GB2300371A - Particulate dispenser - Google Patents

Abstract

There is disclosed a dispenser for generating an aerosol of, or finely dividing, a particulate material (1) from an agglomerated column of said material contained within the dispenser, wherein the dispenser comprises: i) a support (3) upon which, in use, one end of the column rests, the support (3) being provided with a plurality of perforations sized so as to allow passage of particles of the material (1) therethrough; and ii) at least one nozzle (6) adapted, in use, to direct a stream of gas into the column in the region of its supported end.

Description

PARTICULATE DISPENSER This invention relates to a method and apparatus for dispensing (or sorting) dry particulate for use in process technology; for production of research aerosols; and for producing aerosols or dispensing particulate for general use, including metered dose inhalation. The method and apparatus may also be used to dispense damp particulate if the gas used in the dispensing process has some drying action on that particulate.

General Aerosols Generation: At present most commercial aerosol dispensers (e.g. for cosmetics) use compressed high vapour pressure liquids such as CFCs as the carrier/propellant. If not, they generally use a pressurised liquid that is highly flammable. The active ingredient is often dissolved in the carrier liquid. These devices can be difficult to fill and pose a large environmental/safety problem.

Metered Dose Inhalers: Metered Dose Inhalers (MDIs) find many medicinal uses, such as the administration of medicaments to treat asthma and the like. The general disadvantages outlined above also apply here. At present many dispersal techniques are being researched and produced commercially. Most use mechanical movements within the particulate chamber to entrain the dry particulate into the gas stream. This has the disadvantage of requiring finely manufactured (and therefore expensive) durable parts, and can often produce an inconsistent output.

Inspiry-flow driven devices may get round this problem, but they can have an erratic performance due to their dependence on the rate of inspiration.

Most particulate used in inhalation therapy is hydroscopic, since it is required to dissolve in the fluid/blood in the lining of the lungs. Hence, humidity problems can cause particulate to stick together in devices such as these.

Research Aerosols Generation: At present the common method for producing research aerosol from dry particulate is to use a fluidised bed. Fluidised beds take a long time to settle down to produce a steady output at any single through flow-rate. The particulate tends to form into 'balls' between the jets of air. Fluidised beds normally use a layer of ball bearings to counter this effect and to form an impactor to stop the progress of large particles and agglomerations. Furthermore fluidised beds tend to be restricted to very low particulate outputs per time.

Process Technology: Most bulk particulate in chemical process technology is dispensed by hoppers or other mechanical dispensers. These are not very consistent in delivery, because particulate tends to stick to the hopper walls.

For this reason it is usually necessary to provide a means of vibrating the hopper.

The Invention: According to a first aspect of the present invention, there is provided a dispenser for dispensing dry particulate material from a column of agglomerated material including a support for the column, having a plurality of openings for allowing the passage of particles of the material there through, and at least one nozzle for directing a stream of gas across the supported end of the column and thence through the openings to release particles from the column and entrain them in the gas stream.

According to a second aspect of the present invention, there is provided a dispenser for generating an aerosol of, or finely dividing, a particulate material from an agglomerated column of said material contained within the dispenser, wherein the dispenser comprises: i) a support upon which, in use, one end of the column rests, the support being provided with a plurality of perforations sized so as to allow passage of particles of the material therethrough; and ii) at least one nozzle adapted, in use, to direct a stream of gas into the column in the region of its supported end.

According to a third aspect of the present invention, there is provided a method of generating an aerosol from, or finely dividing, a column of agglomerated particulate matter, wherein one end of the column is held against a perforated support and wherein at least one stream of gas is directed across the column in the region of said one end.

In a preferred embodiment, there is provided a plurality of nozzles which may be spaced around the support and directed generally inwardly. Means may be provided for urging the column and the support together.

Conveniently, the dispenser includes a container having a first open end through which the material forming the column can be inserted and a second open end through which the material is dispensed. The support, which may be in the form of a mesh or perforated plate, may extend across the container and is preferably proximal to the second end.

It is particularly preferred that the container be double-walled, in which case the nozzles may be formed in the inner wall and the gas may be supplied between the walls. The gas may be supplied from a pressurised gas cylinder or by a manually operated pump, where single-shot dispensing is required. If continuous dispensing is needed, a pumped gas supply may be provided.

The walls may be provided with baffles or the like projecting into the space therebetween to enhance heat transfer to the gas, for example, from the hand when the device is hand-held.

The gas stream, or streams, may simply skim the surface of the column which engages the support. More usually, it will enter the column immediately above the support. Conveniently, the gas stream or streams would initially be directed radially but a variety of gas streams may be appropriate for different purposes. For example, they may be fan-shaped or configured to set up a vortex or vortices.

The dispensed material may itself be entrained in a further gas stream for delivery to a remote point.

Although it is generally preferred that the support be relatively rigid, a flexible support may be employed, in which case the nozzle or nozzles may be located remote from the column and be adapted, in use, to direct one or more streams of gas through the mesh and into the particulate matter. The streams of gas will tend elastically to distort the support and will traverse across the column of material thereby serving to generate the required aerosol.

Preferred embodiments of the present invention use no moving parts within the particulate chamber in order to entrain the particulate in the airstream, and afford excellent disagglomeration. Particles are stripped away from the bulk particulate by the action of the gas. A uniform dose is easy to achieve because the same amount of gas may be throughput each time, at the same rate, causing the same amount of particulate to be stripped from the bulk mass.

Advantageously, the column of particulate material comprises alternating layers of a first, "active" material, and a second, "inert" material, the relative thicknesses of the layers and the gas control means being such that, upon actuation, substantially a complete layer of "active" material bounded on either side by a partial layer of "inert" material is dispensed. Each layer of "active" material may comprise a single measured dose of a medicament or the like, the intervening layers of "inert" material allowing for minor variations in the gas stream supply.

Preferably, the physical characteristics of the "active and "inert" particulate materials are the same or similar so as to avoid the generation of non-uniform turbulence on the column upon actuation of the dispenser.

The compressed gas may be released into the particulate by means of a valve from a pressurised container, or pressure-generated by hand or a gas compression machine.

The use of a gas such as CO2 as the carrier helps to counter humidity problems in the apparatus. If the particulate is tightly packed and permanently covered on all surfaces except near the mesh, humidity should only effect the layers near the mesh which may be in contact with the air or perhaps a person's breath. Air should be purged from the rest of the system by the gas, during the first few operations of the valve or other means of introducing the gas, and the gas should be retained for a while. In order to reduce humidity problems at the outlet of the column, the exit may be covered, for example with a cap, while not in use. The cap may advantageously contain desiccant, or may comprise a thin film which may be punctured or removed for operation of the device. Similarly, a shutter arrangement could be used, activated remotely or by the gas pressure.Another solution would be to use alternate layers of hydrophobic particulate placed between the layers of substance to be administered.

Use of a hydrophobic mesh may also reduce the possibility of wetting of the particulate.

Embodiments of the invention will immediately produce a steady output, which can be instantly varied by adjusting the flow rate. If the particulate is gravity-fed, and the gas is delivered through tubes in the walls instead of through an end cap arrangement at the particulate loading end, then the device can run for long periods of time with no maintenance or adjustment because it can be refilled continuously without significantly affecting the output characteristics. Larger output rates may be attainable than those achievable with fluidised beds.

Embodiments of the invention will disagglomerate the particulate and give a uniform delivery, making bulk processing in material processing industries more accurate. However, the mass delivery per time for some embodiments of the present invention, may be lower than that for a similar size existing processing instrument such as a hopper.

The apparatus can also be used as a separator (singularly or in multiple stages) for different size particulate. Smaller particulate is ejected while larger particulate is retained by the mesh. The mesh will tend not to be blocked by larger particulate because the gas passing through the particulate chamber will cause some turbulence and vibration so that larger particulate (assuming uniform density) will tend to move up the column.

The apparatus can be used in combination with other particle-influencing effects to select a required particle size fraction.

In addition, a number of dispensers together can be used for sequential (e.g. on a carousel) or combined dispensing.

Further advantages of embodiments of the present invention are easy filling of the active ingredient, and also that the particulate carrier can be supplied as a cartridge interchangeable with different gasproducing devices.

Where CO2 or similar is used as the propellant gas, relatively little environmental hazard will occur in comparison to systems which use volatile and/or ozonedestroying propellants.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which: FIGURE 1 shows a vertical section through a simple dispenser according to the present invention; FIGURE 2 shows the support mesh of the dispenser of Figure 1; FIGURE 3 shows a vertical section through an alternative embodiment of the present invention; FIGURE 4 shows the support mesh of the dispenser of Figure 3; FIGURE 5 shows a vertical section through a metered dose inhaler; FIGURE 6 shows a section through an alternative metered dose inhaler provided with sheath air and a hand-pumped priming device; FIGURE 7 shows a particulate dispenser or aerosol generator for process engineering; FIGURE 8 shows a research aerosol generator; and FIGURE 9 illustrates an alternative method of aerosol generation using a flexible mesh.

The apparatus described hereinafter can be used singularly or in multiple units.

A mass of particulate matter (1) is retained in a container (2) by a fine mesh (3) attached across an open end of the container (2). The particulate (1) is pressed onto the mesh (3) by an external force such as gravity, gas pressure, or a spring (4), pushing against the particulate (1) possibly via a follower (5). Gas is introduced under pressure through a series of holes or nozzles (6) at the mesh (3) covered end of the container (2), a short distance above the mesh (3).

Nozzles/holes (6) mounted in the container (2) wall at the perimeter of the mesh (3) are preferred, so that particulate (1) can continue to move freely towards the mesh (3). This arrangement helps to prevent the creation of a permanent cavern below a nozzle (6), such as may happen if the gas was introduced in a ring of nozzles (6) placed radially in the centre of the mesh (3). Preferably, the holes/nozzles (6) project the gas radially inward from the wall of the container (2).

The compression force ensures that the particulate (1) is continuously pushed towards the region where the gas enters the container (2) and is therefore continuously entrained in the gas. In this way, the formation of pathways permanently cleared of particulate (1) is avoided. Similarly, no permanent caverns are then created within the particulate (1) bulk. During operation some temporary pathways may be developed between the holes/nozzles (6) and mesh (3) by the gas travelling between these, but particulate (1) will be pushed into these pathways from the bulk particulate (1).

Particulate (1) is entrained by the gas as it flows between the holes/nozzles (6) and mesh (3) by the gas stripping off particles from the bulk. The particulate (1), when driven through the mesh (3), is subjected to high shearing forces, and will disagglomerate well. The holes/nozzles (6) may be covered with fine gauze to stop particulate (1) moving into them while the dispenser is not operating.

All the following examples possess the technical features described above. The designs and methods used for each example are interchangeable with the other examples.

The particular design specifications may be varied according to the required application. For the mesh (3), many materials and hole sizes can be used. For example, where it is desired to dispense 6ym alumina powder, a No. 50 US Mesh hole size metal sieve is suitable for good retention and shearing. A 25m holesize square weave steel mesh may also be used. With no gas emanating from the holes/nozzles (6), even if the mesh (3) hole size is considerably larger than the mean particulate (1) particle size, in many cases the particulate (1) will not significantly exit the mesh (3). This is due to cohesive forces present within the particulate (1), and adhesive forces between the particulate (1) and the mesh (3).

The particulate (1) does not easily exit even if the device is shaken vigorously, since by compression towards the mesh (3) the particulate (1) is hindered from reciprocal motion relative to the mesh (3).

The gas flow rate may be varied to suit the desired application. In many applications, a flow rate of 3 to 100 litres/minute is suitable.

For the gas pressure in the container (2) void, 2 to lOOpsi peak pressure is suitable for many applications. Gas may be introduced into the particulate (1) through any number of holes or nozzles (6). 12 holes (6) of 2mm diameter spaced evenly round the circumference of the inner wall of the container (2) may be provided. Use of any small nozzles (6) or other gas entry holes at the base of the particulate (1) column near to the mesh (3) will succeed in producing some particulate (1) output with gas flow through these nozzles (6). The preferred design for simplicity, cost, ease of construction and aesthetic appeal, is to use a double-walled container (2) with gas entry holes (6) drilled into the circumference of the inner wall. The void between the two walls is then pressured to achieve 'jets' of gas at the inlet holes (6).These jets of gas may be directed radially toward one another causing the resultant flow to be out of the device at approximately right angles to the initial trajectory of the jets.

Alternatively, the gas entry nozzles/holes (6) could be placed in the mesh (3) itself or could be angled in a more axial direction to allow higher output velocities. Furthermore, the nozzles (6) may be angled backwards away from the mesh (3) to produce lower output velocities, or indeed angled back from within the body of the mesh (3) or from just outside the mesh (3) i.e. outside the cylinder (2). The latter arrangement may improve the disagglomeration of the particulate (1). However, this arrangement may cause the gas-borne particulate (1) to deposit on the injection nozzles (6) due to the positions of the nozzles (6) in relation to the particulate (1) bulk and due to turbulence caused by injecting gas from these positions.

Example 1: There will now be described a general hand-held aerosol generator or particulate dispenser with specific reference to Figures 1 and 2.

A column of particulate (1) matter is retained in a double-walled cylinder (2) by a fine mesh (3) attached across an open end of the cylinder (2). The particulate (1) is pressed onto the mesh (3) by a helical spring (4) and follower (5). Other compression devices could alternatively be used, but it is preferred to use a spring (4) and follower (5) arrangement because, as gas is injected at the base of the particulate (1) column, the spring (4) may cushion forces acting upward towards the follower (5) or indeed allow the particulate (1) bulk to move away from the mesh (3) so that a more consistent degree of compaction may be maintained throughout the particulate (1) bulk.

This helps to avoid increasing compaction of the particulate (1) around the mesh (3) by sequential gas pulses during pulsed delivery operation, thereby maintaining a consistent output.

A bleed hole (not shown) may be provided at the end of the container (2) furthest from the mesh (3) so as to allow ambient or other gas to enter the container as the particulate (1) bulk moves towards the mesh (3).

This helps to prevent the generation of a partial vacuum as the particulate (1) bulk moves along the container (2). The top of the particulate bulk (1) may be sealed against these ambient or other gases by using a sealed plunger as a follower (5).

The particulate (1) column is first loaded on to the mesh (3), then the follower (5) and spring (4) are placed on the particulate surface. The end cap (C) is then screwed on, compressing the spring (4) and compacting the particulate (1) towards the mesh (3).

Gas entry holes (6) are installed in the inner wall of the container (2) near to the mesh (3).

A pressurised gas container (7) is mounted outside the particulate cylinder (2) by screwing to the end cap (C). When the gas container (7) is screwed on to the end cap (C), the pointed plunger (8) punctures the gas container (7) and gas is released to the valve (9).

This short-release valve (9) is opened manually. When the valve (9) is open, gas is introduced under pressure through a series of fine gauze-covered holes/nozzles (6) in the internal surface of the cylinder (2), a short distance above the mesh (3). Particulate (1) is entrained by the gas by way of stripping/pushing forces as the gas rushes between the holes/nozzles (6) and mesh (3). The gas/particulate (1) mixture is expelled through the mesh (3).

The mesh (3) needs to be rigid enough to retain a consistent position near to the pressurised air inlets (6) under the force of the spring (4) and follower (5), and to retain the size of its holes as gas/particulate (1) is driven through it. It could be a metal gauze with or without crossed beam supports, a perforated plate, a moulded plastic sieve, a sinter, or any other rigid mesh.

Where the nozzles (6) at the wall of the container (2) are configured to direct gas inwardly, the bulk of the particulate (1) column may tend to become supported by a central column of particulate (1) at the centre of the mesh (3), thereby leaving the zone near the nozzles (6) free of particulate (1). The severity of this effect depends on the action of the jets (i.e. whether vortices or the like are created). It may be preferable to use a shaped mesh (3) e.g. an inverted pyramid or 'V' which will push up and outwards from the centre of the column of the particulate (1) against the compression force applied to the column (1) (by spring (4), for example) thereby forcing particulate (1) towards the walls of the container (2) near the nozzles (6). A shaped mesh (3) may also direct the jets better to skim the mesh (3) and thereby more easily to entrain the particulate (1).

To hinder liquid, gas or water condensation droplets entering the particulate, a filtering device, mesh or series of baffle plates (10) may be installed within the container (2) walls. Baffle plates (10) help to warm the gas before it enters the particulate (1). Likewise, if only half the cylinder (2) wallspace capacity is expelled on each depression of the gas valve (9), a somewhat warmer gas should enter the particulate (1).

For particulate (1) of different diameter particle size or cohesive characteristics, the mesh (3) can be changed to one with a suitable hole size, along with changing the gas flow rate or pressure. For a given particle size and gas flow rate, the particulate (1) total output will tend to increase with increasing mesh (3) hole size, but so will the number of agglomerations present. The optimum condition of flow rate, velocity, nozzle (6) distance from the mesh (3), mesh (3) hole size and mesh (3) design can best be obtained by experimentation with the type of particulate (1) required to be dispensed.

Example 2: An alternative embodiment of the apparatus shown in Figures 1 and 2 shall now be described with reference to Figures 3 and 4. In this embodiment, the mesh (3) supporting the column of particulate (1), and also the column of particulate (1), is generally annular in shape. In other words, container (2) may be in the shape of a hollow cylinder (which may have a non-circular, e.g. oval cross-section). Nozzles (6) may be spaced around the mesh (3) end of the device, inside and outside the annular column of particulate (1), and be arranged to project gas outwardly from the inside of the column of particulate (1) and inwardly from the outside of the column of particulate (1).

This enables the particle (1) to be ejected from a relatively large diameter annulus, yet provides good particulate (1) disagglomeration due to there being a thin wall of particulate (1) "sandwiched" by jets of gas.

The advantages provided by these embodiments of the present invention over the prior art include: i) There is no use of CFCs or other acute environment damaging gases - no environmental hazard will occur, apart from a comparatively small release of CO2 for example.

ii) A constant mass output is easily achieved.

iii) Combustible gases need not be used.

iv) It is easier to fill containers with the active substance as a discrete particulate.

v) The particulate can be loaded as a pre-determined particle size for maximum target area deposition.

vi) The aerosol is easily delivered downwards.

This makes it easy to use an impactor or catch-pot type arrangement to discard agglomerations or impurities.

It also makes it easy to deliver particulate to horizontal surfaces; the aerosol can be delivered in other orientations but the output velocity may be lower in these orientations than with some conventional dispensers.

vii) The particulate carrier can be supplied as a cartridge interchangeable with different gas-producing devices.

viii)Particulate rushing through the mesh or air rushing through the particulate can generate static electricity, which may hinder the delivery of the aerosol to the desired target area. This effect, however, can be reduced by earthing the mesh/container by hand. The production of charged aerosol due to static is common with most dry particulate dispensers.

Notwithstanding the above, the production of charged aerosol may be beneficial in some instances. The mesh (3) may be allowed to become, or be deliberately, electrostatically charged by varying amounts in order to change the output characteristics of the device.

Example 3: A Metered Dose Inhaler (MDI) according to the present invention will now be described with reference to Figures 5 and 6.

A column of particulate (1) matter is retained in a double walled cylinder (2) by a fine mesh (3) attached across an open end of the cylinder (2). The particulate (1) is pressed onto the mesh (3) by a helical spring (4) and follower (5). Other compression devices could be used as an alternative.

The particulate (1) column is loaded on to the mesh (3), then the follower (5) and spring (4) are placed on the particulate surface. The end cap (C) is then screwed on, compressing the spring (4) and compacting the particulate (1) towards the mesh (3).

Gas entry holes/nozzles (6) are installed in the inner wall of the container (2) near to the mesh (3).

In the case of the device in Figure 5, a pressurised gas container (7) is mounted outside the particulate cylinder (2) by screwing to the end cap (C). When the gas container (7) is screwed onto the end cap (C), the pointed plunger (8) punctures the gas container (7) and gas is released to the valve (9).

This short-release valve (9) is opened manually. When the valve (9) is open, gas is introduced under pressure through the fine gauze-covered holes/nozzles (6) in the internal surface of the cylinder (2) a short distance above the mesh (3). Particulate (1) is entrained by the gas by stripping forces, as it rushes between the holes/nozzles (6) and mesh (3). The gas/particulate (1) mixture is expelled into the actuating nozzle (A), from which it is inhaled. Inhalation will need to be timed to coincide with the gas valve (9) release. An in-line actuator (A) is the simplest design and will minimise losses as the particulate (1) is expelled.

The actuator (A) may also be described as a mouthpiece. This may contain a trigger device (not shown) to activate the MDI during inhalation and to time the "firing" of the gas into the particulate (1) column to coincide with the inhalation.

To hinder liquid, gas or water condensation droplets entering the particulate (1), a filtering device, mesh or series of baffle plates (10) may be installed within the container (2) walls. Baffle plates (10), for example, would help warm the gas before inhalation. Likewise, if only half the cylinder (2) wall space capacity is expelled upon each depression of the gas valve (9), a somewhat warmer gas should be inhaled.

An alternative embodiment is shown in Figure 6 where the particulate dispenser is mounted in a sheath tube (ST) . When the patient breathes in, he uses his mouth to create a seal around the tube (ST) at the actuator (4), thereby creating a sheath of air (an annulus of moving air) which can improve the delivery of the aerosol bolus to the lungs during operation of the dispenser by enveloping that bolus into a relatively narrow trajectory. x means of blocking this tube (ST) until the particulate (1) is dispensed may be employed. For example, the gas injection device when primed may be in the form of an expanded balloon (BAL) which blocks the sheath tube (ST). Only when the gas in the balloon (BAL) is released into the particulate (1) column can the patient inhale through the device.

The walls of the sheath tube (ST) may restrict the expansion of the balloon (BAL) to the same size each time the device is primed. In this way the same volume of gas at the same pressure will be injected into the mesh (3) end of the particulate (1) column, thereby metering the same amount of particulate (1) each time the gas in the balloon (BAL) is released.

In Figure 6, the container (2) is single-walled and the gas is injected to the nozzles (6) via independent tubes (TU). The priming valve (VP) is a one-way valve that allows the balloon (BAL) to be inflated and independently to maintain this condition until the release valve (VR) is opened. The release valve (VR) may preferably be a device that, each time it is operated (triggered), opens to the same degree in the same time period. This means that the gas output velocity and volume flow rate will be the same on each operation of the valve (VR).

The balloon (BAL) is primed through the priming valve (VP) by pumping the plunger (PG) via the handle (HA) to displace the gas in the cylinder (CY) mounted in the carry tube (CT).

In addition to the general advantages provided by the present invention as set out above, these embodiments provide the following further advantages over conventional MDIs: i) The particulate/gas mixture will be expelled at low velocity from the actuator compared to conventional pressurised liquid MDIs because it does not emanate from a single small jet. This is an advantage because the aerosol can then follow the breathing streamlines into the lungs, instead of substantially impacting onto the back of the throat as happens with high velocity delivery. A sheathed gas flow may further assist the transport of the aerosol to the target area in the lung.

ii) The particulate can be loaded as a pre-determined particle size for maximum lung deposition. A large proportion of the aerosol from some compressed liquid MDIs is in large particle form, which impacts onto the throat, missing the target area.

As well as being a waste of active drug, this can become an irritant, for example when administering steroids, or cause problems due to ingestion. Some MDI systems use 'spacers' to combat the inhalation of larger particles.

iii) It is easier to measure the output particle size of the proposed device compared to most liquid MDIs because the output of these contains a complex of surfactant and propellant particles as well as the active drug particles.

iv) It is not necessary to add a larger sized particulate to help fluidise the mixture, though this may assist disagglomeration.

v) The same particulate carrier can be supplied as a cartridge interchangeable with different gasproducing devices.

vi) The device may be used as a simple MDI, where the individual doses are not prepackaged or mechanically separated. There need not be a "hard" barrier defining the extent of one dosage, but instead each dosage of particulate (1) may be "sandwiched" between two layers of similar but "inert" particulate.

Dispensing may thereby be more accurate and consistent.

Furthermore, minor leakage of particulate through the mesh (caused, for example, by external vibration) may therefore not substantially affect the magnitude of a subsequent dose.

Example 4: An embodiment of the present invention for use in process technology for dispensing or separating particulate will now be described with reference to Figure 7.

A column of particulate matter (1) is retained in a double-walled cylinder (2) by a fine mesh (3) attached across an open end of the cylinder (2). The particulate (1) is pressed onto the mesh (3) by its own and an additional weight (4) and possibly a follower (5) rested on the top of the particulate (1) column.

Other compression means, such as a spring or gas pressure, may be used.

With the particulate (1) and weight (4) inside the container (2), the end cap (C) is placed onto the cylinder (2) and held in place against rubber seals (R) by the use of clips (K). The compressed gas is introduced through a nozzle (N) on the end cap (C) and into the base of the particulate (1) column. The gas is introduced under pressure through a series of fine gauze-covered holes (6) in the internal surface of the cylinder (2) a short distance above the mesh (3).

Particulate (1) is entrained by the gas as it flows between the holes (6) and mesh (3). The particulate (1) is entrained in the gas by the effect of the gas stripping off particles as it rushes through the base of the particulate (1) column.

A metallic earth lead (L) may be attached to a suitable earth point in the working area so as to discharge the build-up of static electricity in the apparatus.

In addition to the general advantages provided by the present invention as set out above, these embodiments provide the following further advantages over conventional dispensers used in material processing: i) The output rate steadies quickly.

ii) The particulate becomes very finely divided, improving reactability, miscibility etc. with other materials used in processing.

Example 5: An embodiment of the present invention for use in research into particulate/aerosol generation will now be described with reference to Figure 8.

A column of particulate matter (1) is retained in a double-walled cylinder (2) by a fine mesh (3) attached across an open end of the cylinder (2). The particulate (1) is pressed onto the mesh (3) by its own and an additional weight (4) and possibly a follower (5) rested on the top of the particulate (1) column.

Other compression devices could be used, such as a spring, or gas pressure.

With the particulate (1) and weight (4) inside the container (2), the end cap (C) is placed onto the cylinder (2) and held in place against rubber seals (R) by the use of clips (K). Compressed gas is introduced through a nozzle (N) on the end cap (C) and into the base of the particulate (1) column. The gas is introduced under pressure through a series of fine gauze covered holes (6) in the internal surface of the cylinder (2) a short distance above the mesh (3).

Particulate (1) is entrained by the gas as it flows between the holes (6) and mesh (3). The particulate (1) is entrained in the gas by the effect of the gas stripping off particles as it rushes through the base of the particulate (1) column.

A metallic earth lead (L) can be attached to a suitable earth point in a room/working area so as to discharge the build-up of static electricity in the apparatus.

A conduit (T) around the cylinder (2) extending on the output side of the mesh (3) may be used for coupling to other apparatus or for producing a sheath air system to channel the particulate (1) output to improve delivery to the target. For example, by coupling the cylinder to an air ejector (E) as shown, this will produce suction at the output side of the mesh (3), increasing the output velocity, and will in addition create a sheath of air to channel the particulate (1) output into the centre of the output gas stream.

Radioactive sources or electric fields could also be used to control the amount of electric charge retained by the particulate/aerosol upon output.

In embodiments with low velocity outputs, it may be necessary to eject the output from the mesh (3) into an additional faster gas stream in order to project the particulate in directions other than downwards.

Example 6: Although a rigid mesh (3) is generally preferred, certain embodiments of the present invention may advantageously employ a flexible mesh (90) as shown in Figure 9. Such a mesh (90) combined with gas injected inward from outside the mesh (90) towards the container (2) may be a useful method of dispensing the particulate (1).

Claims (21)

CLAIMS:

1. A dispenser for generating an aerosol of, or finely dividing, a particulate material from an agglomerated column of said material contained within the dispenser, wherein the dispenser comprises: i) a support upon which, in use, one end of the column rests, the support being provided with a plurality of perforations sized so as to allow passage of particles of the material therethrough; and ii) at least one nozzle adapted, in use, to direct a stream of gas into the column in the region of its supported end.

2. A dispenser as claimed in claim 1, wherein there is provided a plurality of nozzles disposed around the support and directed generally inwardly.

3. A dispenser as claimed in claims 1 or 2, wherein means are provided for urging the column and the support together.

4. A dispenser as claimed in claims 1, 2 or 3, wherein the dispenser includes a container having a first open end through which the material forming the column may be inserted and a second open end through which the material is dispersed, and wherein the support extends across the container proximal to the second open end.

5. A dispenser as claimed in claim 4, wherein the container is double-walled, having an inner and an outer wall, the nozzle or nozzles being formed in the inner wall and gas being supplied, in use, between the walls.

6. A dispenser as claimed in claim 5, wherein baffles or the like project into the space between the walls of the container.

7. A dispenser as claimed in any preceding claim, wherein the nozzle or nozzles is or are adapted to generate a fan-shaped gas stream or streams.

8. A dispenser as claimed in any of claims 1 to 6, wherein the nozzle or nozzles is or are adapted to generate a vortex or vortices.

9. A dispenser as claimed in any preceding claim, wherein there is provided, in use, a further gas stream for entraining the dispensed material for delivery to a remote point.

10. A dispenser as claimed in any preceding claim, wherein the column of particulate material and the support are generally annular in shape.

11. A dispenser as claimed in any preceding claim, wherein there is provided control means for controlling the stream of gas such that, upon sequential actuation of the control means, a predetermined volume of gas at a predetermined pressure is directed into the column of material, thereby to dispense a predetermined quantity of material.

12. A dispenser as claimed in claim 11, wherein the column of material comprises alternating layers of a first, "active" material, and a second, "inert" material, the relative thicknesses of the layers and the gas control means being such that, upon actuation, substantially a complete layer of "active" material bounded on either side by a partial layer of "inert" material is dispensed.

13. A dispenser as claimed in any preceding claim, wherein the dispenser is annularly mounted in a sheath tube such that, upon operation, an annular stream of gas is generated in the sheath tube at and downstream of the dispenser, the annular stream of gas enveloping the material output from the dispenser.

14. A dispenser as claimed in any preceding claim, wherein the support comprises a relatively rigid mesh.

15. A dispenser as claimed in any preceding claim, wherein the support has a concave configuration.

16. A dispenser as claimed in claim 15, wherein the support is shaped so as to have a point which extends into the end of the column.

17. A dispenser as claimed in any of claims 1 to 13, wherein the support comprises a flexible mesh.

18. A dispenser as claimed in claim 17, wherein the nozzle or nozzles is or are located remote from the column and are adapted, in use, to direct one or more streams of gas through the mesh and into the particulate matter.

19. A method of generating an aerosol from, or finely dividing, a column of agglomerated particulate matter, wherein one end of the column is held against a perforated support and wherein at least one stream of gas is directed across the column in the region of said one end.

20. A dispenser substantially as hereinbefore described with reference to or as shown in the accompanying drawings.

21. A method of generating an aerosol substantially as hereinbefore described with reference to or as shown in the accompanying drawings.