Fluid sprinkling – spraying – and diffusing – Electrostatic type
Reexamination Certificate
1999-10-29
2001-03-27
Morris, Lesley D. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Electrostatic type
Reexamination Certificate
active
06206307
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrostatic atomizers and to devices in which atomization of liquid is used, including fuel atomizers and combustion devices.
BACKGROUND OF THE INVENTION
Electrostatic atomizers disperse liquid by applying a net electrical charge to the liquid, typically as a stream of the liquid passes through an orifice. The negative charges developed within the liquid tend to repel one another, dispersing the liquid into droplets. The injection of the net charge into the liquid may be accomplished utilizing a pair of opposed electrodes arranged adjacent to the stream of liquid and electrically connected to a high voltage power source. Such an electrostatic atomizer, called the SPRAY TRIODE™ atomizer, is disclosed in certain embodiments of U.S. Pat. No. 4,255,777, the disclosure of which is hereby incorporated by reference herein. Another electrostatic atomizer utilizes an electron beam to apply a net negative charge to the liquid. Certain embodiments of U.S. Pat. Nos. 5,093,602 and 5,378,957, the disclosures of which are hereby incorporated by reference herein, disclose apparatus and methods for electrostatic atomization utilizing an electron beam.
Electrostatic atomization of Newtonian fluids adheres to the following equation: D=75/&rgr;
e
. D is the mean droplet size in microns and &rgr;
e
is the charge density of the fluid, in coulombs per meter cubed. Thus, the same size droplets will be produced whenever a particular charge density is achieved.
The greater the charge density injected into the liquid, the greater the droplet dispersion, the smaller the droplet size and the narrower the droplet distribution. A limit on the charge density which can be injected into the liquid is the phenomenon of corona-induced breakdown, which interrupts dispersion of the liquid. When a critical level of charge is reached, the spray plume collapses.
FIG. 7A
shows a spray plume during uninterrupted operation and
FIG. 7B
shows a spray plume during operation interrupted by corona-induced breakdown. For a combustion device, this means interruption of the flame operating on the electrostatically atomized fuel.
For example, a combustion device has been run on fuel atomized by the SPRAY TRIODE™ electrostatic atomizer. It was found that sustained operation close, i.e., within 50V, to the critical level for corona-induced breakdown, which was about 5 kV or more, was required for blue flame operation. However, when the net charge reached the critical level, operation of the combustion device was dramatically interrupted. Furthermore, the critical level of net charge at which corona-induced breakdown occurs depends upon the properties and flow rate of the fuel, which vary during operation of the combustion system. Changes in ambient pressure and temperature also affect the operation of the electrostatic atomizer.
It would be desirable to develop an electrostatic atomizer with improvements in sustained operation and the maximum charge density provided to a liquid.
SUMMARY OF THE INVENTION
The present invention addresses these needs.
An aspect of the present invention provides an electrostatic atomizer comprising a charge injection device for injecting a net charge into a fluent material to thereby atomize the fluent material, a power source for powering the charge injection device, a controller for controlling the net charge injected by the charge injection device, and a sensor for sensing breakdown precursors in the vicinity of the orifice. The sensor produces a feedback signal upon the occurrence of the breakdown precursors, the sensor being in communication with the controller. The controller is responsive to the feedback signal so that upon occurrence of the feedback signal, the controller decreases the net charge injected.
The controller varies the net charge injected into the stream of liquid to avoid corona-induced breakdown, which interrupts the atomization of the liquid. Corona-induced breakdown occurs at a particular level of net charge for the charge injection device. By controlling the level of net charge in response to the feedback signal, corona-induced breakdown is avoided, but the system operates on the highest level of net charge which can be used without corona-induced breakdown. During the onset of corona-induced breakdown, breakdown precursors develop in the vicinity of the orifice of the electrostatic atomizer. Accordingly, when breakdown precursors are sensed, the controller reduces the level of net charge injected into the stream of liquid by a predetermined amount.
In certain preferred embodiments, the controller is arranged to progressively increase the net charge until the feedback signal occurs, decrease the net charge injected by a predetermined amount in response to the feedback signal, and then progressively increase the net charge until the feedback signal recurs. The net charge may be decreased by a predetermined amount and then progressively increased after a predetermined dwell time has lapsed. Depending on the amount of decrease applied in response to the feedback signal, the rate of progressive increase, and conditions prevailing in the fluid flow, the controller may cause the amount of charge injected to rise and fall repeatedly so that during some brief intervals, the level of charge is above the level which can be applied without corona breakdown. As further explained below, charge levels above the long-term breakdown level can be applied for short intervals. In certain preferred embodiments, the system repeatedly brings the charge level up above the long-term breakdown level, which yields breakdown precursors and triggers the feedback signal, then decreases the charge level to or below the long-term breakdown level, responsive to the feedback signal, and then raises the charge level again. The overall result is a time-average charge level above the long-term breakdown level without breakdown.
In certain preferred embodiments, the controller is arranged to vary the net charge injected so that the net charge varies in accordance with a predetermined pattern of variation until the feedback signal occurs.
In certain preferred embodiments, the charge injection device includes a first surface and a second surface spaced apart from one another and disposed within the body. The power source provides a potential difference between the first and second surfaces so that a net charge may be injected into the stream of liquid. The first electrode may comprise a conically-shaped electrode having a pointed end, or any other shape. The second electrode comprises a surface having at least one aperture formed therein. The charge injection device, in other embodiments, includes an electron gun. Any charge injection device for injecting a fluent material with a net charge may be used.
In preferred embodiments, the electrostatic atomizer further comprises a body defining an orifice, the fluent material being a stream of liquid passing out of the orifice.
The sensor, in certain preferred embodiments, includes a loop antenna encircling the orifice. In other embodiments, the body is electrically connected to the sensor for sensing the breakdown precursors. In this embodiment, the atomizer includes a housing and the body is electrically isolated from the housing.
The net charge injected into the fluent material is related to the operating voltage applied to the charge injection device. In preferred embodiments, the controller is arranged to control an operating voltage applied to the charge injection device and to vary the operating voltage so that the operating voltage progressively increases until the feedback occurs, decreases in response to the feedback signal, and then progressively increases. The operating voltage is decreased by the controller by a predetermined amount and then progressively increased after a predetermined dwell time has elapsed.
In other preferred embodiments, the controller is arranged to control the operating voltage and to vary the operating voltage in accordance with a predetermined pattern of variation
Kelly Arnold J.
Prahl Frederick
Charged Injection Corporation, by said Arnold J. Kelly
Lerner David Littenberg Krumholz & Mentlik LLP
Morris Lesley D.
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