US3784876A

US3784876A - Static decharger

Info

Publication number: US3784876A
Application number: US00244698A
Authority: US
Inventors: De Gaston A Neal
Original assignee: McDonnell Douglas Corp
Current assignee: McDonnell Douglas Corp
Priority date: 1972-04-17
Filing date: 1972-04-17
Publication date: 1974-01-08
Anticipated expiration: 1991-01-08

Abstract

Electrostatically charged nonconducting fluid is rendered temporarily conductive by subjecting the fluid to ionizing radiation of selected radioactive material. Ion pairs are created by the radiation and a predetermined density of ions is produced whereby the fluid is made sufficiently conductive so that it practically cannot hold a charge. While conductive, any acquired charge is free to drain to ground. A volume ionizing embodiment of the invention includes radioactive material disposed in a grounded grating configuration through which the fluid flows and is ionized, and any fluid charge is largely drained to ground through the grating. In another version of the invention, a laminar ionizing embodiment includes radioactive material disposed in a sleeve configuration through which the fluid flows and an adjacent layer of fluid having an opposite charge to its fluid core is produced, and charge neutralization is achieved by subsequent mixing of the fluid layer and core.

Description

United States Patent [1 1 De Gaston STATIC DECHARGER [75] Inventor: Alexis Neal De Gaston, Orange,

Calif.

[73] Assignee: McDonnell Douglas Corporation,

' Santa Monica, Calif.

22 Filed: Apr. 17, 1972 21 Appl. No.: 244,698

[52] US. Cl. 317/2 R, 317/2 J OTHER PUBLlCATlONS Electrostatics in the Petroleum Industry edited by A. Klinkenberg, Elsevier Publishing C0., 1958, pp. 73-74.

A.P.C. Application of Peycelon et al., Ser. No. 376,930, Published May 25, 1943.

F062 PESERVO/R fil/v/r (UNDEQGROU/VD) Jan. 8, 1974 Primary Examiner-J. D. Miller 7 Assistant ExaminerHarry E. Moose, Jr. Attorney-Walter J. Jason et al.

[57] ABSTRACT Electrostatically charged nonconducting fluid is rendered temporarily conductive by subjecting the fluid to ionizing radiation of selected radioactive material. ion pairs are created by the radiation and a predetermined density of ions is produced whereby the fluid is made sufficiently conductive so that it practically cannot hold a charge. While conductive, any acquired charge is free to drain to ground. A volume ionizing embodiment of the invention includes radioactive material disposed in a grounded grating configuration through which the fluid flows and is ionized, and any fluid charge is largely drained to ground through the grating. In another version of the invention, a laminar ionizing embodiment includes radioactive material disposed in a sleeve configuration through which the fluid flows and an adjacent layer of fluid having an opposite charge to its fluid core is produced, and charge neutralization is achieved by subsequent mixing of the fluid layer and core.

18 Claims, 11 Drawing Figures PATENTEU JAN 8 i874 sum 3 BF 6 PATENIED JAN 8 IBM saw so; a

BAA/65f? LEVEL 1 PRES/DUAL Q/ARGE AWE/f (SH/W615 AAA 5m @6004 04 155 M1 '93 FLOW AM 75 KGPM) STATIC DECHARGER BACKGROUND OF THE INVENTION My invention pertains generally to the field of electrostatic charge reduction in variously charged substances. More particularly, the invention relates to a novel means and process of neutralizing electrostatic charges in an electrically charged fluid (gas, liquid or vapor) by the use of nuclear radiation.

The problems caused by static electricity in and on various substances are well known. The problem of reducing electrostatic charges in flammable liquids quickly and surely to a safe level is, of course, a particularly serious one. A discussion of the nature of the problem, and of different methods and devices for removal of electrostatic'charg'es from flammable liquids is, for example, presented in U.S.Pat. No. 3,383,560 of Irwin Ginsburgh for Method and Apparatus for Neutralizing Electrostatic Charges in an Electrically Charged Liquid, patented May 14, I968. The method and apparatus shown, described and claimed by Irwin Ginsburgh avoid certain of the shortcomings of the earlier methods and devices, and are presently in widespread use throughout the petroleum and distillate (gasoline, jet fuel, etc.) industries.

The apparatus claimed by Irwin Ginsburgh functions under a method which works on the charge injection principle. Briefly stated, a high voltage is developed by flowing a charged liquid through a tubular capacitor comprising an inner nonconductive dielectric of high resistivity and low dielectric constant and a grounded conductive outer plate, and as the charged liquid flows through the capacitor it contacts a plurality of spaced, sharply pointed, grounded electrodes which inject charges of opposite sign into the liquid to neutralize its charge. Among the difficulties encountered with such apparatus was that while at times it would remove 95 percent or better of the charge, this maximum effectiveness was reached only after about 1/2 to l /2 minutes, under varying circumstances, of liquid flow. Furthermore, often as little as to 50 percent of the charge was removed from the liquid. It was found that even slight contamination of the inner dielectric surface due to some impurities deposited thereon by the liquid greatly degrades the performance of the apparatus. In addition, attempts at scaling this apparatus down to a smaller physical size reduced its optimum performance capability of charge removallto a maximum of about 75 to 80 percent, and this was reached in certain specific tests only after approximately 5 minutes.

The use of nuclear radiation for neutralizing electrostatic charges on a moving substance has been known for a very long time. Such use, however, has been with fibrous materials and tape, for example, as exemplified by U.S. Pat. No. l,l54,l27 of Paul Rasehorn and Gustav Grossman for Apparatus for Neutralizing Electric Charges in Fibrous Materials, patented Sept. 21, l9l5 and U.S. Pat. No. 2,264,683 of Donald W. Smith for Method of and Means for Neutralizing Electrostatic Charges on Moving Tapes and the like, patented Dec. 2, 1941. In these instances, the radiation serves to ionize the adjacent air which then functions to remove or neutralize the charges on the moving substance. In spite of the long period of time that nuclear radiation has been used for neutralizing electrostatic charges on different substances, the adjacent air has always been ionized for the purpose of removing the charge.

Throughout this long period, there has been no known or successful direct application of nuclear radiation to ionize a charged substance itself (particularly a liquid) and thereby neutralize the same.

SUMMARY OF THE INVENTION Briefly, and in general terms, my invention is prefera' bly accomplished by subjecting an electrostatically charged but inherently noncon'ducting fluid (which can be a gas, liquid or vapor or a fluid carrying solid particles, etc.) to ionizing radiation of a selected radioactive material to creat ionpairs so that a predetermined density of ions is produced whereby the fluid is temporarily rendered sufficiently conductive and practically cannot hold a charge and, while conductive, any acquired charge in the fluid is allowed to drain to ground. Means for performing the above process is provided to decharge a fluid. As used herein, decharge" means the removal of charge from a fluid and discharge means the expelling of the fluid itself, as from a pipe or into a tank.

A fluid volume ionizing embodiment of the invention includes radioactive material disposed in a grating configuration through which the electrostatically charged fluid flows and is ionized. The radioactive material can be suitably encased in metallic strips, and these radioactive strip elements are mounted in discretely spaced relationship within a frame to provide a grating configuration. This grating isinstalled in a suitably shielded housing through which the fluid flows. The housing is grounded, and the plane of the grating is positioned therein at approximately right angles to the general direction of fluid flow therethrough. The configuration of the radioactive elements and their spacing within their mounting frame are selected to produce a sufficient density of ions throughout the entire volume of the fluid flowing at any rate in a given range of flow rates through the grating. The fluid is thus rendered sufficiently conductive so that any acquired charge therein can be rapidly relaxed or drained to ground.

Ground is provided by the housing and also normally by the grating which is preferably installed with good electrical contact to the groundedhousing. A good contact is, for example, obtained through a box spring assembly positioned between the grating and the housing. The box assembly illustratively includes a lower base frame and an upper ground grid which is supported on the base frame and is spring biased therefrom; The base frame preferably mounts a few, short, sharp blades which can cut into the upper surface of the grating to obtain a good electrical contact therewith, and the upper grid is positively attached to the upper half of the grounded housing. The box assembly is located downstream of the grating and provides added mechanical strength thereto. The ground grid structure assists in the control of fluid flow and provides more conductive surface for removal and neutralization of any remaining ions and charges in the fluid if still present at that point. It is noted that the ground grid is not essential or even really necessary under normal conditions, and can be omitted from the volume ionizing embodiment of the invention if desired.

Similarly, the volume ionizing embodiment can optionally include a charge extractor located upstream of the radioactive grating to reduce any exceptionally high charge level (in excess of 300 microcoulombs/cubic meter, for example) in the fluid to a lower one before reaching the grating. The extractor can include a series of needle bars secured in parallel and spaced relationship within a frame corresponding in size and shape generally to the grating frame. The extractor is installed in good contact to the grounded and shielded housing with the plane of the extractor frame positioned therein at approximately right angles to the general direction of fluid flow therethrough. Each needle bar mounts a few spaced, sharply pointed, electrodes which are oriented perpendicularly to the plane of the extractor frame. The extractor is preferably installed in the housing so that its electrodes (needles) point upstream.

Another version of the invention includes a laminar ionizing embodiment wherein radioactive material is disposed in a sleeve configuration through 'which the fluid flows. A cylindrical metallic sleeve encases selected radioactive material therein, for example, and the sleeve is positioned within a longer section of pipe contiguously to its inner surface. The pipe section is suitably shielded and can be installed as a connecting length of (grounded) piping through which fluid is flowed. This configuration of the invention functions differently from the grating configuration in that positively charged fluid flowing in the pipe induces a negative charge on such pipe, then when the fluid flows over the radioactive sleeve, the induced charge effectively moves onto a laminar layer of fluid adjacent and concentric to the sleeve, and charge neutralization is subsequently achieved downstream by mixing of the fluid layer and its core which have equal and opposite,

charges.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be more fully understood, and other features and advantages thereof will become apparent, from the following description of two exemplary embodiments of the invention. The description is to be taken in conjunction with the accompanying drawings, in which:

FIG. II is a schematic block diagram ofa test rig setup utilized to test a full scale decharger constructed according to this invention;

FIGS. 2A, 2B, 2C and 2D, together, comprise an exploded view of an illustrative, volume ionizing, embodiment of the invention;

FIG. 3 is a fragmentary front elevational view of a box spring assembly used in the illustrative, volume ionizing, embodiment;

FIG. 4 is a side elevational view, shown partly in section, of the box spring assembly as taken along the line 44 indicated in FIG. 3;

FIG. 5 is a graph showing plots of charge density versus fluid flow rate and which depict typical performance of the illustrative, volume ionizing, embodiment of the invention;

FIG. 6 is a central sectional view of an illustrative, laminar ionizing, embodiment of this invention; and

FIGS. 7A and 7B are diagrams illustrating flow velocity profiles of fluids respectively having zero and some viscosity flowing through a sleeve.

DESCRIPTION OF THE PRESENT EMBODIMENTS In the following description of two exemplary embodiments of my invention and its associated processes, some specific dimensions and types of materials are disclosed. It is to be understood, of course, that such dimensions and types of materials are given as examples only and are not intended to limit the scope of the invention in any manner.

FIG. 1. is a schematic block diagram of a test rig setup l0 utilized to test a full scale decharger l2 constructed according to this invention. The decharger 12 was constructed to decharge Jet-A fuel flowing at a nominal rate of 600 gallons per minute (gpm) and a maximum charge of 300 micro-coulombs/second (u-c/s). In the setup l0, underground tank 14 has a capacity of about 8,000 gallons of fuel which can be pumped out by pump 16 and circulated through a regular maintenance and cleaning filter 18, fuel flow rate meter 20, then through either valve 22 to bypass line 24 or valve 26 to a charge generating filter 28, through first charge density meter 30, then through either valve 32 to bypass line 34 or valve 36 to decharger l2, and through second charge density meter 38 back into the underground tank. Flow rates up to approximately 1,250 s xiatssttsiaabls,is, the 4 1 1 the Piping is made of 4-inch inside diameter pipe, and 4,000gallons of Jet-A fuel are used in the recirculating system, for example. The filter 28 is used to simulate actual refueling conditions by charging the fuel to 200 to 300 microcoulombs/cubic meter (u-c/m).

The exemplary decharger 12 basically includes a nuclear irradiator 40 installed in a shielded container 42 wherein the fuel is constrained to flow from the lower half through the irradiator to the upper half of the container. The container 42 is, for example, a steel container formed from bolting lower and upper

truncated pyramids

44 and 46 together at their abutting base flanges 48. The steel is overlaid by'a suitable thickness of lead to provide adequate shielding, and the

pyramids

44 and 46 have 4-inch inlet and

outlet pipes

50 and 52, respectively, extending through a wall of each pyramid. A wide mesh wire screen (not shown) is installed in each of the

pipes

50 and 52 as a precautionary measure to catch any radioactive strip element or other component part of the irradiator 40 in the remote event that any of such items are dislodged or broken loose. The container 42 is, of course, grounded as schematically indicated in FIG. 1.

There is an electrostatic ignition hazard associated with the handling of jet grade fuels. This hazard is directly related to two attributes of the fuels, which are their low conductivities and their vapor pressures. The former enables the fuels to become charged with sufficient electrostatic energy so as to ignite appropriate fuel vapor-air mixtures. Vapor pressures of fuels in this class at ordinary handling temperatures provide the right fuel-to-air ratio to create a hazardous explosive mixture. Charge build-up can be prevented or significantly reduced by using impure fuel, not filtering the fuel, and/or moving the fuel slowly. The use of impure fuel is objectionable. in jet engines, and even pure fuel must be purified again before using, thusrequiring the use of filters. The economics of fueling large aircraft is, of course, incommensurate with the use of low fuel rates. Filtering produces 10' to 200 times more charge than generally occurs without filtering, and a normal flow ratewould not allow enough time for the charge to leak off before being concentrated in-a receiving tank.

FIGS. 2A, 2B, 2C and 2D, placed adjacently together in an ascending sequential order, comprise an exploded view of the decharger 12. FIG. 2A is a perspective view of the lower pyramid 44 which is generally symmetrical to the upper pyramid 46 except that the lower pyramid is additionally provided with a drain line 54 connecting with its interior and having a pet cock 56 at the end of the line. Of course, the inlet pipe 50 is located in a wall 58 opposite to that in which the outlet pipe 52 of the upper pyramid 46 is located. Both lower and

upper pyramids

44 and 46 are provided with a lead ring seal 60 which is positioned along the offset base flange 48 as illustrated. Also, a recessed retaining shoulder ledge 62 is provided a short distance within opening 64 below the base surface 66 around the interior walls of both of the

pyramids

44 and 46. A number of bolts 68 can be suitably used to secure the

pyramids

44 and 46 together completely around the flanges 48.

FIG. 2B is a perspective view of a lead gasket 70 and a charge extractor 72 used in the decharger 12. The gasket 70 is normally positioned between the base surfaces 66 and ring seals 60 of the lower and

upper pyramids

44 and 46 when secured together by the bolts 68. The gasket 70 has a rectangular opening 74 which corresponds in size to the base surface openings 64. The extractor 72 includes a series of needle bars 76 affixed in a parallel and spaced arrangement within a frame 78 which fits in and against the retaining shoulder ledge 62 (FIG. 2A) in the lower pyramid 44 in good ground contact therewith. Each of the bars 76 mounts, for example, three equally spaced and sharply pointed electrodes 80 which extend perpendicularly from the plane of the frame 78. These electrodes 80 extend approximately 0.5 inch from their mounting bar 76 and can be made from commercially available, stainless steel, sewing needles cut to the necessary length and suitably welded to a mounting bar. lllustratively, there can be seven equally spaced needle bars 76 made of aluminum and affixed in an aluminum frame 78 which is approximately 17 inches long and 8 inches wide. As stated previously, the charge extractor 72 is optional and can be omitted from the decharger 12 if desired.

FIG. 2C is a perspective view of the nuclear irradiator 40 and a box spring assembly 82 used in the exemplary decharger 12. The nuclear irradiator 40 is, in this instance, provided in the form of a radioactive grating 84 including a substantial number of radioactive strip elements 86 mounted therein. The elements 86 can be, for example, strips formed from strontium silicate (SrSiO beads or microspheres encapsulated in aluminum (Al) and then covered with a thin layer of stainless steel. The ends of each of the strip elements 86 are installed in a correspondingpair of a number of slots 88 provided in mounting frame 90. The slots 88 are each approximately 0.1 inch deep, 0.4 inch long and are open at the lower surface of frame 90. After the elements 86 are installed in the slots 88, a thin retainer plate 92 is fastened to the lower surface of the frame 90 by screws 94 to secure the elements firmly in place. Each strip element 86 is, for example, 3.75 inches long, 0.4 inch wide and 0.1 inch thick, and the elements are mounted in parallel with a center-to-center spacing between successive elements'of 0.4 inch. The peripheral dimensions of the grating 84 and its retainer plate 92 are substantially equal to those of the extractor frame 78, and the lower peripheral surface of the retainer plate is normally held in contact with the upper peripheral surface of the extractor frame by action of the box spring assembly 82. i

The radioactive strip elements 86 are high integrity beta radiation sources which can withstand severe operating conditions. The 74 strontiumelements 86 produced approximately 9,175 curies; however, because of their relatively heavy encapsulation, only about 15 percent energywise or effectively 1,373 curies of the beta activity was available. From this level of radiation, for a nominal fuel flow rate of 600 gpm, at 300 u-c/m and a judiciously estimated ion mobility rate of 0.75 X 10 m /sec-volt, a relaxation time of approximately 6 milliseconds is obtained in the radioactive grating 84 configuration. The available relaxation time due to (nominal) fuel velocity is about 0.016 sec. Since the range of testing was from about to 1,200 gpm and because of the uncertainty in the value of ion mobility rate and the number of effective ion pairs produced, the difference between the relaxation time and time available is not excessive.

Box spring assembly 82 includes a lower base frame 96 and an upper ground grid 98 which is supported on, for example, six biasing springs 100. The springs 100 are helical compression springs installed about respective pendent (from the upper grid 98) pins 102 that extend through guide holes 104 and into displacement channels 106 in the ends of the base frame 96. Retainer nuts 108 are tightened to the lower ends of the pins 102 and fit within the channels 106. Four small and sharp blades 110 (razor blade segments) are secured to the lower surface of base frame 96 in respective slots 112 with a suitable electrical bonding substance. The blades 110 extend approximately 0.06 inch below the lower surface of the base frame 96 and normally cut into corresponding points of the upper surface of the grating frame 90 to obtain good electrical connections therewith. The upper grid 98 is of aluminum and supports, for example, nine aluminum plates or bars 114 which are spaced approximately 2 inches (center-to-center) apart between successive bars. The bars 114 can be approximately 7.68 inches long, 0.75 inch wide and 0.125 inch thick, and can be welded at the ends to the sides of the ground 98. The grid 98 is generally unnecessary for ion ground usage and its primary function is being part of the box spring assembly82 which serves mainly as a spring biasing and cushioning device.

F 10. 2D is a perspective view, shown partially broken away sectionally, of the upper pyramid 46. As mentioned previously, the pyramid 46 is similar to the lower pyramid 44 (FIG. 2A) except for minor inconsequential differences. It includes a steel container 42 half with, for example, about 4 inches of lead shielding l 16, outlet pipe 52 (corresponding to the inlet pipe 50 of the lower pyramid 44) and a lead ring seal 60 (not shown). A number of bolts 68 is used with the nuts 118 and washers 120 shown in FIG. 2A to secure the lower and

upper pyramids

44 and 46 together. In certain areas just opposite to the inlet and outlet pipes, the bolts 68 can be used to engage tapped structural holes where space is unavailable to accommodate the nuts 118 and washers 120. The relatively thick lead shielding 116 is provided largely because of bremsstrahlung (high en ergy gamma radiation) formation resulting from high velocity beta particles passing close to (and deflected by) nuclei.

The nuclear irradiator 40 having the grating 84 com figuration (FIG. 2C) provides high fuel volume ionization using beta radiation sources (radioactive strip elements 86) with a comparatively small bremsstrahlung formation. Radiations other than beta can, of course, be used to cause ionization of a fluid to render it temporarily conductive. Alpha, beta or gamma radiation, or any combination thereof, can be suitably selected and their sources appropriately arranged to cause optimum ionization of a gas, liquid or vapor, or any combination thereof. The specific ionization of alpha particles is greater than that of beta particles and alpha radiation may, therefore, be preferably used to ionize a gas or mixture of gases where the alpha particle range is sufficient. Gamma radiation has a long range, which introduces a difficult shielding problem in most cases. However, in those cases where large volumes of charged fluids are involved, use of gamma radiation would be optimum to ionize the large volumes since the gamma sources can be located at the centers of such volumes, for example.

FIG. 3 is a fragmentary front elevational view of the box spring assembly 82. Details of the assembly 82 are more clearly shown here. The lower base frame 96 supports the upper ground grid 98 on biasing springs 100 installed about the pendent pins 102. Blades 110 are secured to the lower part of base frame 96, and ground plates or bars 114 are welded between the sides of upper grid 98. The blades 110 normally cut into the upper surface of the grating frame 90 (FIG. 2C), and the upper surface of the upper grid 98 is held against shoulder ledge 62 (similar to that shown in FIG. 2A) of the upper pyramid 46 (FIG. 2D) with the upper grid suitably attached thereto for a positive ground contact.

FIG. 4 is a side elevational view, shown partly in section, of the box spring assembly 82 as taken along the line 4-4 indicated in FIG. 3. It can be seen that the pins 102 are fastened (threaded) at their upper ends to collars 122 of the upper grid 98 and to retainer nuts 108 at their lower ends. The biasing springs 100 are installed about the pins 102 and normally urge the nuts 108 to the tops of their respective channels 106. Blades 110 are located at the sides of the lower part of the base frame 96 as indicated. The box spring assembly 82 basically provides a good ground connection to the radioactive grating 84 (FIG. 2C) from the upper pyramid 46.

FIG. 5 is a graph showing plots of charge density versus fuel flow rate, which illustrate typical test results of the decharger 12 operating in the test rig setup of FIG. 1. Curve 124 is a plot of initial fuel charge as measured by the first charge density meter 30 after passing through the charge generating filter 28. Curve 126 is a plot of normalcharge retention by the fuel as measured by the second charge density meter 38 after passing through the bypass line 34. Curve 128 is a plot of the residual fuel charge as measured by the second meter 38 after passage through the decharger 12. Broken line 130 indicates a danger level being at 30 u-c/m and this level was achieved as intended by the decharger 12 in reducing an initial charge of 300 u-c/m to such level for a fuel flow rate of 600 gpm.

It is noted that the performance curve 128 was that of the decharger 12 including the charge extractor '72 therein. Tests made without including the extractor 72 in the decharger 12 showed that the extractor had only a negligible effect in achieving the residual charge. Any effect was, in fact, undetectable at the lower flow rates under 600 gpm. The charge extractor 72 is only effective at very high charge densities well in excess of 300 u-c/m", for example, and can be omitted from the decharger 12 for ordinary usage. The operation of the nuclear irradiator 40 is the main and essential factor in accomplishing the desired and necessary reduction of charge.

FIG. 6 is a central sectional .view of an illustrative, laminar ionizing, embodiment of this invention. A minimum size device 132 of relatively simple construction provides optimum use of radioactive material employed therein. The device 132-can be generally cylindrical in configuration and includes a length of steel pipe 134 having radioactive material 136 encased in a stainless steel sleeve 138 positioned concentrically within the pipe, and lead shielding 140 provided outside and in the ends of the pipe as shown. Flanges 142 are provided at the ends of the pipe 134 to permit easy connection in, for example, a fuel supply line (not shown). The pipe 134 is, of course, normally grounded as schematically indicated by ground connection 144. A needle extractor 146 generally similar to the charge extractor 72 (FIG. 28) can, if desired, be located just upstream of the radioactive sleeve 138.

Illustratively, the laminar device 132 can be approximately 34.0 inches long and 10.0 inches in (outside middle portion) diametenThe steel pipe 134 has an inside diameter of 6.0 inches and the lead shielding 140 on the pipe can be generally about 1% inches thick, for example. The radio-active sleeve 138 can be approximately 10.0 inches long and approximately 0.2 inch thick. The sleeve 138 can be a high integrity source of beta radiation provided by radioactive strontiummaterial and suitable for use in decharging Jet-A fuel flowing through it. For a nominal fuel flow rate of 600 gpm, at 300 u-c/m, the sleeve 138 can provide a level of radiation of about 900 curie s, for example, in the device 132 for reducing the charge to a safe level. The level of radiation provided can be reduced by a factor as large as 30 with improved and proper control of fluid flow wherein the radially inner core of fluid is suitably controlled to flow at substantially the same speed as the radially outer skin layer thereof.

In operation, it is assumed that electrostatically charged fuel flows into the left end of device 132 and out its right end. Any exceptionally high charge level in the fuel is reduced by the needle extractor 146. The

positively charged fuel has, of course, induced a nega-' the fuel flows over the radioactive sleeve 138, an adjacent laminar layer of fuel is rendered conductive so that the induced negative chargemoves onto the laminar layerQThis negative charge in the laminar layer is equal and opposite to the positive charge in the fuel core so that no further charge is induced on the pipe 134. The positively charged fuel core is mixed downstream with the negatively charged laminar layer of fuel on leaving the right end of the device 132 and is thereby neutralized. The thickness of the laminar layer of fuel can be, for example, of the order of about 5 to 10 millimeters (mm) for the illustrated device 132. Of course, if the fuel core is suitably controlled in device 134 by additional vanes or the like, so that the core s speed is close to that of the laminar layer of fuel, the thickness of the latter can be considerably less and, accordingly, a much lower level of radiation would be required.

Basic criteria for designing the static decharger, whether in a total volume irradiator embodiment or the equal but opposite charge embodiment, evolves from 9 the basic self-relaxation concept as expressed'in the following equation,

p p exp [K,t],

as the fluid conductivity 3, which is a factor in the constant K is directly proportional to the time of exposure t (i.e., inversely proportional to the fluid flow velocity).

Now, from the well-known continuity law,

-f a pear #1-ds=J gE-ds= jE-ds' v s s s where V is a given fluid volume, S is the surface enclosing the volume V, J is the current density at a point where the element of area 418 is located, and

E is the electrostatic field due to p. Therefore,

[SE-018* 1/t I ut kin where e is the permittivity of the fluid medium,

e, is the permittivity of free space, and

k is the dielectric constant of the fluid medium. Substituting Equation 4 in Equation 3,

-j p/anal (at) I per a 1 (slog EH! 5 By integration, then (P/PO) E p Helen] '10 case, it is desirable from a'design standpoint to have g approximately constant throughout the volume.

The conductivityg of the fluid in the linear approximation is g (n M n'M )e where n is the density of positive ions, n is the density of negative ions, M is the mobility of the positive ions (m /sec-volt in the MKS system), M is the mobility of the negative ions, and e is the basic unit of electrical charge (1.6 X l0- coulomb). It is assumed in Equation 7 that the ions are singly charged. Assuming, in ad dition; that n n and n -ln n, M" M and M M M, then g=enM Since the value of e is fundamental and M is a property of the fluid, the one factor in 3 that can be arbitrarily adjusted is n. Of course, the decharger works on an artificially introduced n much greater than A n (or An") where the An" (or An) is responsible for the charge on the fluid (fuel).

The density of ions, n, has been made large in the past by the addition of substances that ionize in the fluid (fuel), the so-calledanti-stat additives (which permanently alter the fuel). In my invention, n is increased by using high energy radiation to strip electrons from some molecules and deposit them on others. The most practical source of this radiation and radioactive material are, of course, used in this invention. The action of the radiation increases the value of n and is a temporary change since, for all practical purposes, the fluid is left unchanged.

The effect of increasing n and, hence, g is seen from Equation 6. Substituting Equation 8 into Equation 6,

(MP0) p ["(enM/ml liq. 9

Thus, a formal treatment yields Equation 9; however, for practical purposes, the fluid is not entirely surrounded by a' conductor nor is it practical to irradiate in such a manner because the object is to decharge the fluid and then pass it on and repeat the same to the following iluid.

Some valuable considerations in the static decharger can, howevenbe raised here in the context of Equation 9. First, t is the time over which the fluid volume is both at elevated n and in contact with a grounding element. flailing the average duration of t, for the root mean square as will be apparent later) averagely moving volume element, 1'.

Then, proportionately t as AL/F Eq.-l0

where F is the fluid flow rate, A is the mean cross sectional area, and t L is the average length of the radioactive element (width of grating strip elements 86 or length of sleeve 138, for example).

Second, n is the ion density produced by irradiation. in the case of non-uniform fluid flow (the usual case), it was seen that it should be nearly constant for ease of calculation. This means that the fluid should be uniformly irradiated, or a trade-off-between volume uniformity and surface irradiation should be made. Thus, the decharger design now must consider the range of the irradiation in the fluid. In the case of most liquids, beta radiationin the range of 0.5 to 1.5 million electron volts (Mev) average radiation energy is the most practical from the point of range in the liquid, penetration through the radioactive material encapsulation and minimizing the bremsstrahlung radiation against which shielding is most difficult.

Taking the foregoing considerations into account, the preferred (best) embodiment of the decharger accomplishing the process is a grating-like device where the ion recombination time is very short. It is very short, being approximately 0.1 millisecond for the n used in the decharger 12 (FIG. 1), but increasing as 1 /n In the static decharger, n is of the order of to l0 ions/cc, for example. Let, Y

n (DI/F) Dlt/A'L Eq. 1 l where D is the activity or number of radioactive disintegrations per unit time, I is the ionization or number of ions produced per disintegration, F is the flow rate of the irradiated fluid, and A' is the mean cross sectional area of the irradiated part of the fluid. As can be seen, I is a very critical number. There are a number of theories used and experiments conducted to try to predict and measure I. For the decharger 12, it was theoretically determined on one ion-pair per 100 ev of the beta radiation (or 50 ev per ion). Following actual construction of the decharger 12, however, it appearsmore in the range of 350 to 800 ev to produce an ion-pair.

Substituting Equation ll into Equation 9 and using r= r,

(1 /1 exp emblem/GA L exp [-eMDIAL/eAF] Eq. 12 Thus, Equation 12 is the basic design equation for the static decharger, The dependence on (t') or l/F is immediately seen. In practice, though, the relationship of F and I and D to form n is not so simple as given in Equation 1 1 because of recombinations but, or a rough approximation, Equation l2 works. For volume irradiation, a grating embodiment of suitable geometry appears superior. Of course, for volume irradiation, A A and Equation 12 becomes Eq. l3 Thus, in designing a volume decharger, the specific ge ometry employed is considered in practice and calculations are accordingly made. For example, to reduce 300 u-c/m to 30 u-c/m". (I /Pa) 0.1 and, for a given flow rate F, the product DAL can be used to determine the relative amount of radioactive material and dimensions desired.

FIGS. 7A and 7B are diagrams indicating the flow velocity profiles of fluids respectively having zero and some viscosity flowing through the radioactive sleeve 138. In F 16. 7A, for a zero viscosity fluid flowing in the sleeve 138, flow velocity F( y) is seen to be the same for all positions of y. This is the limiting case for a fluid of zero viscosity wherein there is theoretically no skin layer. Of course, this is physically unrealizable. in FIG. 7B, for a fluid having some viscosity flowing in the sleeve 138, it is seen that to be effective, the skin thickness Ay through which the conductivity is made larger (and quasi-uniform) must be thick enough wherein the radially inner velocity of the skin layer is up to that percentage of the mean flow velocity of the center core portion which is equal to the desired percentage of decharging. This, of course, puts a constraint on beta radiation range so that the mean ionizing range in the fluid of the beta particles must be approximately equal to Ay. In this case, where r is the inner radius of the sleeve 138,

With strontium-90, for example, maximum energy beta range is about 0.43 inch and mean energy beta range is about 0.15 inch. Thus, taking the weighted average of these ranges, Ay is equal to approximately 0.2 inch (which is half the spacing used between radioactive elements 86 of the grating embodiment).

Similarly, for the grating configuration, the range of the beta particles is the determinant of the spacing between the radioactive elements 86 (FIG. 2C). Thus, the ideal: spacing of the elements 86 (of 0.4 inch for L in Equation 11) is of the order- 080.4 to 0.5 inch ce nterto-center in the constructed decharger 1,2. This spacing is, of course that established by the strontium-90 beta particle range from the elements 86 in the fluid (fuel). The actual center-to-center spacing between elements 86 is, of course, 0.4 inch and this is desirable for producing a stronger field with the element width (L) of 0.4 inch. A larger spacing between elements 86 would make the elements 86 appear more like rods instead of plates. The closer spacing produces an apparently more uniform spacing between the parallel plane, ground potential, elements 86 and a minimum activity (curies) for adequate ionization would be required to produce an ion density much greater than that responsible for the charge on the fluid. As mentioned earlier, the criticality of keeping the radiation down but getting a sufficient number of ions is reflected in the value of I, the number of ions produced per disintegration. it makes all the difference between practicality and impracticality in that the value of 1 was sufficiently large and this constituted a significant discovery.

While certain exemplary embodiments of this invention have been described above and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of. and not restrictive on, the broad invention and that I do not desire to be limited in my invention to the specific details of construction and arrangements shown and described, for obvious modifications may occur to persons skilled in the art.

- I claim:

1. A process of reducing electrostatic charges in an electrically charged fluid, which comprises the steps of:

subjecting said charged fluid to ionizing radiation of predetermined intensity and ionization to render it conductive and elevated to at least a predetermined ion density for a predetermined time duration; contacting said charged fluid to grounded structure during said predetermined time duration; and

draining said charges in said charged fluid to ground through said grounded structure while said charged fluid is rendered conductive. 2. The invention as defined in claim 1 wherein said radiation is of predetermined characteristic range, and said grounded structure is of predetermined dimensions and includes radioactive material of predetermined activity, and further comprisingthe step of flowing said charged fluid at a predetermined rate through said grounded radioactive structure of predetermined dimensions whereby said charged fluid is subjected to said ionizing radiation to render it conductive and elevated to at least said predetermined ion density while passing through and contacting said grounded radioactive structure.

3. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising:

means for subjecting said charged fluid to ionizing radiation of predetermined intensity and ionization to render it conductive and elevated to at least a predetermined ion density fora predetermined time duration; and

means for contacting said charged fluid to ground and draining said charges in said charged fluid to ground while it is rendered conductive, whereby said charged fluid 'is decharged to at least a predetermined level.

4. The invention as defined in claim 3 wherein said radiation includes beta radiation with its characteristic range, and said contacting and charge draining means includes a conductive means for housing said charged fluid, and ground means connecting with said conductive housing means.

5. A. process of reducing electrostatic charges in an electrically charged fluid, which comprises the steps of:

subjecting said charged fluid to ionizing radiation to render a laminar layer thereof conductive; draining said charges in said laminar layer to ground while it is rendered conductive and leaving charges in said laminar layer equally opposite to the charges in the remainder of said charged fluid; and mixing said laminar layer with said remainder of said charged fluid to neutralize the same.

6. The invention as defined in claim 5 further comprising the step of flowing said charged fluid through a radioactive structure to subject it to ionizing radiation.

7. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising:

means for subjecting said charged fluid to ionizing radiation to render a laminar layer thereof conductive;

means for draining said charges in said laminar layer to ground while it is rendered conductive and leaving charges in said laminar layer equally opposite to the charges in the remainder of said charged fluid; and

means for mixing said laminar layer with said remainder of said charged fluid to neutralize the same.

8. The invention as defined in claim 7 wherein said fluid subjecting means includes a radioactive sleeve through which said charged fluid can be flowed and subjected to ionizing radiation to render a laminar layer thereof conductive.

9. The invention as defined in claim 8 further comprising a needle electrode, charge extracting means positioned upstream of said sleeve for reducing exceptionally high levels of electrostatic charges in said charged fluid prior to reaching said sleeve.

10. The invention as defined in claim 8 wherein said charge draining means includes a conductive means for mounting said sleeve therein and for housing said charged fluid, and ground means connecting with said conductive housing means, said sleeve being conductive and mounted in ground contact to said conductive housing meanswhereby said sleeve also serves as part of said charge draining means.

1 l. The invention as defined in claim 10 wherein said sleeve includes a radioactive material therein for providing a predetermined available activity and radiation range to produce said equally opposite charges in said laminar layer.

12. The invention as defined in claim 11 wherein said radiation range is correlated with flow of said charged fluid to provide a thickness of said laminar layer in which the inner velocity thereof is approximately equal to a predetermined percentage of the mean flow velocity of the central core portion of said charged fluid.

13. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising:

means for subjecting said charged fluid to ionizing radiation to render it conductive, said fluid subjecting means including a radioactive structure having a plurality of passageways through which said charged fluid can be flowed and subjectedto ionizing radiation to render it conductive; and

means for draining said charges in said charged fluid to ground while it is rendered conductive.

14. The invention as defined in claim 13 wherein said structure comprises a radioactive grating through which said charged fluid can be flowed and subjected to ionizing radiation to render it conductive.

15. The invention as defined in claim 14 wherein said grating includes elements having a selected radioactive material therein for providing a predetermined available activity and radiation range, said elements having a predetermined configuration and being arranged in a predetermined geometry in said grating to ionize the volume of said charged fluid passing through it.

16. The invention as defined in claim 14 further comprising a needle electrode, charge extracting means positioned upstream of said grating for reducing exceptionally high levels of electrostatic charges in said charged fluid prior to reaching said'grating.

17 The invention as defined in claim 14 wherein said charge draining means includes a conductive means for housing said charged fluid and ground means c0nnecting with said conductive housing means, said grating being conductive and mounted in ground contact to said conductive housing means whereby said grating also serves as part of said charge draining means.

18. The invention as defined in claim 17 wherein said grating includes a plurality of radioactive strip elements each having a generally rectangular plate configuration of predetermined length, width and thickness, said elements being positioned in parallel with their planes aligned generally with fluid flow direction and having a uniform spacing between said elements correlated to the mean range of said ionizing radiation.

Claims

1. A process of reducing electrostatic charges in an electrically charged fluid, which comprises the steps of: subjecting said charged fluid to ionizing radiation of predetermined intensity and ionization to render it conductive and elevated to at least a predetermined ion density for a predetermined time duration; contacting said charged fluid to grounded structure during said predetermined time duration; and draining said charges in said charged fluid to ground through said grounded structure while said charged fluid is rendered conductive.

2. The invention as defined in claim 1 wherein said radiation is of predetermined characteristic range, and said grounded structure is of predetermined dimensions and includes radioactive material of predetermined activity, and further comprising the step of flowing said charged fluid at a predetermined rate through said grounded radioactive structure of predetermined dimensions whereby said charged fluid is subjected to said ionizing radiation to render it conductive and elevated to at least said predetermined ion density while passing through and contacting said grounded radioactive structure.

3. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising: means for subjecting said charged fluid to ionizing radiation of predetermined intensity and ionization to render it conductive and elevated to at least a predetermined ion density for a predetermined time duration; and means for contacting said charged fluid to ground and draining said charges in said charged fluid to ground while it is rendered conductive, whereby said charged fluid is decharged to at least a predetermined level.

5. A process of reducing electrostatic charges in an electrically charged fluid, which comprises the steps of: subjecting said charged fluid to ionizing radiation to render a laminar layer thereof conductive; draining said charges in said laminar layer to ground while it is rendered conductive and leaving charges in said laminar layer equally opposite to the charges in the remainder of said charged fluid; and mixing said laminar layer with said remainder of said charged fluid to neutralize the same.

7. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising: means for subjecting said charged fluid to ionizing radiation to render a laminar layer thereof conductive; means for draining said charges in said laminar layer to ground while it is rendered conductive and leaving charges in said laminar layer equally opposite to the charges in the remainder of said charged fluid; and means for mixing said laminar layer with said remainder of said charged fluid to neutralize the same.

10. The invention as defined in claim 8 wherein said charge draining means includes a conductive means for mounting said sleeve therein and for housing said charged fluid, and ground means connecting with said conductive housing means, said sleeve being conductive and mounted in ground contact to said conductive housing means whereby said sleeve also serves as part of said charge draining means.

11. The invention as defined in claim 10 wherein said sleeve includes a radioactive material therein for providing a predetermined available activity and radiation range to produce said equally opposite charges in said laminar layer.

13. Means for reducing electrostatic charges in an electrically charged fluid, said charge reducing means comprising: means for subjecting said charged fluid to ionizing radiation to render it conductive, said fluid subjecting means including a radioactive structure having a plurality of passageways through which said charged fluid can be flowed and subjected to ionizing radiation to render it conductive; and means for draining said charges in said charged fluid to ground while it is rendered conductive.

16. The invention as dEfined in claim 14 further comprising a needle electrode, charge extracting means positioned upstream of said grating for reducing exceptionally high levels of electrostatic charges in said charged fluid prior to reaching said grating.

17. The invention as defined in claim 14 wherein said charge draining means includes a conductive means for housing said charged fluid and ground means connecting with said conductive housing means, said grating being conductive and mounted in ground contact to said conductive housing means whereby said grating also serves as part of said charge draining means.