GB1605238A - Mixing device for introducing a second gas into a gaseous flow - Google Patents

Abstract

Transmission tubes parallel to the flow allow a first gas to pass through two plates perpendicular to the flow, the second gas being introduced into the gap between these two plates and leaving through injection holes pierced through the downstream plate. The invention applies to nitrogen and carbon dioxide power lasers. <IMAGE>

Description

(54) "MIXING DEVICE FOR INTRODUCING A SECOND GAS INTO A GASEOUS FLOW" (71) We, COMPAGNIE GENERALE D'ELECTRICITE S.A. a French body Corporate, of 54 rue La Boetie, 75382 PARIS CEDEX 08, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention concerns a mixing device for introducing a second gas into a gaseous flow.

It applies to the case where there is a flow of a first gas and where it is required to introduce in a second gas into that flow, so as to produce rapidly a homogeneous mixture.

A known solution consists in arranging in the flow of the first gas a succession of tubes arranged parallel to one another in a plane perpendicular to the flow, leaving between them gaps to allow the first gas to pass therethrough. The second gas is supplied to these tubes which are each drilled with a series of injection apertures along one of its generating lines on its downstream face in relation to the flow, through which apertures the second gas escapes and is mixed with the first gas.

That known solution does not always make it possible to obtain such a fast mixing as is required, more particularly in the case where the first gas is nitrogen excited by an electric discharge and where the second gas contains carbon dioxide which must be energized by molecular interaction with nitrogen before natural de-energisation of the nitrogen, so that the carbon dioxide thus energized may constitute the active medium of a laser.

The aim of the present invention is to provide an improved device for mixing two gases.

According to the invention, there is provided a mixing device for introducing a second gas into a gaseous flow comprising a first plate formed with a number of first transmission orifices; a second plate formed with a number of second transmission orifices corresponding respectively to the first transmission orifices; and a number of transmission tubes each forming a fluid-tight connection between a respective one of the first transmission orifces and the corresponding second transmission orifice to define a path, leading from the first plate to the second plate, for the gaseous flow, the second plate also being formed with injection orificies capable of directing a second gas introduced under pressure into the space between the first and second plates into the gaseous flow emerging from the second orifices.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a cross-section view through a carbon dioxide laser in which carbon dioxide is introduced into a nitrogen flow by a device of the invention.

Figure 2 shows an enlarged cross-section view through the plane A (in Figure 3) of the device shown in Figure 1, and Figure 3 shows an enlarged front view of the device shown in Figures 1 and 2.

Laser generators in which an electric discharge is produced in a first gas (nitrogen) flowing at very high speed and in which that first gas is mixed with a second gas (carbon dioxide) in an expansion chamber in which is arranged an optical resonant cavity, are known. The electric discharge has the effect of supplying the nitrogen with an excitation energy which is transferred to the carbon dioxide by molecular interaction at the time of the mixing. The rapid movement of the mixture in the expansion chamber ensures that it reaches the optical cavity before deenergisation of the carbon dioxide, thus enabling a stimulated light emission to take place in the optical cavity, that is, a laser emission.

Nitrogen molecules have three excitation modes: thermal rotational and vibrational.

When the nitrogen molecules and the carbon dioxide molecules mix in the expansion chamber, vibrationalenergy of the nitrogen is the only mode which can be utilised to produce, in the carbon dioxide, the reversal of population which gives rise to a high-power laster pulse. It is necessary, for this to be so, that the mixing of the two gases be in a thorough and homogeneous manner before a large proportion of nitrogen molecules are de-energized. The device of the invention makes it possible to ensure such a mixing particularly rapidly.

Referring to Figure 1, a gaseous flux laser generator comprises a cylindrical enclosure 1, at one end of which an injection nozzle 2 constituting an anode and connected to a voltage generator G by means of a resistor R, leads in. The nozzle 2 has its axial passage 3 connected to a nitrogen source under pressure and shown diagrammatically as SN. The nozzle also has an injection orifice 4 diverging towards the inseide of the enclosure 1. A device 200 for mixing carbon dioxide and helium with nitrogen is placed at the other end of the enclosure. This latter device is fed from a carbon dioxide and helium source SC and is more particularly described with reference to Figures 2 and 3. It is connected electrically to the other pole of the voltage generator G. It is formed with a number of transmission orifices such as 202 allowing the nitrogen to pass.

The enclosure 1 is connected by the transmission orifices 202 to an expansion chamber 6 provided with two mirrors 7 and 8 constituting an optical resonant cavity. The mirror 8 is semi-transparent and thus ensures a laser emission in the direction of the arrow F.

The widest end of the expansion chamber is kept at a very low pressure by discharge means constituted by pipes connecting the chamber to a vacuum enclosure SV, shown diagrammatically and having sufficient dimensions for the pressure to remain practically zero therein all the time while the laser generator is operating.

Such a laser generator operates as follows: Nitrogen introduced under pressure into the axial passage 3 of the nozzle 2 is injected at supersonic speed into the enclosure 1 by means of the injection orifice 4. By a suitable choice of the parameters of the generator, such as the length and the diameter of the enclosure 1, the speed and the entry rate of the nitrogen into that enclosure and the ratio between the total surface of the transmission orifices 202 and the cross-section of the enclosure 1, a "main" swirling flow of the nitrogen in the enclosure 1 occures. That flow is shown by the arrows 14 shown in continuous lines. It ensures a homogeneous spacing out of the electrical discharge set up between the anode 2 and the device 200 by means of the generator G.

A part of the nitrogen drawn away by the main flow then flows through the orifices 202, forming a secondary flow shown by arrows formed by discontinuous lines, and draws away the carbon dioxide and the helium injected by the device 200. The carbon dioxide is then energized as described hereinabove and produce a laser emission in the direction shown by the arrow F.

Referring to Figures 2 and 3, the mixing device 200 comprises an "upstream" plate 204.

made of brass, having a thickness of 2 mm and drilled with a number of circular "upstream" transmission orifices 202 having a diameter of 5 mm, arranged in a square network with a spacing of 6 mm.

It comprises, moreover, a "downstream" plate 206, made of brass having a thickness of 3 mm, parallel to the plate 204, leaving between the two plates an intermediate space which is 5 mm thick and drilled with a number of "downstream" transmission orifices 208 corresponding to the orifices 202.

The upstream plate 204 is situated on the same side as the enclosure 1 and the downstream plate 206 is situated on the same side as the expansion chamber 6.

The upstream and downstream transmission orifices are connected together by transmission tubes 210, also made of brass, having a circular cross-section and welded by their upstream ends in a fluid-tight manner to the edges of the upstream transmission orifices 202. The length of those tubes is equal to the distance between the upstream face of the upstream plate 204 and the downsteam face of the downsteam plate 206 and do not extend beyond any side of the device 200. Their outside lateral surface has the shape of a cylinder of revolution. The thickness of their walls is practically zero at both their ends. However, it increases, from the upstream end of a tube, to a constriction at 1.5 mm from that end and then decreased to the other end.

The inside diameter of the tube is 2.5 mm at the constriction. A nozzle enabling the injection of the nitrogen into the chamber 6 at a supersonic speed is thus provided.

The downstream plate 206 comprises a number of injection orifices which are of two types.

The first type is formed by injection annuli 212 formed, around the tubes 210, by the peripheral part of the downstream transmission orifices 208, whose diameter is 5.4 mm, and the tubes 210, which incidentally have a diameter of only 5 mm.

The second type of injection orifice is formed by a number of cylindrical injection apertures 214 having a diameter of 0.7 mm.

Each downstream transmission orifice is surrounded by a cluster of four injection orifices 214 equally spaced out at 900 from one another around the axis of that orifice and being inclined at 450 to the axis of the nearest transmission orifice 212. Those orifices 214 are drilled at an angle in such a way that the distance from the axis of each of these holes to the axis of the nearest tube 210 is 3.7 mm on the upstream face of the downstream plate and only 3 mm on the downstream face. The result of this is that the gas stream emerging from that orifice touches, almost as soon as it emerges, the annular stream emerging from the injection ring 212 and that it is directd towards the stream of nitrogen emerging from the tube 210.

The upstream pressure, that is, the pressure of the nitrogen in the closure 1, is preferably between 0.1 and several bars, for example 1 bar.

The injection pressure, that is, the pressure of the mixture of carbon dioxide and helium in the intermediate space between the plates 204 and 206, is preferably between 60% and 100% of the upstream pressure.

The downstream pressure, that is, the pressure in the expansion chamber 6, may be of the order of 10% of the upsteam pressure. In these conditions, the necessary distance from the downstream plate to obtain a practically homogeneous mixture is a few centimetres. It is less than 30% to 50% of that which would be required if the mixture of helium and carbon dioxide were injected by means of a succession of tubes arranged parallel to one another in a same plane perpendicular to the flow, leaving between them gaps suitably profiled to let the nitrogen pass, to allow it to assume supersonic speed. The described device consequently makes it possible to improve greatly the power of the laser emission.

WHAT WE CLAIM IS: 1. A mixing device for introducing a second gas into a gaseous flow comprising a first plate formed with a number of first transmission orifices; a second plate formed with a number of second transmission orificies corresponding respectively to the first transmission orifices; and a number of transmission tubes each forming a fluid-tight connection between a respective one of the first transmission orifices and the corresponding second transmission orifice to define a path, leading from the first plate to the second plate for the gaseous flow, the second plate also being formed with injection orifices capable of directing a second gas introduced under pressure into the space between the first and second plates into the gaseous flow emerging from the second orifices.

2. A device according to Claim 1, wherein the injection orifices are at least partly defined between the peripheral part of the second transmission orifices and the respective transmission tube in each case.

3. A device according to Claim 1 wherein the injection orifices are at least partly constituted by injection apertures separate from the second transmission orifices.

4. A device according to Claim 3, wherein the injection apertures are arranged in clusters each adjacent one of the second transmission orifices with the apertures of each cluster being spaced around that orifice.

5. A device according to any one of Claims 1 to 4, wherein the length of the transmission tubes is equal to the distance between the outwardly facing faces of the first and second plates.

6. A device according to Claim 5, wherein the transmission tubes are each shaped to form a convergent-divergent nozzle with the constriction of the nozzle being nearer to the first plate than the second plate.

7. A device according to Claim 6, including means for passing nitrogen through the transmission tubes and for exciting this gas by an electric discharge and means for supplying a mixture of carbon dioxide and helium to the space between the first and second plates.

8. Mixing device substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. distance from the axis of each of these holes to the axis of the nearest tube 210 is 3.7 mm on the upstream face of the downstream plate and only 3 mm on the downstream face. The result of this is that the gas stream emerging from that orifice touches, almost as soon as it emerges, the annular stream emerging from the injection ring 212 and that it is directd towards the stream of nitrogen emerging from the tube 210. The upstream pressure, that is, the pressure of the nitrogen in the closure 1, is preferably between 0.1 and several bars, for example 1 bar. The injection pressure, that is, the pressure of the mixture of carbon dioxide and helium in the intermediate space between the plates 204 and 206, is preferably between 60% and 100% of the upstream pressure. The downstream pressure, that is, the pressure in the expansion chamber 6, may be of the order of 10% of the upsteam pressure. In these conditions, the necessary distance from the downstream plate to obtain a practically homogeneous mixture is a few centimetres. It is less than 30% to 50% of that which would be required if the mixture of helium and carbon dioxide were injected by means of a succession of tubes arranged parallel to one another in a same plane perpendicular to the flow, leaving between them gaps suitably profiled to let the nitrogen pass, to allow it to assume supersonic speed. The described device consequently makes it possible to improve greatly the power of the laser emission. WHAT WE CLAIM IS:

1. A mixing device for introducing a second gas into a gaseous flow comprising a first plate formed with a number of first transmission orifices; a second plate formed with a number of second transmission orificies corresponding respectively to the first transmission orifices; and a number of transmission tubes each forming a fluid-tight connection between a respective one of the first transmission orifices and the corresponding second transmission orifice to define a path, leading from the first plate to the second plate for the gaseous flow, the second plate also being formed with injection orifices capable of directing a second gas introduced under pressure into the space between the first and second plates into the gaseous flow emerging from the second orifices.

2. A device according to Claim 1, wherein the injection orifices are at least partly defined between the peripheral part of the second transmission orifices and the respective transmission tube in each case.

3. A device according to Claim 1 wherein the injection orifices are at least partly constituted by injection apertures separate from the second transmission orifices.

4. A device according to Claim 3, wherein the injection apertures are arranged in clusters each adjacent one of the second transmission orifices with the apertures of each cluster being spaced around that orifice.

5. A device according to any one of Claims 1 to 4, wherein the length of the transmission tubes is equal to the distance between the outwardly facing faces of the first and second plates.

6. A device according to Claim 5, wherein the transmission tubes are each shaped to form a convergent-divergent nozzle with the constriction of the nozzle being nearer to the first plate than the second plate.

7. A device according to Claim 6, including means for passing nitrogen through the transmission tubes and for exciting this gas by an electric discharge and means for supplying a mixture of carbon dioxide and helium to the space between the first and second plates.

8. Mixing device substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.