US3278798A - Magnetohydrodynamic generators - Google Patents

Description

3,278,798 MAGNETOHYDRODYNAMIC GENERATORS Jean Fabre and Zicu Croitoru, Paris, France, assignors to Electricite de France (Service National), Paris, France Filed Mar. 25, 1964, Ser. No. 354,679 Claims priority, application France, Apr. 1, 1963,

3 claims. (cl. 315-411) The present' inyention relates to methods and devices for producing a strongly ionized gaseous stream and in particular an ionized gaseous stream intended to produce available electric current in a generator of the magnetohydrodynamic type.

The chief object of the 'present inventionfis 'to improve t the efficiency and uniformity of ionization in a magnetohydrodynamic generator.

The invention is concerned with a method of producing onincreasing the ionization of a gaseous stream, by the application of a succession of luminescent discharges or arcs, of relatively short duration in several localized zonesof said gaseousstream.

For producing or increasing the ionization of a gaseous` stream flowing through a conduit of a magnetohydrodynamic generator, we provide in said conduit, in lcombination, a series of pairs of ionization electrodes carried by the walls of said conduit and disposed in such manner that the discharge ends of every pair are located opposite each other inside said conduit in said gaseous stream, and means for applying between the feed ends of every pair, which are disposed outside lsaid conduit, voltage pulses, having `a sutficient amplitude to start discharges or arcs between the corresponding discharge ends.

'In a preferred embodirncnt the ionization'electrodes are disposed in such manner that the straight lines defined by the couples of discharge ends of every pair of said lelectrodes are substantially parallel to the direction ofl the magnetic field, generally provided in a magnetohydrodynamic generator, thereby providing for a given quantity of ionizing energy, a higher degree of ionization than when these straight lines make a substantial angle with said direction. Preferred embodiments of our invention will be hereinafter'described with reference to the appended drawings, given merely by way of example, and in which: FIG. 1 diagrammatically shows in perspective view an embo'diment of a conduit, belonging to a magnetohydrodynamic generator, through which flows a gaseous stream, this conduit being-made according to our invention;

FIG. 2fis a view similar toFIG. 1 corresponding to another embodiment of the invention; A

FIG. 3 shows an example of means for applying voltage pulses.

In FIGS. 1 and2, itflwill be supposed that a gaseous,

preferably hot, stream F fiows at high speedthrough a conduit 1 (for instance of square or rectangular cross section) made of an insulating material (for instance glass). This conduit belongs to a magnetohydrodynamic generator and is located in a substantially uniform magnetic field A 'H (for instance'pcrpendicular to the side walls 2 of conduit 1). T his conduit carries a series of pairs of collecting electrodes 3, 4 for collecting positive and negative electric charges, these electrodes being disposed with their v i faces parallel to the magnetic' field H and lto the direction 3118398 Patented Oct. `1 1, 1966 'ice . of the gaseous stream F, for instance on the side walls 5 of conduit 1. The electric voltage thus created is to be used in load resistors 10 shown in FIG. l, but not shown, i

in FIG. 2 in order to simplify it.

According to the present invention, ionization of gas- ,V eous stream F as it flows in conduit 1 is obtained or increased by producing a series'of luminescent discharges or arcs, of relatively shortduration, in several localized zones of said gaseous stream (conduit 1).

The discharges or arcs ionize the gaseous stream inside conduit 1 by producing on the one hand negative electrons and 'on the other hand positive ions. These electrons and ions diifuse through :the fluid stream and .tend to bedistributed therein in a substantially uniform manner if said localized zones are sufficiently close to one another. After some milliseconds, the negative electrons and -the positive ions recombine; however if the discharges or arcs are sufficiently frequent (for instance if .the frequency of repetition is higher than 1000 cycles per second), it is possible to obtain a substantially statistic equilibrium, thelnumber of on-electron pairs in a given volume remaining substantially constant inside a given volume, duringlthe operation of generator.

Furthermore, if the gaseous stream contains an easily ionizable substance, in particular an alkaline metal` such as cesium, in the powdery or vapor state fortinstance, the discharges or arcs ionize not only the gas of the gaseous stream but also said substance, thereby producing or increasing the ionizatio'n of the whole body of the gaseous stream with a satisfac-tory efficiency.

VAccording to the present invention, said ares' are produced by means of voltage'pulses having a sufficient ampli-.

tude to produce discharges or arcs' between the discharge ends 6a, 7a, or 8a, 9a of a series of pairs of vionization electrodes 6, 7`(FIGURE l) or 8, 9't`FIGURE' 2) whichV are distinct from the collecting electrodes 3, 4 andcarried 1,

by the side walls S (in the embodiment of FIGURE 1) or 2 (in the embodiment of FIGURE 2) of co'ndui',V 1. Said discharge ends of every pair of ionization electrodes are located opposite each other in the gaseous stream inside conduit l. Said voltage pulses are applied (means not shown) between every pair 'of input ends 6h, 711, or 8b, 9b located outside conduit 1.

The distance between the ionization electrodes of every pair is advantageously substantially equal to the distance between the walls .ofconduit 1 that carry said electrodes, whereby these clcctrodes do not protrude substantially inside conduit 1. If these electrodes protruded substantially they would be eroded by the generally hot gas flowing through said conduit. v

Thefrequency of repetition of the arcsis chosen in accordance with'the speed of recombination of ions and electrons. It may for instance average 1000 cycles-` per second.

Preferably, as illustrated in FIG. 2, the ionization electrodes 8 and 9 are disposed in 'such manner that the straight lines defined 'by -the couple of discharge ends 8a,

9a of every pair are` substantially parallel to the dir-'ecv tion of lthe `rlnagnetic'field H, thereby yproducingrfor a given ionizing energy, a more intensive 'ionization than when these lines make a substantial angle with said'direction, because the passage of the ionizing electric cur- V rent is easier in av direction parallel 'to the magnetic lfield than transversely to said direction. v

'pair agravos 'known per se, illustrated in FIG. 3. Such a device comprises:

(a) a first circuit, or charging circuit, consisting of a high voltage source 11 (advantageously common to all the circu'its for the different pairs of ionization electrodes) a capacitor 12 and a resistor 13, capacitor 12 being gradually charged by source 11 through resistor 13 during a first phase; and i (b) a second circuit, or discharge circuit, comprising, in addition to capacitor 12, a spark gap 14, this second circuit serving to feed the ends 6b, 7h or 8h, 9h of a of ionization electrodes 6, 7, or 8, 9, respectively. The ionized gaseous stream that flows between the discharge ends 6a, 7a or 8a, 9a of the electrodes closes the electric circuit between these discharge ends. When capacitor 12 has been charged, at the end of the first phase of operation, to a sufliciently high potential difference, a spark is produced in spark gap 14 and a discharge takes place between the ends 6a, 7a or 8a, 9a. This is the second phase of operation, which constitutes, with the first phase, a cycle of operation of the device.

IA new cycle (charging of capacitor 12 by the first circuit and discharging of said capacitor 12 by the second circuit with prodution of discharges at 6a, 7a or 8a, 9a) starts then again and so on, the capacitance C of capacitor 12 determining the duration of the discharges in the gaseous stream between the ionization electrodes, whereas the product CR (R being the resistance of resistor 13) determines the frequency of the discharges.

If it is' desired to obtain an ionization which is substantially uniform in space and in time inside conduit 1, i.e., a constant density of ionization in each mall volume of the fluid stream during operation, then the successive pairs of ionization electrodes should be located snfficiently close to one another and the voltage pulses should be produced with a frequency of repetition suiciently great -to obtain a substantially homogeneous and constant sta- `tistic distribution of the electrons and of the ions inside the conduit during operation.

It is thus possible to bring the electric conductivity of a gaseous stream intended to supply electric current in a magnetohydrodynamic machine (said stream consisting for instance of argon with 0.l% of potassium, under atmospheric pressure at a temperature of 2000 K.) to a value ranging from about ten to several hundreds of mhos per meter, for instance equal to about fifty mhos per meter. p

ATheI present invention permits the production or increase of the ionization of a gaseous stream.

We may also apply the invention to varying the mean conductivity of a gaseous stream. In order to obtain such a variation, the frequency of repetition of the discharges of arcs is varied by varying the frequency of repetition of the voltage pulses applied to the feed or input ends 6h, 7b or Sb, 9b of the ionization electrodes 6, 7 or '8, 9.

It is even possible to modulate the mean conductivity of a gaseous stream, by modulating the frequency of repetition of the discharges or arcs.

The present invention has, over prior methods and devices, many advantages in particular as follows:

First it permits the ionization of a gaseous stream in a simple and efiicient manner.

It permits the varying of the conductivity of a gaseous stream by varying the degree of ionization.

The ionization method and =means according to the present invention are therefore quite different from the prior methods and means, in particular from that disclosed in the U.S..Patent No. 3.080,515 issuedon March 5, 1963, to Edward Charles Kehoe according to which there is created, by means of a single arc, a single conductor localized at a given time and which is displaced along a conduit. VOn the contrary, according to the present invention, we produce an ionization distributed in the whole volume of gas, in particular in the whole of the conduit 1.of a magnetohydrodynamic generator.

It follows that, in the method and device disclosed by said U.S. Patent No. 3,0S0,5l5, the electrodynamic forces are exterted on a thin slice of gas whereas, according to the present invention, the electrodynamic forces are distributed throughout the gaseous volume, in particular conduit 1. As a consequence, for a given flow rate and for a given extracted power, the length of a magnetohydrodynamic generator according to the present invention may be shorter than that of a generator made according to the U.S. Patent No. 3,( )80,515. The reduction of length of the conduit and the other advantages of a ionization distributed in a substantially uniform mannerthroughout the volume owing to the present invention are veryimportant from a technical point of view, in particular the heat losses along the walls are reduced when the length of the conduit is shorter.

In a general manner, while we have, in the above description, disclosed what we deem to be practical and efficient embodiments of our invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of our invention as comprehended within the scope of the appended claims.

What we claim is:

1'. In a magnetohydrodynamic generator:

an elongated conduit made of an electrically insulating material and adapted to be traversed by a hot gaseous stream containing constituents ionizable in positively and negatively charged fragments;

means for producing inside said conduit a substantially uniform magnetic field substantially perpendicular to the longitudinal direction of said elongated conduit;

a plurality of pairs of substantially flat collecting electrodes secured against the inside wall of said conduit, the two collecting electrodes ofeach pair being disposed in a confronting position with the flat surfaces thereof substantially parallel to the longitudinal direction of said elongated conduit and to said magnetc field, and being connected, outside said conduit, through a utilization load;

a plurality of pairs of substantially elongated ionization electrodes carried by and traversingthe wall of said conduit, and electrically insulated from said collecting electrodes, each of said ionization electrodes having a discharge end located inside said conduit and a feed end located outside said conduit, the discharge ends of the two ionization electrodes of each pair being disposed in a confronting position, with the direction of the straight line connecting said discharge ends of the two ionization electrodes being substantially perpendicular to the longitudinal direction of said elongated conduit;

and means for applying in operation, between the feed ends of the two ionization electrodes of each pair, voltage pulses having a suflicient amplitude to produce aros between the discharge ends of said two electrodes through said gaseous stream flowing in operation through said conduit in the longitudinal direction thereof. i

2. A magnetohydrodynamic generator as claimed in claim 1, wherein the straight line connecting the discharge ends of the two ionization electrodes of each pair is substantially parallel to said magnetic field.

3. A magnetohydrodynamic generator as claimed in claim 1, wherein said discharge ends of said ionization ele c'trodes are substantially flush with the inside wall of said Conduit. i 1

I References Cited by the'Egeamlner- UNITED STATES PATENTS 2,487332' 11/1949 Hagen 313-161 x 3,171,oo 2/1955 wood ez 51. 313. 3x e 3.133,403 5/1965; nufwnz 313-231 6 FQREIGN PATENTS 106,899 3`/ 1939 Australia.

JAMES w. LAwRENcE, Pfimary Ex'gzminzr.

GEORGE WESTBY, Examner. S. D. SCHLOSSER, Assistant Exqmiher.

Claims (1)

1. IN A MAGNETOHYDYNAMIC GENERATOR; AN ELONGATED CONDUIT MADE OF AN ELECTRICALLY INSULATING MATERIAL AND ADAPTED TO BE TRANSVERSED BY A HOT GASEOUS STREAM CONTAINING CONSTITUENTS IONIZABLE IN POSITIVELY AND NEGATIVELY CHARGED FRAGMENTS; MEANS FOR PRODUCING INSIDE SAID CONDUIT A SUBSTANTIALLY UNIFORM MAGNETIC FIELD SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINAL DIRECTION OF SAID ELONGATED CONDUIT; A PLURALITY OF PAIRS OF SUBSTANTIALLY FLAT COLLECTING ELECTRODES SECURED AGAINST THE INSIDE WALL OF SAID CONDUIT, THE TWO COLLECTING ELECTRODES OF EACH PAIR BEING DISPOSED IN A CONFRONTING POSITION WITH THE FLAT SURFACES THEREOF SUBSTANTIALLY PARALLEL TO THE LONGITUDINAL DIRECTION OF SAID ELONGATED CONDUIT AND TO SAID MAGNETIC FIELD, AND BEING CONNECTED, OUTSIDE SAID CONDUIT, THROUGH A UTILIZATION LOAD; A PLURALITY OF PAIRS OF SUBSTANTIALLY ELONGATED IONIZATION ELECTRODES CARRIED BY AND TRAVERSING THE WALL OF SAID CONDUIT, AND ELECTRICALLY INSULATED FROM SAID COLLECTING ELECTRODES, EACH OF SAID IONIZATION ELECTRODES HAVING A DISCHARGE END LOCATED INSIDE SAID CONDUIT AND A FEED END LOCATED OUTSIDE SAID CONDUIT, THE DISCHARGE ENDS OF THE TWO IONIZATION ELECTRODES OF EACH PAIR BEING DISPOSED IN A CONFRONTING POSITION, WITH THE DIRECTION OF THE STRAIGHT LINE CONNECTING SAID DISCHARGE ENDS OF TWO IONIZATION ELECTRODES BEING SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINAL DIRECTION OF SAID ELONGATED CONDUIT; AND MEANS FOR APPLYING IN OPERATION, BETWEEN THE FEED ENDS OF THE TWO IONIZATION ELECTRODES OF EACH PAIR VOLTAGE PULSES HAVING A SUFFICIENT AMPLITUDE TO PRODUCE ARCS BETWEEN THE DISCHARGE ENDS OF SAID TWO ELECTRODES THROUGH SAID GASEOUS STREAM FLOWING IN OPERATION THROUGH SAID CONDUIT IN THE LONGITUDINAL DIRECTION THEREOF.

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