GB2271301A

GB2271301A - Atomising nozzle and filter

Info

Publication number: GB2271301A
Application number: GB9314804A
Authority: GB
Inventors: Stephen Terence Dunne; William Barrie Hart
Original assignee: DMW Technology Ltd
Current assignee: DMW Technology Ltd
Priority date: 1992-09-29
Filing date: 1993-07-19
Publication date: 1994-04-13
Anticipated expiration: 2013-07-19
Also published as: GB9220505D0; HK1001472A1; ZA937136B; GB9314804D0; GB2271301B

Abstract

The present invention provides a simple form of nozzle assembly for use in generating sprays from a fluid, which comprises a plate 1 having grooves 2 leading to the edge and another plate 10 which lies on plate 1, co-operating with it so that the grooves become liquid conduits. As shown, grooves 2 converge so that issuing liquid jets impinge on each other. Other configurations are illustrated. Other, preferably smaller, grooves 3 link inlet 4 with plenum 5 from which grooves 2 run. These grooves 3 act as filters so that the liquid, which in use passes up spigot 21 to aperture 10 and inlet 4 is freed from solids before it reaches grooves 2. <IMAGE>

Description

TITLE: ATOMISING NOZZLE AND FILTER The present invention relates to an atomising nozzle and filter, notably to one which produces a spray of fine droplets suitable for the administration of a medicament by inhalation.

BACKGROUND TO THE INVENTION: In our PCT Application No GB91/00433 we have described methods and devices for forming sprays of fine droplets from a fluid without the use of pressurised propellant gasses, notably for the formation of sprays of a fluid medicament which have a mean droplet size of less than 10 micrometres for inhalation by a user so that the droplets of medicament can penetrate into the lower lung. In our PCT Application No GB91/02145 we have described methods and devices by which the formation of such sprays can be optimised by inducing secondary flows in the stream of fluid when it passes through the nozzle aperture.

In the preferred form of such methods and devices, a metered dose of the fluid medicament is drawn from a reservoir into a pressure chamber by retracting a piston in a cylinder of a pump mechanism against the action of a drive spring. The piston or spring is latched or otherwise retained in the retracted, or cocked, position so that the metered dose is held at ambient pressure in the pressure chamber of the pump until it is discharged. When discharge is required, the piston or spring is released and the spring drives the piston forward, thus applying a rapid pressure rise to the fluid causing it to discharge through the nozzle aperture and form a spray of droplets.

The very fine droplets required for the application of a medicament to the lower lung are achieved by the use of fine aperture size nozzles and high pressures, typically with nozzle apertures of less than 20 micrometres and pressures in excess of 300 bar.

The nozzle apertures required to achieve such fine droplets can be formed in a number of ways, for example by punching a hole in a metal plate and part closing up the hole to achieve a fine aperture with a rough rim which causes the secondary flows in the fluid stream as it passes through the nozzle aperture. However, the techniques used to form the nozzle aperture either require accurate machining of components on a microscopic scale, which is expensive and time consuming; or do not give consistent results, leading to rejection of components during quality control assessment prior to use or to inconsistent operation of the device.

Furthermore, the need to be capable of enduring the very high pressure surge, typically as high as 600 bar, when the device is actuated requires the use of mechanically strong components. Again, this adds to the cost of the device.

In our PCT Application No GB91/02147 we have described a form of construction which incorporates an integral one way valve and filter in the nozzle assembly to prevent air being sucked into the device through the discharge nozzle when the piston is being retracted to draw the metered dose of fluid from the reservoir and to prevent blockage of the fine nozzle aperture by solid particles entrained in the fluid.

In a preferred form of such a construction a cylindrical plug is a push fit in a chamber immediately upstream of the nozzle orifice to provide an annular passage between the internal wall of the chamber and the radially outward wall of the plug. This annular passage has a radial dimension equal to or less than the nozzle aperture and thus provides a fine filter to remove solid particles which might otherwise block the nozzle aperture. The fine annular passage also imposes a flow restraint on the movement of fluid which is overcome by the high pressure generated when the piston is driven on its forward, or discharge, stroke to allow fluid to flow outwardly through the nozzle aperture.

The flow restriction, however, prevents fluid from flowing back into the device as the piston is retracted. This reduces the risk of contamination of the fresh fluid drawn into the pressure chamber from the reservoir with air or fluid from the nozzle assembly downstream of the plug.

Again, such a device must be manufactured from metal to be able to withstand the pressure surge as the device is operated and thus requires high precision machining of components which is expensive.

We have now devised a form of device and a method for its manufacture which reduces the above problems and is capable of being made with a high degree of accuracy at low cost.

SUMMARY OF THE INVENTION: Accordingly, the present invention provides a spray generating device comprising a nozzle assembly for forming the spray of droplets from a stream of fluid fed to it by a means for generating a flow of fluid, which nozzle assembly comprises: a. a first member having formed in a first face thereof one or more fluid inlet(s) adapted to feed fluid to one or more fluid outlet(s) located at an edge of the first member, the outlet(s) being configured so that a spray of droplets is formed by the fluid outlet(s) from a stream of fluid flowing through them; b. a second member secured upon the said first face of the first member and adapted to co-operate with the first member to provide one or more conduits each adapted to connect a said fluid inlet in fluid flow communication with a said fluid outlet, preferably the said second member co-operates with one or more channels formed in the said first face of the said first member to define the walls of one or more fluid conduits connecting said fluid inlet(s) to said fluid outlet(s); and c. means for connecting said fluid inlet(s) to said means for generating the flow of fluid.

It is preferred that the fluid flow conduits each incorporate one or more narrow bore portions which have transverse dimensions and a transverse cross-section which is less than that of the fluid outlet(s) and which act as filters to protect the outlet(s) against blockage by solid particles in the fluid. The narrow bore portions also provide a flow restriction in the conduits which act as one way valves of the type described in our PCT Application No GB 91/02147.

Preferably, the first member is a substantially planar member and the channel(s), fluid inlet(s) and fluid outlet(s) are formed in a face of said first member with the longitudinal axes of the channel(s) and of the inlet(s) substantially parallel to the plane of said face and the plane of the outlet aperture substantially normal to the plane of the first member; and the said second member is a second generally planar member which is preferably of substantially of the same plan shape and size as the first member.

The means for connecting the fluid conduits of said first member to the flow generating device is preferably provided by locating one or more of the fluid inlet(s) at an edge of the first or second members and providing means by which the first and/or second members can be mechanically connected to the flow generating device, for example by being a sealed push fit into the fluid outlet of the flow generating device. Alternatively, a third member can be provided which is secured to a second face of either the first or the second member and which is provided with a fluid conduit adapted to be put in fluid flow communication with the means for generating the fluid flow.For example, the third member can carry a spigot which is a push or other fit in the outlet to a pump mechanism of the type described in our PCT Application No GB91/00433 and which has a bore which communicates with the fluid inlet(s) in the first member.

The bore of the spigot can act as the cylinder of the pump mechanism in such a device.

The nozzle assembly of the invention can readily be formed as a laminated unitary construction from components which have had the appropriate channels, inlets and outlets preformed therein by laser, chemical etching, photo-resist or other surface engraving techniques well known in the microforming art to achieve simple but accurately reproducible components having substantially flat opposing faces. These components can be secured together by diffusion bonding, adhesion, welding, clamping or other suitable techniques for securing them together in sealing engagement, optionally with sealing rings or other sealing interfaces between the members by simple assembly techniques.

Accordingly, from another aspect, the present invention provides a nozzle assembly comprising: a. a first member, which is preferably substantially planar, having one or more fluid inlet(s) formed therein, one or more fluid outlet(s) formed at an edge of the said first member and preferably also one or more channels formed in a first face of said first member substantially parallel to the plane of said face, the channel(s) connecting the fluid inlet(s) with the fluid outlet(s) in fluid flow communication and preferably incorporating one or more narrow bore portions which are adapted to act as filters and one way valves; b. a second member, which is preferably substantially planar and of substantially the same plan shape and size as the said first member, located upon said first face of said first member and co-operating with said first member to provide, and/or to define with the said channel(s) where present in said first member, conduit(s) for connecting said fluid inlet(s) with said fluid outlet(s) in fluid flow communication; and c. means for connecting the fluid inlet(s) of said first member in fluid flow communication with a means for generating the fluid flow.

Preferably, the fluid inlets, the fluid outlets and the connecting channels are formed wholly in the first face of the first member and the second member is a cover member secured over said first face to provide the wall forming the conduits. However, the second member can be provided with part or all of the connecting conduits, as when the second member is provided with the channels and the first member provides the closing wall for those channels. Similarly, the second member can be provided with part of the inlets and/or outlets formed therein. For example, the first and second members can have mirror image halves of the inlets, outlets and conduits cut in the opposed faces thereof whereby securing them together forms the desired whole inlets, outlets and conduits.

For convenience, the invention will be described hereinafter in terms of a first member which has the whole depth of the inlets, outlets and channels formed in the first face thereof and the second member has a substantially flat face which provides a wall to complete the inlets, outlets and conduits.

The fluid outlet(s) act as the spray generating means of the nozzle assembly. These can therefore be simple fine bore orifices which can have rough, polygonal or other crosssections or edges, as described in our PCT Application No GB 91/02145, to form a spray of droplets from a stream of fluid passing through the outlet aperture. Thus, the aperture can have a triangular, squared or other regular or irregular polygonal shape, preferably having a maximum to minimum aperture dimension of from 2:1 to 10:1. The lip of the aperture can be rough, as when the aperture is formed by an electro-sputter erosion technique in which material is removed from the first member by striking an arc between the member and an electrode.However, it is preferred that the aperture have a sharp lip thereto over which the fluid flow changes direction sharply to achieve the secondary flow in the mainstream of the fluid flow. Typically, the change in direction will be equivalent to at least 5%, preferably from 10 to 30%, of the total flow changing direction through 900.

Preferably, the change in direction occurs sharply, notably within an axial distance of less than five, preferably less than one, diameters of the width of the flow. Such change in direction, or secondary flow, can also be achieved by forming the aperture with an axially inwardly directed lip as opposed to an externally directed lip, for example where the aperture diverges along the line of flow and has an equilateral triangular plan shape with its apex directed against the intended line of flow of the fluid through the aperture. Alternatively, two channels can intersect within the plan area of the first member to form a turbulent flow in a single channel leading to the fluid outlet aperture located at the edge of the first member.

Alternatively, the change in direction can be caused by forming a flap or partial obstruction to the aperture whereby at least part of the flow of fluid through the aperture is subjected to a sharp change in direction by the flap or obstruction. Such a flap or obstruction acts on from 10 to 80% of the effective cross-section of the flow.

Other forms of secondary flow generators are described in our PCT Application No GB 91/02145 and the subject matter of that application is incorporated herein by this reference.

Where the fluid outlet is formed so as to generate the spray by means of the secondary flow caused by the shape and configuration of the outlet, we have found that satisfactory sprays can be produced with flow generating devices which generate a pressure low as 25 bar where comparatively large droplets are required, for example from 30 to 150 micrometres mass median droplet size. However, when droplets with a mass median size of less than about 20 micrometres are required, it will usually be necessary to use a flow generating device which generates a pressure of at least 50 bar, typically 100 to 400 bar.

The droplet size will also be affected by the nozzle aperture size. Thus, in general we have found that it is desirable to use apertures with maximum transverse dimensions of less than 500 micrometres, for example 50 micrometres or less. Where fine droplet sized sprays are required, the maximum transverse aperture dimension is preferably less than 30 micrometres. Such dimensions corrspond to cross-sectional areas of from 5 to 2,500, eg 10 to 500, square micrometres . Where coarse sprays are required, the aperture size can be to 100 micrometres maximum transverse dimension.

As indicated above, the desired spray can also be formed by causing two or more jets of fluid to impinge upon one another or for a single jet to impinge on a fixed impinger.

In this case it is not necessary that the nozzle aperture cause any significant amount of secondary flow and a smooth lipped substantially circular, squared or rectangular aperture can be used. In order to produce an acceptable jet, it is preferred to use a flow generating device which generates a fluid pressure of from 50 to 400 bar and an aperture with a maximum transverse dimension of from 5 to 100 micrometres. Where two impinging jets are used, it is preferred that the line of flight of the jets include an angle of from 60 to 1500, preferably about 90 to 1200, at the point of impact and that the impact occur from 25 to 500, eg. from 30 to 100, micrometres from the plane of the edge of the first member at which the fluid outlets are located.

Where a jet of fluid strikes a fixed impinger, it is preferred that this be located in the line of flight of the jet at a point before the jet begins to break up into separate droplets, typically less than 1000 micrometres downstream of the fluid outlet and that the surface of the impinger be angled to the line of flight of the jet so that the impinger is self cleaning and does not retain a significant amount of fluid thereon. We have described a suitable form of such a self cleaning impinger in our PCT Application No GB 92/0668.

For convenience, the invention will be described hereinafter in terms of the use of two fluid outlets to form twin jets of fluid which impinge upon one another to form a spray of droplets.

The fluid outlets are fed with fluid under pressure from the fluid flow generating means via the fluid inlet and the conduits formed in the first member. The fluid inlet is conveniently provided by a simple circular or other shaped chamber in the first member which is in direct fluid flow communication with the flow generating device via inlets at the edge of the first member or via a spigot or other means by which the nozzle assembly is mounted on the flow generating device. As indicated above, this spigot can form part of the pump mechanism of the flow generating device and can be carried by a third planar member which is mounted on the opposed face of the first member to that carrying the second member. However, the first member could be formed with the spigot formed integrally therewith, for example as a metal or other tubular projection from the second face of the member.

For convenience, the invention will be described hereinafter in terms of a third member carrying the spigot protruding therefrom.

A single fluid inlet chamber in the first member typically receives all the fluid fed to the nozzle assembly and distributes it to the fluid outlet(s). If desired, the fluid inlet chamber can be elongated in one or more directions to assist uniform flow of the fluid to the fluid outlets. For convenience, the invention will be described hereinafter in terms of a single generally circular inlet chamber.

The inlet feeds fluid via one or more conduits to the fluid outlet(s). As stated above, these conduits are formed by etching, engraving or otherwise forming suitable channels in the face of the first member, for example by inserting fine wires or ablatable material filaments into the interface between the first and second members so as to form depressions in the opposed faces of the members and then removing or burning away the wires or filaments to form the channels and outlets. The channels will typically have a generally squared cross-section since they are in general formed by the removal of material uniformly across the whole width of the channel.

As stated above, it is particularly preferred than the channels have one or more portions which are narrower than the aperture of the fluid outlet so that these portions act as filters to prevent solid particles which might block the fluid outlets from reaching the outlet in a manner similar to the fine bore passages described in our PCT Application No GB 91/02147. Such a fine bore portion of the conduit preferably has cross-sectional dimensions which are from 10 to 80% of those of the fluid outlet. It is also preferred that the fine bore portion of the channel cause a pressure drop of from at least 0.5 bar in the flow of fluid through the portion of the channel so that the narrow bore portion inhibits withdrawal of fluid from the channel during retraction of any pump mechanism used to generate the flow of fluid through the nozzle assembly.Preferably, the pressure drop is the minimum required to prevent return flow of fluid and air from the nozzle to the flow generating device and yet does not deleteriously affect free flow of the pressurised fluid through the channels and the fluid outlet(s). The optimum flow restriction can readily be determined for any given case, but will usually achieve a pressure drop of from 1 to 3 bar or more.

Whilst the channels may communicate directly with a fluid outlet, it is preferred that the narrow bore portions of the channels be located between the fluid inlet and a plenum chamber which feeds fluid to the fluid outlets. Such a plenum chamber aids uniform distribution of the flow of the fluid to the outlets where more than one outlet is used, for example where two outlets are used to form two jets of fluid which impinge upon one another. The plenum chamber may also be configured so as to assist the formation of secondary flow in the fluid as it flows to the outlet(s), for example by incorporating curves or other wall configurations for causing swirling in the fluid flow.

The nozzle assembly finds use on a wide range of fluid flow generating devices, such as pressurised gas or aerosol type dispensers in which fluid is caused to flow out of a container by the expansion of a propellant gas. However, the nozzle assembly is of especial application in forming a spray from a flow of fluid generated by a manually operated pump mechanism, thus avoiding the use of a propellant gas.

It is particularly preferred that the pump mechanism be of the type described in our PCT Application NO GB 91/00433.

The nozzle assembly is mounted by any suitable means upon the outlet from the pressure chamber of the pump, for example by a screw, bayonet, push or other fit, and receives the metered dose of the fluid when the spring or other energy source is released and the pressure within the pressure chamber rises. Other forms of fluid flow generator may also be used, provided that they can achieve the required pressure rise to discharge the fluid through the fluid outlet(s) as a spray with the desired mass median droplet size.

As indicated above, the channels, the fluid inlet, the plenum chamber and the fluid outlets are all formed in one face of the first member, although the fluid inlet can extend through the thickness of the first member to communicate with the fluid flow generating means. Such a design readily lends itself to fabrication by selectively removing the necessary material from the required areas of the surface of the first member by etching or engraving techniques which can be accurately controlled to form the very fine features required for the present invention.Such techniques are known and used in the formation of channels and nozzle outlets in the manufacture of ink jet printer heads, see for example US Patent 4915718 and European Application No 0397441, and in general comprise the application of a mask to a photo-resist or chemically etchable material; sensitizing the material and removing the material in the required areas by application of a suitable etching material. Alternatively, the channels can be formed by burning away the material using a laser or by striking an arc between the member and an electrode. Other methods for forming the features on the surface of the first member may be used, for example milling or fine engraving of silicon, ceramic or metal plates.

Such techniques can be used to remove accurately controlled amounts of material from accurately defined selective areas of the surface of the first member to form, within reason, any desired shape of channel, fluid outlet or other feature.

Such techniques are especially applicable to planar surfaces and it is therefore preferred that the surface of the first member in which the features are to be formed is substantially flat. However, they may also be applied to curved or irregular surfaces so that the surface of the first member need not be flat if desired.

The components of the nozzle assembly for use in the present invention thus readily lend themselves to manufacture by such techniques from a wide range of materials which are conventionally used in such techniques, for example photoresist plastic, silicon, ceramics, metals. Such materials can be produced to a high degree of accuracy and are often strong enough to resist the stresses due to the high pressure rises imposed upon the nozzle assemblies without the need for supporting framework or other structures.

Furthermore, being substantially flat members, the first, second and third members can readily be secured to one another in sealing engagement. Thus, metal, silicon or ceramic plates can readily be bonded together by pressure welding or by diffusion bonding in which an interface of a suitable metal, for example gold, is located between the opposed faces of the member and bonding caused by the application of heat and pressure. Such diffusion bonding has the advantage that little distortion of the shape of the channels and other features in the face of the first member is caused, thus preserving the accuracy of the features once formed.

Alternatively, the first and second members of the nozzle assembly can be secured in position by the use of adhesives, conventional ultra-sonic or other welding techniques or by mechanically clamping the components together. If desired, sealing rings or gaskets can be located between the opposing faces to ensure a fluid tight seal. However, where the faces of the members are sufficiently flat, this will usually not be necessary and the adhesive or metal diffusion interface between the opposed faces will ensure an adequate seal.

If desired, the assembled nozzle assembly can be located within a supporting housing or the like to impart the necessary strength to the assembly to withstand the high pressures generated by the devices of our PCT Application NO GB91/00433.

The nozzle assembly of the invention thus offers a simplified design which does not required expensive and time consuming machining of components and which enables components to be made reproducibly to a high degree of accuracy and which can readily be assembled to give the nozzle assembly.

The invention also provides a method for producing a nozzle assembly for use in a spray generating device of the invention, wherein the fluid outlet(s), the fluid inlet(s) and the connecting channels are formed in the face of the first member by selectively removing material from that face; and securing a second member upon the said first member whereby the face of said second member opposed to said first member co-operates with the said fluid outlet(s), fluid inlet(s) and said channels to form the fluid flow paths for said nozzle assembly.

DESCRIPTION OF THE DRAWINGS: To aid understanding of the invention, it will now be described with respect to a preferred embodiment thereof as shown in the accompanying drawings, in which Figure 1 is a diagrammatic exploded perspective view of the nozzle assembly; and Figures 2 to 7 are diagrammatic cross-sections through the area of the first member of the nozzle assembly showing alternative forms of the fluid outlet.

DESCRIPTION OF THE PREFERRED EMBODIMENT: In the nozzle assembly of Figure 1, a first plate member 1 has a first set of two channels 2 in its upper face which debouch at one edge of the plate. The resultant apertures at the plate edge form two fluid outlets which will form two impinging jets of fluid angled at about 100 to 1200 to one another when fed with fluid. Preferably, the edge of plate 1 is indented at this point to provide a recess in the face of the nozzle assembly within which the two jets of fluid can impinge and form the spray of droplets. The lips of the mouths of the depressions 2 where they intersect the edge of the plate 1 are sharply formed and not rounded.

The face of plate 1 also carries a second set of channels 3, which are of smaller cross-section dimensions than the first channels 2. These act as the narrow bore portions linking a fluid inlet 4 cut through plate 1 with the first set of channels 2 and serve to filter out solid particles which might otherwise block the first channels and the fluid outlets. Typically, the second channels each have a crosssectional area which is approximately 10% or less of the cross-sectional area of each of the first channels 2, so as to give a pressure drop of about 10% of the applied pressure from the flow generating device, for example of from 0.2 to 25 bar, across the second channels. Typically, the second channels 3 will have at least one cross-sectional dimension which is about 50% of the corresponding dimension of the first channels.Since the channels are typically formed by removing a uniform depth of material from the surface of the first plate member, the channels will usually have a constant depth and variations in the dimensions or area of the channels is achieved by varying the width of the channels.

The second set of channels 3 debouch into a plenum chamber 5 cut into the top face of plate 1. If desired, the chamber 5 can be cut through the thickness of plate 1, but it is preferred to form chamber 5 within the thickness of plate 1 as shown. Chamber 5 is preferably configured so that the first channels 2 exit from opposed corners of the chamber 5 and a septum 6 of the material of the surface of plate 1 can be retained between the channels 2 to aid changes in direction of flow of fluid within chamber 5 and to direct the flow into the first channels 2.

A second plate member 10 is shown overlying but detached from the first plate member 1. When this second plate 10 is secured to the top face of plate 1 it provides the top faces to the channels 2 and 3 so that they form two groups of conduits which form the nozzle outlets 2 and the filter bores 3.

A third plate member 20 is also shown detached and underlying plate 1. Plate 20 carries a fluid inlet spigot 21 by which the nozzle assembly can be mounted on the outlet of a pump or other fluid flow generating device (not shown).

The spigot 21 has an internal bore 22 which is in register with the inlet 4 in plate 1 and can form part of the pump mechanism of the flow generating device as indicated above.

The exterior of spigot 20 can carry screw thread or other means (not shown) by which the spigot is secured to the pump or other flow generating means.

The plates 1, 10 and 20 can be formed from any suitable material, for example a photo-resist glass, ceramic or plastic or a metal, and the features in plate 1 formed by removing material from plate 1 in the desired locations by a conventional chemical etching process. Alternatively, the features can be formed by removal of material using a laser.

Since the features are formed on the exterior of a substantially flat member, there is no need for complex machining of components or assembly of sub-components.

The plate members present opposed substantially flat faces to one another and can readily be bonded or otherwise secured to one another using any suitable technique, for example by ultra-sonic welding, by adhesion or by clamping them together using a metal surround which is crimped into position.

In operation, fluid at pressure is delivered to the bore 22 of spigot 21, from which is flows through inlet chamber 4 in plate 1, through the filter channels 3 to the plenum chamber 5 and thence to the nozzle channels 2. The fluid exits from the two nozzle channels as jets of fluid which impinge on one another to form a spray of fine droplets.

By applying the fluid at a pressure of at least 40 bar to nozzle channels having a mean diameter of about 10 micrometres, droplets with a mean droplet size of less than 10 micrometres were produced.

The nozzle assembly could be manufactured repeatedly to close tolerances and samples of the nozzle assembly repeatedly performed to give the same droplets sized spray.

Accordingly, from a further aspect, the present invention provides a nozzle and filter assembly characterised in that it comprises: a. a first plate into which are formed: 1: a first group of channels having one end thereof located at the plate boundary; and 2: a second group of channels of equal or smaller size than said first group; and b. a second plate that sealingly engages said first plate so the surface of said second plate co-operates with the first group of channels in said first plate to form a first series of fluid outlets and with said second group of channels in said first plate to form a second set of fluid conduits having a cross-sectional size equal to or smaller than the said fluid outlets, whereby when a fluid is passed through said second group of channels they act as a filter to protect the first set of channels which act as spray forming fluid outlets; and c. means of connecting said two sets of channels.

Preferably the nozzle assembly is connected to means for supplying first set of channels with fluid.

In the alternative forms of plate 1 shown in Figures 2 to 7, the outlet to the channels 2 is modified so that the fluid issues from the outlets as a spray without the need for impingement of two jets of fluid. Thus, in Figure 2 the outlet 14 to channel 2 is formed as a tortuous bend to induce secondary flow as the fluid exits the channel 2. To achieve a spray of droplets with a mass median droplet size of about 5 micrometres, the fluid outlet by channel 2 is from 2 to 15, preferably from 3 to 8, micrometres square in cross-section.

In the alternative form shown in Figure 3, a flap 25 is formed at the mouth of channel 2 and the edge of plate 1 is cut away in the area 26 downstream side of the flap.

In the alternative shown in Figure 4, the channel 2 is formed with a knife edge entry 31 having a gap 33 of from 4 to 30 micrometres and channel 2 diverges from that knife edge entry at an included angle 34 of from 60 to 1500, preferably from 90 to 1200. In the modification shown in Figure 5, the knife edge 41 is formed at the exit to channel 2 at the edge of plate 1 and sufficient wall thickness 42 is retained between the edge of the plate and the plenum chamber 5 to ensure the rigidity and strength of the knife edge.

In the alternative shown in Figure 6, the side walls of channel 2 are radially indented to provide a series of projections 51, 52 into the flow of fluid through the channel which induce secondary flow in the fluid as is passes through the mouth 53 of the channel. Typically, with a channel having a maximum mouth cross-sectional dimension of from 5 to 20 micrometres, the projections 51 and 52 will be from 3 to 8 micrometres.

In the modification of the device of Figure 1 shown in Figure 7, a septum 60 is formed within the plenum chamber which is separated from the wall of the chamber to provide two passages 61 and 62 which form two impinging flows of fluid in a swirl chamber 63 which debouches into a single outlet channel 2 to provide the secondary flow to form a spray as the fluid exits the mouth 64 of channel 2.

As indicated above, the depth and width of the channels formed in the first plate depend on the application of the nozzle assembly. For instance, when the nozzle assembly is used to spray hair sprays, the total cross-sectional area of the fluid outlet channels is typically 1500 square micrometres. If a single channel is used, this will be typically 40 microns deep by 40 microns wide. To achieve the required particle size of typically 40 micron mass mean diameter using such a nozzle assembly, fluid at a pressure of between 30 and 150 bars is used.

If the nozzle assembly is used to spray lung deposited drugs for administration by inhalation, then typically the total cross sectional area of the outlet channels 2 will be between 30 and 200 square micrometers. If a single outlet channel 2 is used, this will typically be 10 microns deep by 10 microns wide. The operating pressure required to achieve a spray with a mass median droplet size of less than 6 micrometres will be between 100 and 400 bars.

The nozzle assembly of the invention may be used in other applications where a simple, rugged device is required, for example in fuel injection systems for internal combustion engines, where a group of spray nozzles would typically be used either formed in one plate assembly or using a number of plate assemblies.

Claims

CLAIMS:

1. A spray generating device comprising a nozzle assembly for forming the spray of droplets from a stream of fluid fed to it by a means for generating a flow of fluid, which nozzle assembly comprises: a. a first member having formed in a first face thereof one or more fluid inlet(s) adapted to feed fluid to one or more fluid outlet(s) located at an edge of the first member, the outlet(s) being configured so that a spray of droplets is formed by the fluid outlet(s) from a stream of fluid flowing through them; b. a second member secured upon the said first face of the first member and adapted to co-operate with the first member to provide one or more conduits each adapted to connect a said fluid inlet in fluid flow communication with a said fluid outlet; and c. means for connecting said fluid inlet(s) to said means for generating the flow of fluid.

2. A nozzle assembly comprising: a. a first member having one or more fluid inlet(s) formed therein, one or more fluid outlet(s) formed at an edge of the said first member and one or more channels formed in a first face of said first member substantially parallel to the plane of said face, the channel(s) connecting the fluid inlet(s) with the fluid outlet(s) in fluid flow communication and incorporating one or more narrow bore portions which are adapted to act as filters and one way valves to the flow of fluid through the said channels; b. a second member located upon said first face of said first member and co-operating with said first member to define with the said channel(s) in said first member, conduit(s) for connecting said fluid inlet(s) with said fluid outlet(s) in fluid flow communication; and c. means for connecting the fluid inlet(s) of said first member in fluid flow communication with a means for generating the fluid flow.

3. A nozzle and filter assembly characterised in that it comprises: a. a first plate into which are formed: 1: a first group of channels having one end thereof located at the plate boundary; and 2: a second group of channels of equal or smaller size than said first group; and b. a second plate that sealingly engages said first plate so the surface of said second plate co-operates with the first group of channels in said first plate to form a first series of fluid outlets and with said second group of channels in said first plate to form a second set of fluid conduits having a cross-sectional size equal to or smaller than the said fluid outlets, whereby when a fluid is passed through said second group of channels they act as a filter to protect the first set of channels which act as spray forming fluid outlets; and c. means of connecting said two sets of channels.

4. A spray generating device or nozzle assembly as claimed in claim 1 or claims 2 or 3, wherein the fluid inlets, the fluid outlets and the connecting channels are formed wholly in the first face of the first member and the second member is a cover member secured over said first face to provide the wall forming the conduits.

5. A spray generating device as claimed in any one of claims 1 or 4, wherein the fluid flow conduits each incorporate one or more narrow bore portions which are adapted to act as filters to protect the outlet(s) against blockage by solid particles in the fluid.

6. A spray generating device as claimed in claim 5 or a nozzle assembly as claimed in either of claims 2 or 3, wherein the narrow bore portions impose a pressure drop of from 0.2 to 25 bar to the flow of fluid through said narrow bore portions.

7. A spray generating device or a nozzle assembly as claimed in any one of the preceding claims, wherein the first member is a substantially planar member and the channel(s), fluid inlet(s) and fluid outlet(s) are formed in a face of said first member with the longitudinal axes of the channel(s) and of the inlet(s) substantially parallel to the plane of said face and the plane of the outlet aperture(s) substantially normal to the plane of the first member.

8. A spray generating device or a nozzle assembly as claimed in any one of the preceding claims, wherein the means for connecting the fluid conduits of said first member to the flow generating device is provided by locating one or more of the fluid inlet(s) at an edge of the first or second members and providing means by which the first and/or second members can be mechanically connected to the flow generating device.

9. A spray generating device or a nozzle assembly as claimed in any one of claims 1 to 7, wherein there is provided a third member which is secured to a second face of either the first or the second member and which is provided with a fluid conduit adapted to be put -in fluid flow communication with the means for generating the fluid flow.

10. A spray generating device or a nozzle assembly-as claimed in any one of the preceding claims, wherein the fluid outlet(s) are configured so as to generate secondary flow in the fluid as it passes through the fluid outlet(s).

11. A spray generating device or a nozzle assembly as claimed in any one of claims 1 to 9, wherein there are at least two fluid outlets and they are configured so as to form at least two jets of fluid which impinge one upon the other.

12. A spray generating device or a nozzle assembly as claimed in claim 11, wherein the line of flight of the jets is to include an angle of from 60 to 1500.

13. A spray generating device or a nozzle assembly as claimed in any one of the preceding claims, wherein the fluid inlet(s) are in fluid flow communication with a plenum chamber which is in fluid flow communication with the fluid outlet(s).

14. A spray generating device or a nozzle assembly as claimed in claim 1 or in either of claims 2 or 3, substantially as hereinbefore described with reference to and as shown in any one of the accompanying drawings.

15. A method for producing a nozzle assembly as claimed in any one of claims 3 to 14 or for use in a spray generating device as claimed in any one of claims 1 or 4 to 14, wherein the fluid outlet(s), the fluid inlet(s) and the connecting channels are formed in the face of the first member by selectively removing material from that face; and securing a second member upon the said first member whereby the face of said second member opposed to said first member cooperates with the said fluid outlet(s), fluid inlet(s) and said channels to form the fluid flow paths for said nozzle assembly.

16. A method as claimed in claim 15, wherein said material is selectively removed by an etching process.

17. A method as claimed in either of claims 15 or 16, wherein the said second member is secured to said first member by adhesion, welding or diffusion bonding.