =0.966. Within experimental error 
this relation is independent of gap spacing over the range studied 
indicating fluid velocity and fluid properties are the sole factors 
influencing maximum sustainable electric stress. The higher the velocity 
in the emitting tips vicinity the higher the maximum electric field. 
For all data collected the breakpoint electric field E.sub.b was found to 
be a fixed fraction of the maximum sustainable electric field. The 
existence of a fixed proportionality (0.52 with a standard deviation of 
8.5%) indicates a common mechanism exists underlying the behavior of Spray 
Triode operation. 
A model of Spray Triode operation can be inferred from these data. As the 
voltage differential is increased (at fixed gap spacing and flow rate) 
emission starts to occur at the emitter electrode 38 tip. Free electrons 
are injected into the spray fluid. Upon leaving the immediate vicinity of 
the emitting pins 51 in the setaceous surface 50 of electrode 38 the 
electrons, whether attached or free or intermittantly bound, start to 
drift toward the blunt electrode 64. Drift velocity is controlled by the 
electronic mobility m and the mean electric field in the (38)-(64) gap 
region. 
During low voltage differential charge injection the bulk fluid velocity is 
sufficiently high to prevent the injected charge from reaching the blunt 
electrode. Coaxial placement of the emitter electrode and emission from 
the tip region insures that the freed charge will be introduced into the 
high velocity "core" of the exiting viscous flow. 
As the potential differential is increased emission density increases. This 
leads to an increase in the space charge field (or counter field) and to 
an increase in the space charge induced pressure in the bulk fluid. The 
electric field pattern in the vicinity of the emitter tip is thus altered. 
The tip is shielded from the impressed field by the space charge field of 
the emitted charge. The net result is a broadening of the emission region 
with other portions of the emitting tip becoming active. This, coupled 
with the altered electric field, introduces free charge into regions of 
the flow pattern further from the initial high speed "core" region. Added 
to this is the electrostatic pressure produced flow field alteration. The 
overall effect of these processes is to distort the free charge 
trajectories outward from the vicinity of the emitting tip. 
A higher impressed mean electric field will produce increased mobility 
velocity at the same time the outwardly displaced charge encounters flow 
velocities which are reduced from those in the fluid streams "core." A 
point is reached, with increasing voltage, where the electron trajectories 
are sufficiently distorted from their initial configuration to encounter 
the blunt electrode. 
The data indicate that the ratio of mobility velocity (V.sub.m) at the 
breakpoint to mean bulk velocity (V.sub.b) is inversely related to the 
mass flow rate Q. With a coefficient of determination of 0.89 and assuming 
a constant mobility .mu.=1.3.times.10.sup.-7 m.sup.2 /V.Sec; V.sub.m 
/V.sub.b =0.186+0.146/Q. This empirical relation agrees to within 2% with 
that derived using the empirical relation for E.sub.max as a function of Q 
and a fixed ratio of 0.52 between E.sub.b and E.sub.max. Over the range of 
flow rates studied and for the geometry used mobility velocity has to be 
from two to five times lower than the bulk fluid velocity to prevent 
collection of current by the blunt electrode 64. 
With the establishment of current paths to the conducting blunt electrode 
64 the breakpoint is past and current paths continue to broaden with 
further increase in voltage. 
This "model" of Spray Triode operation is reinforced by analysis of spray, 
collected current (I.sub.c) data. Because droplet size is correlated with 
mean specific charge (defined as Ic/Q) the data were plotted as shown in 
FIG. 3 as (Q/M).sup.1/3 vs. -E. Evaluation of those data revealed the 
following: 
1. Maximum observed mean specific charge was equal to 2.48.times.10.sup.-3 
C/kg with a standard deviation of 5.8% independent of flow rate or gap 
spacing. 2. Below the breakpoint I.sub.b O, therefore I.sub.c (i.e. 
Q/M.multidot.Q) and total emitted current are identically related to E; 
viz, the same cubical dependence prevails as observed with total emitted 
current. 3. As a corollary to 2 the same relation between E.sub.b and Emax 
was obtained. The Q/M data yielded a value for this ratio within 1% of the 
0.52 value determined from total current data. 4. Above the breakpoint the 
collected current is less than the total emitted current (i.e. I.sub.b 
.noteq.0). Therefore, the slope of the data line is less than that 
observed for the emitted current, (total emitted current).sup.1/3 vs. E 
data. Whereas the ratio of the slopes, i.e. the ratio of the initial to 
high voltage slope was 1.935 for the emitted current, the corresponding 
ratio for the collected current I.sub.c was 2.234 (standard deviation of 
4%) or some 21% less. Therefore, space charge more severly alters the 
means specific charge than it does the total emitted current. 
The implications of these results are clear. For fixed flow rate mean 
specific charge increases cubically with voltage differential (or 
equivalently with space charge free calculated emitter tip E field) until 
the onset of breakdown. It has been established that limiting tip E field 
is linearly dependent upon flow rate, the higher the mean flow rate (or 
fluid velocity for fixed exit port size) the higher the equivalent E field 
at which breakdown will occur. However, within the range of flow rates 
tested, the limiting condition is characterized by fixed mean specific 
charge. 
TABLE I 
__________________________________________________________________________ 
PHYSICAL CHARACTERISTICS OF EXXON MARCOL 87.sup.+ WHITE OIL 
Property/Temperature 
0.degree. C. 
20.degree. C. 
25.degree. C. 
38.degree. C. 
50.degree. C. 
__________________________________________________________________________ 
Density (kg/m.sup.3) 
0.859 .times. 10.sup.3 
0.847 .times. 10.sup.3 
0.843 .times. 10.sup.3 
0.838 .times. 10.sup.3 
0.833 .times. 10.sup.3 
Viscosity (m.sup.2 /Sec) 
113.19 .times. 10.sup.-6 
37.2 .times. 10.sup.-6 
29.55 .times. 10.sup.-6 
17.58 .times. 10.sup.-6 
11.66 .times. 10.sup.-6 
Surface Tension (N/m) 
0.0333 0.0332 0.0328 0.0323 0.0310 
Molecular Weight (-) 
-- *340 -- -- -- 
Conductivity (Mho/m) 
-- 0.3 .times. 10.sup.-12 
-- -- -- 
__________________________________________________________________________ 
*Average; range 290 to 425. 
.sup.+ Marcol 87 is a mixture of 13% Primol 355 (a naphthalenic oil) and 
87% Marcol 72. 
EXAMPLE II 
Experimental Apparatus 
Tests were conducted using the Spray Triode device displayed in FIG. 6. 
Marcol 87 (Exxon Chemical Co.) was used exclusively as the test fluid. The 
test hand was machined from a Lucite 11/4" OD rod with an 11.9 mm diameter 
cylindrical chamber. The lower portion of this chamber transited into a 
120.degree. converging section which terminated in a 1 mm long 1 mm 
diameter exit port. 
Emitter electrode 38, 11.8 mm diameter OD was fit to the chamber. Typically 
electrode 220 and between 10 mm and 13 mm long. A number of emitter 
electrodes having lengths between 10 mm and 13 mm were tested and behaved 
similarly. Electrode 220 consisted of 85 segments of industrial grade 
razor blades arranged radially with the sharpened edges toward the inside 
and parallel to the unit's center line. The razor blade edges were 
arranged so as to define a cylindrical surface 4.75 mm inside diameter. 
Approximately one meter total length of emitting edge surface was exposed 
on the inside surface. The blade segments were epoxied to form a coherent 
unit with the edges exposed and clear of epoxy. One or more 
circumferential grooves were ground into the outside epoxy surface of the 
blade unit. The groove(s), filled with wound copper wire, electrically 
conducting epoxy or a combination thereof, assured electrical 
communication existed between all blades of the unit. Precise mating of 
220 with the spray chamber was assured by grinding the top and bottom ends 
of smooth, parallel and perpendicular to the chamber centerline. 
Electrical contact with the electrode 38 was made by a bolt contacting the 
razor electrode unit and holding it in place within the chamber 26. The 
bolt passed through the Lucite casing and protruded on the outside where 
contact to the high voltage power supply 40 was made. The emitter exit 
plane was within 1.4 mm of the 1 mm exit port entrance. 
The electrode 64 was coaxially positioned with respect to the emitter 
electrode 38 as shown. Numerous different blunt electrodes 64 were 
successfully used. All electrodes were 3.18 mm diameter (1/8") and 
extended to the exit port entrance. Both brass and stainless steel solid 
rods were used as electrodes in early tests. In addition, a hollow rolled 
stainless steel screen electrode 64 was also successfully used. In fact, 
most data were obtained using this type of electrode structure. Tests of 
various surface materials were conducted with this electrode. In addition 
to the base stainless screen data were obtained with nickel, gold and 
platinum plating. Spray performance correlated positively with increasing 
blunt electrode work function. 
Tests were conducted using resistance (R) values from 100 meg.OMEGA. to 
5000 meg.OMEGA. with the bulk of testing being conducted with R 1000 
meg.OMEGA.. In all instances, Victoreen high voltage resistors 
.+-.1%.+-.5%, tolerance were used. To limit possible damage from flashover 
between the emitting or collecting electrode and the external electrode 
82, a 100 meg.OMEGA. was interposed between electrode 82 and ground. 
Electrometers were used to measure the blunt electrode 64 current I.sub.b, 
the current flow I.sub.e to the external electrode 82 and the spray 
current I.sub.c. A collector receptacle filled with stainless steel wool 
and covered with a stainless steel screen served to collect the spray 
current. This receptacle 15 cm in diameter and 10 cm high, was positioned 
20 cm below the spray head. For those tests involving vigorous spraying a 
15 cm diameter screen extension was mounted on top of the receptacle to 
assure complete spray collection. Receptacle potential was maintained 
close to ground by the electrometer used to measure I.sub.c, for 
measurements in the microampere in the range this resistance corresponded 
to 1 meg.OMEGA.. 
Input current (I.sub.a) to the emitting electrode 38 was monitored using an 
insulated 0-100 .mu.a panel meter. Input voltage V.sub.a was measured at 
this point. Blunt electrode voltage (V.sub.b) was computed from the known 
resistance value R and measured I.sub.b. In all instances the value of R 
was verified over the operating voltage range by shorting electrode (A) 
and (B) under no flow conditions measuring I.sub.b as a function of 
V.sub.a. The V.sub.a /I.sub.b /.sub.A-B shorted =R. 
Measured external electrode collected currents (I.sub.e) were typically in 
the nanoampere range or lower. Therefore except at the highest voltages 
tested (.gtorsim.24 KV) where this electrode produced flow rate 
enhancement (9%) by virtue of the electric field between (E) and the 
charged fluid interior to the device the external electrode was not 
essential. The collection receptacle formed the major return path for the 
charged spray current and therefore functioned as the third electrode of 
the Spray Triode. 
All testing was conducted with a calibrated dropping funnel gravity flow 
system capable of supplying flow rates in the range 1.25 to 1.67 ml/sec. 
Flow rate varied with oil temperature, details of the blunt electrodes 
position with respect to the exit port area and the applied voltage level 
but for each set of conditions was constant to within 3%. Oil temperatures 
were in the range 18.degree. C. to 24.degree. C. 
In all tests, within experimental accuracy it was verified that total 
emitted current I.sub.a equalled the sum of the blunt electrode current 
I.sub.b and the collected current I.sub.c i.e. I.sub.a =I.sub.b +I.sub.c. 
No quantitative measurements of droplet number or charge to mass ratio 
distribution were obtained. The presence of spraying and a qualitative 
indication of its vigor were noted for each test. Therefore V.sub.a, 
I.sub.b, I.sub.c, the flow rate m and the value of resistance R used were 
the major quantitative parameters recorded for each test. 
In the first test with the Spray Triode stable spraying was obtained for 
-22 -V.sub.a 27.5 KV with R=1800 meg.OMEGA.. Vigorous break-up of the jet 
occurred .about.5 cm downstream of the head. By contrast when the resistor 
between the blunt electrode and ground was disconnected (R-.infin.) no 
spraying occurred for V.sub.a up to -271/2 KV. In these tests the external 
electrode was in place. With only two electrodes (electrode 64 
disconnected) the device functioned as a spray diode. In this mode the 
exiting stream remained a laminar glassy smooth circular jet 1 mm diameter 
from the spray head to the receptacle. No physical alternation could be 
observed as applied voltage V.sub.a was increased up to the maximum used, 
30 KV. Collected currents I.sub.c were in the nanoampere range for 
operation as a diode. 
The Spray Triode produces spraying by forceably injecting charge into the 
liquid to be atomized. Electrons are field emitted from the sharp edges of 
razor electrode 38 under the action of the electric field that exists 
between 38 and 64. Therefore the fluid in the annular gap 224 has an 
excess free charge. The physical displacement of charged fluid from the 
annular gap region to the exterior permits liquid fragmentation to 
proceed. 
An approximate model of this process, against which the experimental data 
can be compared, and the overall validity of the concept tested, can be 
developed. A tractable model can be constructed if it is first assumed 
that space charge effects (i.e. the free excess change that is forceably 
injected into the liquid can be neglected). Further neglecting edge 
effects, the electric field in the gap interior 
##EQU1## 
where .sqroot.a=interior radius of emitting electrode 212; .mu..sub.b 
=radius of blunt collecting electrode 64; V.sub.ab =gap potential 
difference=V.sub.a -I.sub.b R. 
Ideally, the emitting electrode should be interior to the blunt electrode. 
With this arrangement the field emitter edges would be in the strongest E 
field possible for a given applied gap voltage. Fabrication difficulties 
forced the emitters to be constructed as noted. 
Considering conditions in the vicinity of the blunt electrode 64 we can 
write, using the electrode dimensions 
EQU E.sub.b =1.89.times.10.sup.3 V.sub.ab (V/m) 
using .sqroot.a=2.38 mm, .sqroot.b=1.58 mm 
Current density at the blunt electrode surface is J.sub.b =V.sub.m .rho.e 
(A/m.sup.2) where 
V.sub.m =mobility velocity of the charge carriers (m/sec) 
.rho.e=free excess charge density in the fluid (C/m.sup.3) 
The mobility velocity in the vicinity of the blunt electrode surface is, by 
definition, 
EQU V.sub.mb =.mu.E.sub.b 
where .mu.=mobility of electrons in the liquid m.sup.2 /V.sec. 
Since I.sub.b =J.sub.b A.sub.b where A.sub.b =lateral area of the blunt 
electrode (for 13 mm long blunt electrode A.sub.b =1.04 cm.sup.2.) 
we write 
##EQU2## 
Numerically using the dimensions noted 
##EQU3## 
Extensive data taken at voltages 20 KV.ltoreq.-V.sub.a .ltoreq.28 KV, 
I.sub.b up to .about.30 .mu.a and 500 meg.OMEGA..ltoreq.R.ltoreq.5000 
meg.OMEGA.permitted the following empirical relationship to be developed 
for a spray head using stainless steel screen blunt electrode and 
operating on Marcol 87. 
EQU V.sub.a /I.sub.b =0.401.times.10.sup.9 +1.30 R 20 KV.ltoreq.-V.sub.a 
.ltoreq.28 KV 
All data fell within .+-.10% of this line. An empirical least mean square 
fit to the data taken in the range 15 KV.ltoreq.-V.sub.a .ltoreq.28 KV 
with the same resistance values resulted in a similar expression. 
EQU V.sub.a /I.sub.b =0.58.times.10.sup.9 +1.28 R 15 KV.ltoreq.-V.sub.a 
.ltoreq.28 KV 
with all data falling within .about.20% of this line. 
The non-unity coefficient of R is interpreted as a manifestation of space 
charge effects, which were neglected in the simplified model expression. 
Making a direct comparison between the empirical expression (-V.sub.a, 20 
KV to 28 KV) and the idealized expression permits the .mu..rho..sub.e 
product to be estimated as 
EQU .mu..rho..sub.e =1.3.times.10.sup.-8 (mho/m) 
Note that .mu..rho..sub.e can be considered an effective conductivity. 
Compare this value with the intrinsic conductivity of Marcol, cf. Table 1. 
For hydrocarbons in general 10.sup.-8 .ltoreq..mu..ltoreq.10.sup.-7 or 
.rho.e.gtoreq.0.13 C/m.sup.3. The free excess charge density .rho..sub.e 
is simply related to the fluids charge to mass ratio Q/m C/kg. 
Q/m=.rho..sub.e /.rho. 
where .rho.=mass density kg/m.sup.3. For Marcol 87, .rho.=845 kg/m.sup.3. 
It is therefore anticipated that Marcol sprays from the spray triode 
described should have a charge to mass ratio of 
Q/M.gtorsim.1.5.times.10.sup.-4 C/kg. 
Up to this work no data were available concerning the mobility of Marcol 
87. Measurements of I.sub.c and mass flow permitted the mean charge to 
mass ratio to be obtained Q/M/.sub.mean =I.sub.c /m. Mean charge to mass 
ratios of from 1.times.10.sup.-4 to 2.2.times.10.sup.-4 C/kg have been 
consistently observed using the device depicted in FIG. 6. These data 
permit the mobility of Marcol to be obtained directly from the measurement 
of I.sub.b, I.sub.c and V.sub.a 
##EQU4## 
where Q=volumetric mass flow in ml/Sec. 
Numerically for the geometry noted 
##EQU5## 
Plotting I.sub.b /I.sub.c vs (V.sub.a -I.sub.b R) a linear regression fit 
to the data permitted the following relation to be developed-- 
EQU I.sub.b /I.sub.c =61.24+14.37.times.10.sup.-3 [-(V.sub.a -I.sub.b R)] 
The constant factor represents an offset voltage (-4.26 KV) below which no 
emission was observed. Above this value the data taken at Q=1.67 ml/sec 
flow rate admitted to a mean mobility of 
EQU .mu.=1.29.times.10.sup.-7 m.sup.2 /V.sec. 
This corresponds to a mean charge to mass ratio of 1.2.times.10.sup.-4 
C/kg. A maximum gap potential difference of 11 KV was observed. Beyond 
this value, breakdown would occur. This corresponds to a maximum 
sustainable electric field of E.sub.b =2.08.times.10.sup.7 V/m. 
It is worth noting that the measured conductivity of fresh Marcol is 
3.times.10.sup.-13 mho/m. After several months of use the remeasured 
conductivity was found to be 9.times.10.sup.-13 mho/m or less. Using this 
value and the maximum E field the maximum conduction current density is 
EQU J=gE=1.87.times.10.sup.-5 A/m.sup.2 
For a total blunt electrode area of 1.04 Cm.sup.2 this corresponds to 
I.sub.b .about.2.eta.a. By comparison, I.sub.b for V.sub.ab .apprxeq.-11 
KV.about.30 .mu.a. Therefore, in this case charge injection by field 
emitting electron with the spray fluid has lead to a current enhancement 
by a factor of at least 10.sup.4. 
Mobility velocity under maximum E field conditions .about.2.68 m/sec. By 
contrast mean fluid velocity was typically 0.17 m/sec. From this and the 
known flow passage geometry the ratio I.sub.c /I.sub.b can be roughly 
estimated. The calculated value I.sub.c /I.sub.b 0.005 is about half the 
observed value. This divergence between theory and observation is not 
unexpected in light of the neglect of both space charge and fringe field 
effects, and the details of the viscosity dominated flow field. 
Emitted current density for maximum sustainable electric field conditions 
(V.sub.ab .apprxeq.-11 KV), is from the empirical relation for (-V.sub.a, 
15 to 28 KV and R=1000 meg.OMEGA.).about.5.5 .mu.a/cm.sup.2. 
EXAMPLE III 
Initial exploratory experiments were conducted using the device shown in 
FIG. 7. Marcol 87 flowed under gravity from a 500 ml dropping funnel 
positioned .about.1 m above the spray head at a mean flow rate of 1.2 
ml/sec. Dropping funnel fluid height was maintained at a constant level by 
a small pump which returned the spray fluid to the funnel. Electrode 38 
was formed from a Dyno Item 228 nickel plated straight pin 223 whose tip 
was burnished sharp on glass under oil. Blunt electrode 64 consisted of a 
4-40 stainless steel machine screw positioned coaxially with respect to 
pin electrode 38. The polished end of 64 was 2 mm from 221. The gap was 
symmetrically disposed with respect to the center line of the luctie head. 
The interior chamber consisted of a 6.35 mm .phi. (1/4".phi.) diameter 
cylindrical section coaxial with the spray head. A 120.degree. conical 
transition connected the chamber with the 1 mm .phi., 1 mm long 
cylindrical exit port. 
The common electrode centerline was perpendicular to the chamber and 1 cm 
upstream of the exit port plane. A 0.64 mm thick stainless steel disc 31 
mm OD with a 6 mm diameter hole, positioned flush with the exit port 
formed the external electrode 82. 
Electrode 38 was energized by a high voltage power supply (NJE), capable of 
supplying up to 35 KV. A variety of high voltage resistors 72 were used to 
connect electrode 64 to ground. Most tests were conducted using three 100 
meg..OMEGA. resistors in series (R.about.331/3 meg..OMEGA.). The external 
electrode 82 was connected to ground via a 15 meg..OMEGA. resistor which 
acted to limit current surge when breakdown occurred. 
In this configuration charge injection was localized to the electrode gap 
region. Approximately 20% of the fluid flow passed thru the gap region, 
the remainder flowing outside the gap charge injection region. Injected 
charge was measured by collecting the exit stream in an isolated metal 
receptacle 15 cm in diameter. The top of which was located .about.15 cm 
below the exit plane. Collected current (I.sub.c) was measured with an 
electrometer. 
A limited series of tests were conducted with the apparatus. Visual 
inspection of the exit jet was used as the primary measure of charge 
injection. Low values of I.sub.c (.ltorsim.10 na) made quantitative 
evaluation of this parameter too uncertain to be reliable. 
With R.apprxeq.331/2 Meg.OMEGA. the exit jet remained glassy smooth 
(laminar) to applied voltages (Va) up to .about.-20 KV. Above this level a 
region of turbulence and breakup could be observed at the bottom of the 
jet where it entered the steel wool in the receptacle. As voltage was 
increased beyond this level, the breakup region monotonically rose toward 
the head until at the maximum voltage tested (-27.5 KV), it was observed 
to start .about.3 cm below the head. 
At the maximum voltage condition, the lower portion of the breakup region 
had spread to a diameter of .about.4 mm and was observed to be composed of 
droplets on the order of 1 mm in diameter. Tests under similar conditions 
with the external resistor disconnected, i.e. operating the device as a 
spray diode produced fundamentally different results. The exit jet 
remained a glassy smooth rod from exit plane to receptacle entrance, 
independent of voltage, up to and including the maximum used (-27.5 KV). 
This difference in behavior was taken as clear evidence of charge injection 
induced breakup, but was too qualitative for proof of concept validation.