EP0032100A2 - High pressure and very high temperature ionized gas generator - Google Patents

Abstract

Ionized gas generator with homogeneous supersonic flow. This generator comprises unit modules (11, 12, 13, 14) comprising: - two coaxial electrodes (22, 23) of cylindrical shape, the downstream electrode (23) being open and traversed by the flow; - Means (30) for injecting a gas in vortices along planes perpendicular to the axis common to said electrodes, the gas thus injected passing through an electric arc (26) which thereby takes an elongated shape; - means (27) for initiating the arc (26) between the two coaxial electrodes (22, 23); - Means (35) for cooling the electrodes, the gas injection devices (30), the coupling chamber (15); - coils (44) creating, around the first upstream electrode (22), a magnetic field ensuring the displacement of the base of the arc (26) around the internal surface of said upstream electrode (22). Application to tests of thermal protection materials.

Description

The present invention relates to the production of ionized gas at very high temperature and very high pressure, by heating by means of electric arcs of high power in direct current. It is known, in particular in space techniques, to actually use such ionized gas generators to test and choose thermal protection materials for space vehicles whose trajectories include in particular a phase of rapid re-entry into the atmosphere, during which the external component parts of the vehicle are brought very quickly to temperatures of several thousand degrees.

• - La première famille de générateurs de gaz ionisé comporte, entre deux électrodes tubulaires coaxiales généralement en cuivre ou en alliage de cuivre, réunies par une chambre d'injection d'air, un arc électrique en courant continu qui s'allonge sous l'effet d'une injection d'air tourbillonnaire. L'air chaud à très haute température et très haute pression est détendu à travers une tuyère coaxiale aux électrodes de manière à produire un écoulement à très haute température et à grande vitesse. Des dispositifs auxiliaires permettent l'amorçage de l'arc, en général par une électrode de démarrage, et la rotation des pieds d'arc évitant la fusion des électrodes, par des bobines de champ magnétique.
• - La deuxième famille de générateurs concerne des générateurs constitués de plusieurs modules unitaires connectés par une chambre de couplage équipée d'une tuyère d'émission du gaz ionisé. Chaque module est par lui-même un générateur constitué d'une électrode sphéro-cylindrique en graphite et d'une électrode tubulaire coaxiale en cuivre ou alliage de cuivre, réunies par une chambre d'injection d'air en tourbillon. Un arc électrique éclate entre les électrodes de chaque module. L'air chauffé au niveau de chaque module passe dans la chambre de couplage puis est détendu à travers la tuyère dont l'axe est perpendiculaire au plan constitué par les modules, de manière à produire un écoulement à très haute température et à grande vitesse. Des dispositifs auxiliaires permettent l'amorçage des arcs, en général par des fils fusibles, et la rotation des pieds d'arc sur les électrodes en cuivre ou alliage de cuivre par des bobines de champ magnétique.

Generators are already known for heating air or other gases with one or more high-power direct current electric arcs. These generators belong to two main families which will be recalled here in broad outline:

• - The first family of ionized gas generators comprises, between two coaxial tubular electrodes generally made of copper or copper alloy, joined by an air injection chamber, a direct current electric arc which elongates under the effect injection of vortex air. The very high temperature and very high pressure hot air is expanded through a nozzle coaxial with the electrodes so as to produce a flow at very high temperature and at high speed. Auxiliary devices allow the ignition of the arc, generally by a starting electrode, and the rotation of the arc feet avoiding the fusion of the electrodes, by magnetic field coils.
• - The second family of generators concerns generators made up of several connected unit modules by a coupling chamber equipped with an ionized gas emission nozzle. Each module is in itself a generator made up of a sphero-cylindrical electrode in graphite and a coaxial tubular electrode in copper or copper alloy, joined by a vortex air injection chamber. An electric arc breaks out between the electrodes of each module. The air heated at the level of each module passes into the coupling chamber then is expanded through the nozzle whose axis is perpendicular to the plane formed by the modules, so as to produce a flow at very high temperature and at high speed. Auxiliary devices allow the arcing, generally by fusible wires, and the rotation of the arc feet on the copper or copper alloy electrodes by magnetic field coils.

The two families of generators are used to test the test pieces as follows.

The test pieces of material, introduced or previously positioned in the flow, are subjected to aerothermal conditions similar to those which will be undergone by the same material equipping the spacecraft during the atmospheric reentry phase. The test pieces of material introduced into the axis of the jet are generally of sphero-conical or sphero-cylindrical shape (so-called "breakpoint" tests). The test pieces of material previously positioned parallel to the axis of the jet are of parallelepiped shape (so-called "square tube" tests).

The performance obtained on a test piece of material depends on its shape and its position in the jet. In general, at generator isoperformances, the test specimens in the jet axis are subjected to more severe aerothermal conditions than those parallel to the jet axis, but with measurement results more difficult to use.

The performance of the first family of generators, developed mainly by the American Company "Union Carbide Corporation" and existing in multiple copies in a range of electric powers from a few hundred kilowatts to a few tens of megawatts, are rather oriented towards obtaining jets of ionized gas of very high pressures and relatively enthalpies moderate, these conditions being measured upstream of the throat of the nozzle.

The performances of the second family of generators, developed mainly by the American company "AVCO Corporation" and existing in some examples with a power of the order of ten megawatts, are rather oriented towards obtaining pressure jets moderate and very high enthalpy, these conditions are also measured upstream of the nozzle neck. Reference is usefully made on this subject to the communication made by Dicristina, Hoercher and Siegelman at the "Intersociety Conference on Environmental Systems" in San Diego (California) from 12 to 15 July 1976.

The preceding generators however have certain drawbacks linked to their performance and their possibilities of use for testing test pieces of material.

Although the generators of the first family have performances well suited to carrying out so-called "breakpoint" tests because of their operation at high pressure, a drawback for exploiting these tests results from the very inhomogeneous temperature distribution. in the nozzle outlet jet, resulting from the injection of vortex air; the test pieces are subjected to highly evolving aerothermal conditions, thus making it more difficult to operate these tests. Another disadvantage is the ignorance of the direct thermal radiation coming from the arc which heats the test piece of material and which consequently comes to be added to the convective heating of this same material by the flow of ionized gas proper.

With regard to the so-called "square tube" tests, the major drawback for their exploitation results from the very inhomogeneous distribution of the temperature in the jet, with moreover the vortex mechanical effects generated by the injection of air.

Generators of the second family have the major drawback of low performance in generating pressure, prohibiting a whole range of tests with test pieces placed in a configuration of the "breakpoint" type.

The present invention specifically relates to an ionized gas generator for the study of test specimens at very high temperature and very high pressure which makes it possible to combine the advantages specific to each of the two families of preceding generators, by allowing the production of ionized gas. at very high generating pressures and moderate enthalpies with a flow of homogeneous ionized gas and without direct radiation of the arc on the test piece of material to be tested.

• - deux électrodes coaxiales alimentées en haute tension sous au moins plusieurs milliers de volts, en cuivre ou alliage de cuivre, de forme sensiblement cylindrique creuse, situées l'une derrière l'autre, l'une en amont et l'autre en aval par rapport au sens de l'écoulement du gaz ionisé, l'électrode aval étant ouverte et traversée par cet écoulement ;
• - des moyens pour injecter un gaz, par exemple de l'air, en tourbillons selon des plans perpendiculaires à l'axe commun auxdites électrodes, dans la zone intermédiaire entre la première électrode amont et la deuxième électrode aval, le gaz ainsi injecté traversant un arc électrique qui prend de ce fait une forme allongée pouvant s'étendre depuis l'extrémité de l'électrode amont jusqu'à l'extrémité de l'électrode aval, laquelle est ouverte à son extrémité et débouche dans l'un des orifices d'entrée de la chambre de couplage ;
• - des moyens d'amorçage de l'arc entre les deux électrodes coaxiales ;
• - des moyens pour assurer le refroidissement des électrodes, des dispositifs d'injection de gaz, de la chambre de couplage ;
• - des bobines créant, autour de la première électrode amont, un champ magnétique assurant le déplacement du pied de l'arc autour de la surface interne de ladite électrode amont.

This ionized gas generator, of the type which includes a certain number of generators or unit modules associated with a coupling chamber equipped with a nozzle, is mainly characterized in that each of the unit modules comprises:

• - two coaxial electrodes supplied at high voltage at least several thousand volts, of copper or copper alloy, of substantially hollow cylindrical shape, located one behind the other, one upstream and the other downstream by relation to the direction of flow of the ionized gas, the downstream electrode being open and traversed by this flow;
• means for injecting a gas, for example air, in vortices in planes perpendicular to the axis common to said electrodes, in the intermediate zone between the first upstream electrode and the second downstream electrode, the gas thus injected passing through an electric arc which therefore takes an elongated shape which can extend from the end of the upstream electrode to the end of the downstream electrode, which is open at its end and opens into one of the inlet ports of the coupling chamber;
• - means for striking the arc between the two coaxial electrodes;
• - Means for ensuring the cooling of the electrodes, of the gas injection devices, of the coupling chamber;
• - Coils creating, around the first upstream electrode, a magnetic field ensuring the displacement of the base of the arc around the internal surface of said upstream electrode.

According to an original characteristic of the ionized gas generator according to the invention, the means for injecting the gas in vortices into each module consist of a pressurized gas supply chamber associated with a gas injection ring consisting of a part cylindrical metal pierced with orifices opening tangentially to the internal wall of the crown and uniformly distributed over this wall in the injection space between the upstream electrode and the downstream electrode.

This injection of gas in a vortex, combined with the use for each of the unitary modules of a high inter-electrode voltage of several thousand volts, leads to the production of elongated arcs which can extend from the end of the electrode. upstream to the end of the downstream electrode, which gives, compared to the known prior art, an original character to this association of several modules. These new characteristics make it possible in particular to eliminate the inhomogeneities of temperature and flow of the jet of ionized gas while working at temperatures of the order of 5000 ° C. and with pressures close to 100 bars, which corresponds to enthal mass magpies reduced by around 100. These orders of magnitude, never obtained until now in homogeneous flow, allow great ease of interpretation and reproducibility of tests on samples. These interesting results are naturally combined with one of the important advantages of the multi-modular structure of the generator, namely the fact of protecting the test sample from direct radiation from the arc.

In a preferred embodiment of the ionized gas generator object of the invention, the unit modules are four in number, and the coupling chamber consists of a hollow central part of spherical shape to which are connected so centered five cylindrical passages, namely the first four located in the same plane at 90 ° from each other, and in each of which opens the jet of ionized gas from one of the modules, and a fifth, perpendicular to the plane of the first four, and which carries the emission nozzle of the ionized gas jet from the generator.

• - la figure 1 montre une vue d'ensemble en élévation du générateur de gaz ionisé objet de l'invention ;
• - la figure 2 montre en coupe selon l'axe XY l'un des modules constitutifs du générateur de la figure 1 ;
• - la figure 3 représente dans le plan horizontal XY de la figure l, la chambre de couplage et les liaisons de celle-ci avec deux des modules diamétralement opposés.

Anyway, the invention will be better understood on reading the following description of an embodiment of the ionized gas generator, description which will be made, without limitation, with reference to Figures 1 to 3 below -joint, on which:

• - Figure 1 shows an overall elevation view of the ionized gas generator object of the invention;
• - Figure 2 shows in section along the XY axis one of the constituent modules of the generator of Figure 1;
• - Figure 3 shows in the horizontal plane XY of Figure l, the coupling chamber and the connections thereof with two of the diametrically opposed modules.

We see in Figure 1 schematically, the generator 1 consisting of a support 10 in four parts of cruciform arrangement. The generator itself consists of four modules 11, 12, 13 and 14 located all four in the vertical plane containing the axes XY and X'Y '; the modules are aligned two by two, namely on the one hand modules 11 and 13 which are vertical, and on the other hand, modules 12 and 14 which are horizontal. The previous four modules 11, 12, 13 and 14 are associated with a coupling chamber 15 also located in the plane of FIG. 1, and from which emerges, perpendicular to this same plane, a nozzle 16 gathering the overall gas flow ionized generated by the four generator modules. To this end, the gas heated and ionized by an electric arc produced in each module is collected at the level of the coupling chamber 15, then expanded through the nozzle 16 so as to produce a homogeneous and supersonic flow at very high temperature and at high speed, flow perpendicular to the vertical plane of Figure 1 which includes the axes of the four modules.

Referring now to Figure 2, we will describe in more detail the constitution of a unitary module. We see in Figure 2 the envelope 20 of the upstream electrode 22 and the envelope 21 of the downstream electrode 23. According to the invention, these two electrodes are substantially cylindrical and arranged in the same alignment along their common axis 24 In addition, the electrode 23 is pierced right through, which allows, as will be seen below, the injected gas to flow from one end to the other thereof. A chamber 25 separates the two upstream 22 and downstream 23 electrodes, a chamber into which the generator supply gas is injected, as will be seen below. A direct current electric arc 26 is struck in the space 25 between the end of the electrode 22 and the electrode 23 using an auxiliary starting electrode 27 which can in particular be of any known type. Under the action of the air injected into the chamber 25, and which flows towards the outlet of the hollow cylindrical electrode 23, the electric arc also expands and takes a very elongated shape characteristic of the generator object of the present invention.

The injection of gas into the chamber 25 is carried out as follows. The gas is injected, by any known system, at 17 into a supply chamber 28, which communicates with a gas injection ring 30 consisting of a metallic cylindrical part pierced with orifices opening tangentially to the internal wall of the crown and distributed uniformly on this wall in the injection space 25 between the upstream electrode 22 and the downstream electrode 23. In the example described in the figure, the injection holes in the crown are distributed in four planes 31, 32, 33 and 34 equidistant from each other and perpendicular to the common axis of the device 24.

According to the invention, a cooling circuit 35 supplied by the input 36 is located around the upstream electrode 22 between this electrode proper and its envelope 20. The cooling liquid circulating in these envelopes allows the electrodes to be cooled vigorously. during operation of the device. An identical structure also equips the downstream electrode 23 which is surrounded by a cooling circuit 38 supplied by the inlet 37 located in the electrode casing 21. In the marl way, the gas injection crown 30 is provided with its own water cooling circuit 40 inlet and outlet 41 in Figure 2 and consisting of a number of bores parallel to the common axis 24 of the generator and distributed over the circumference of the crown gas injection 30.

In the embodiment described in FIG. 2, the gas injection ring is, by construction, at the same potential as the downstream electrode 23. It was therefore necessary to provide a device for electrical and thermal isolation of this ring d injection 30 relative to the upstream electrode 22. This double thermal and electrical insulation consists of a nylon sheath 42 which provides electrical insulation and a ring of silicon nitride 43 which provides thermal insulation.

In addition, to avoid rapid wear of the internal surface of the upstream electrode 22, provision has been made to move the base of the arc 26 around the internal surface of this electrode 22 by means of a magnetic field produced at using a set of coiled wafers or solenoids 44 coaxial with the axis 24, movable parallel to this axis and traversed by a direct electric current.

The module of FIG. 2 is connected to the coupling chamber 15 by a connecting piece 46. The coupling chamber 15 itself is constituted by an external envelope 50 of copper or copper alloy, of cubic shape, in which is located an internal piece 51 in one piece and also made of copper or copper alloy comprising a spherical part 5la and five cylindrical parts 5lb connecting to the spherical part 51a. The first four of these cylindrical parts 51b are in direct communication with the downstream electrodes 23 of each module and the fifth opens directly onto the nozzle 16, as can be seen in FIG. 3. Also shown in dotted lines in FIG. 2 , the path of the cooling circuit 55 of the internal part 51 and of the cooling circuit 62 of the nozzle 16.

We will now describe in more detail, with reference to FIG. 3, the coupling chamber and its connections with the four unit modules. It is recognized in this FIG. 3, the connecting pieces 46 connecting the two modules 12 and 14 to the coupling chamber 15. In FIG. 3, the two other modules are not visible, the module 11 being in front of the figure and the module 13 showing, at the bottom of the chamber 15, only the end of its structure represented in the form of concentric dotted circles. The coupling chamber proper is constituted by an external block 50 of cubic shape and in which is hollowed out a cavity coated with an internal piece 51 of red copper or copper alloy, monobloc, consisting of a spherical part 5la connected to five cylindrical parts 51b of which only three are of course visible. in FIG. 3, centered on the respective axes 24 and 24 of the modules 12 and 14 and on the axis 24a of the nozzle 16. The internal arrangement of the block 50 is such that separators 53 and 54 delimit circulation paths for water by thin films such as 55 and 56 to cool the internal part 51. Pressurized water inlets such as 57, 58, 59 and 60 are provided to supply this cooling circuit. A pressurized water inlet 61 is provided to supply the cooling circuit 62 of the nozzle 16, the corresponding outlet being referenced 63. FIG. 3 also shows the electrode 22 of the module 12 as well as the electrode 22b of the module 14 also provided with their respective cooling circuits 38 and 39.

The generator which has just been described operates in the following manner: the various cooling circuits such as 38, 39, 41, 57, 58, 59 and 60 are initially supplied from a network of pumps and valves allowing the individual control of these circuits in pressures and flow rates, at values such that the differences between these pressures and the atmospheric pressure initially prevailing in the generator are small. During the next phase, the coils 44 producing the magnetic field are energized. A short circuit is then produced between the upstream electrode 22 and the end piece of the central rod of the starting electrode 27. The gas is then injected into the generator through the orifices located in the planes 31, 32, 33 and 34 with regard to the module shown in Figure 2; then the current of the electric arc is established while eliminating the short circuit between the upstream electrode 22 and the end piece of the central rod of the starting electrode. When the central rod of the starting electrode has completed its displacement corresponding to the elimination of the short-circuit, the arc 26 of each module is transferred between the two electrodes 22 and 23 and becomes al lanyard under the effect of vortex gas injection. Stable and reliable operation is then obtained, resulting from the constancy of the parameters arc current, gas flow rate and the enslavement of the pressures in the cooling circuits to the pressure prevailing in the generator, thus minimizing the mechanical and thermal stresses. on the electrodes 22 and 23, the gas injection chamber 30, the internal part 51 of the coupling chamber 15 and the internal part of the nozzle.

• Servitudes électriques : quatre alimentations pouvant délivrer chacune 1.500 A sous 7.000 V, ou 3.000 A sous 3.500 V.
• Servitudes d'alimentation en eau : trois pompes d'alimentation pouvant délivrer chacune 40 1/s sous 100 bars associées à des circuits de distribution par vannes pilotées. Servitudes d'alimentation en gaz : réservoirs à 420 bars de pression de stockage pouvant débiter 0,5 kg/s de gaz à ioniser par module à une pression maximale de 250 bars. Générateur : Obtention de conditions génératrices du jet de gaz ionisé, c'est-à-dire de pressions de l'ordre de 100 bars et des enthalpies massiques réduites de l'ordre de 100.

By way of example, and for one mode of implementation, the dimensions and performances of the electrical services producing the electric arcs, of the water supply services of the cooling circuits, of the gas supply services of the generator, of the generator itself are:

• Electrical services: four power supplies each capable of delivering 1,500 A at 7,000 V, or 3,000 A at 3,500 V.
• Water supply easements: three supply pumps each capable of delivering 40 1 / s at 100 bars associated with distribution circuits by piloted valves. Gas supply easements: tanks with 420 bars of storage pressure capable of delivering 0.5 kg / s of gas to be ionized per module at a maximum pressure of 250 bars. Generator: Obtaining conditions generating the jet of ionized gas, that is to say pressures of the order of 100 bars and reduced mass enthalpies of the order of 100.

Claims (3)

1. Ionized gas generator with homogeneous supersonic flow, of the type which includes a certain number of generators or unit modules (11, 12, 13, 14) associated with a coupling chamber (15) equipped with a nozzle (16 ) perpendicular to this plane, characterized in that each of the unit modules comprises: - two electrodes (22, 23) supplied with high voltage at least several thousand volts, coaxial copper or copper alloy, of substantially hollow cylindrical shape, located one behind the other, one upstream and l further downstream relative to the direction of flow of the ionized gas, the downstream electrode (23) being open and traversed by this flow; - Means (30) for injecting a gas in vortices along planes perpendicular to the axis common to said electrodes, in the intermediate zone between the first upstream electrode (22) and the second downstream electrode (23), the gas thus injected passing through an electric arc (26) which therefore takes an elongated shape which can extend from the end of the upstream electrode (22) to the end of the downstream electrode (23), which is open to its end and opens into one of the inlet orifices of the coupling chamber (15); - Means (27) for initiating the arc (26) between the two coaxial electrodes (22, 23); - Means (35) for cooling the electrodes, the gas injection devices (30), the coupling chamber (15); - coils (44) creating, around the first upstream electrode (22), a magnetic field ensuring the displacement of the base of the arc (26) around the internal surface of said upstream electrode (22). 2. Ionized gas generator according to claim 1, characterized in that the means for injecting the gas in vortices into each module (11, 12, 13, 14) consist of a chamber (28) for supplying air under associated pressure. to an air injection ring (30) consisting of a cylindrical metal part pierced with orifices opening tangentially to the internal wall of the ring (30) and distributed uniformly over this wall in the injection space (25 ) between the upstream electrode (22) and the downstream electrode (23). 3. Ionized gas generator according to any one of claims 1 and 2, characterized in that the unit modules (11, 12, 13, 14) being four in number, the coupling chamber (15) consists of a hollow central part (51) of spherical shape to which are connected in a centered way five cylindrical passages (51b), namely the first four located in the same plane at 90 ° from each other and in each of which opens the jet of ionized gas of one of the modules, and a fifth, perpendicular to the plane of the first four, and which carries the nozzle (16) for emitting the jet of ionized gas from the generator.

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