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Title:
A NEBULISER
Document Type and Number:
WIPO Patent Application WO/2017/013072
Kind Code:
A1
Abstract:
A nebuliser comprising a reservoir of pressurised gas stored in a container; a reservoir of liquid; and a cyclonic nozzle to generate a nebulised flow of droplets of the liquid entrained in the gas. The nozzle comprises a conical mixing chamber having an axis, with a circular end face, an inlet for liquid from the reservoir, an inlet connected to the pressurised gas reservoir. The gas inlet is at the periphery of the circular end face and is directed to generate a swirl of gas about the axis. This generates a low pressure at the liquid inlet to draw liquid from the liquid reservoir into the nozzle. An outlet is located in the centre of the end face from which a plume of nebulised fluid is expelled.

Inventors:
CANNER PHILIP (AU)
Application Number:
PCT/EP2016/067068
Publication Date:
January 26, 2017
Filing Date:
July 18, 2016
Export Citation:
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Assignee:
LINDE AG (DE)
International Classes:
A61M15/00; A61M11/06
Foreign References:
US5596982A1997-01-28
US4333450A1982-06-08
US20030192532A12003-10-16
US5934555A1999-08-10
US20140343494A12014-11-20
US3989485A1976-11-02
Attorney, Agent or Firm:
CHRISTIE, Gemma (GB)
Download PDF:
Claims:
CLAIMS:

1 . A nebuliser comprising:

a reservoir of pressurised gas stored in a container;

a reservoir of liquid; and

a cyclonic nozzle to generate a nebulised flow of droplets of the liquid entrained in the gas, the nozzle comprising a substantially conical mixing chamber having an axis, with a substantially circular end face, a liquid inlet for liquid from the liquid reservoir into the nozzle, a gas inlet connected to the pressurised gas reservoir, the gas inlet being at the periphery of the circular end face and being directed to generate a swirl of gas about the axis to generate a low pressure at the liquid inlet to draw liquid from the liquid reservoir into the nozzle; and

an outlet in the centre of the end face, from which outlet a plume of nebulised fluid is expelled.

2. A nebuliser according to claim 1 , wherein the liquid inlet is at the bottom end of the cyclone chamber opposite to the circular end face.

3. A nebuliser according to claim 2, wherein the liquid inlet is displaced axially away from the bottom end towards the circular end face.

4. A nebuliser according to any preceding claim, wherein a hollow needle inserted in the bottom end provides the liquid inlet. 5. A nebuliser according to any preceding claim, wherein the maximum inner diameter of the mixing chamber is less than 3mm, preferably less than 2.5 mm and more preferably less than 2 mm.

6. A nebuliser according to any preceding claim, wherein minimum cross-sectional area of the gas inlet measured perpendicular to the direction of flow is less than 1 mm2, preferably less than 0.5 mm2 and more preferably less than 0.25 mm2.

7. A nebuliser according to any preceding claim, wherein the inner diameter of the outlet is less than 1000 μηι, preferably less than 800 μηι and more preferably less than 600 m.

8. A nebuliser according to any preceding claim, wherein the inner diameter of the liquid inlet is less than 500 μηη, preferably less than 250 μηη and more preferably less than 200 m.

9. A nebuliser according to any preceding claim, wherein the gas reservoir has a volume of less than 100 ml, preferably less than 80 ml and more preferably less than 60 ml.

10. A nebuliser according to any preceding claim, wherein the pressurised gas reservoir has a pressure of less than 500 bar, preferably less than 300 bar and more preferably less than 250 bar.

1 1 . A nebuliser according to any preceding claim, wherein the nebuliser is arranged such that each reservoir of pressurised gas is capable of nebulising at least 50 μΙ of the liquid, preferably at least 60 μΙ and more preferably at least 70 μΙ.

12. A nebuliser according to any preceding claim, wherein the nozzle is capable of producing the fine particle fraction of liquid of greater than 50% at 100 mm from the nozzle outlet.

13. A nebuliser according to any preceding claim, wherein the volume of the reservoir of pressurised gas, the pressure of the gas and the size of the outlet from the pressurised gas reservoir is such that, one opened, the reservoir will fully discharge in less than 3 minutes, preferably less than 2.5 minutes and more preferably less than 2 minutes.

Description:
A Nebuliser

The present invention relates to a nebuliser. The applicant is in the process of developing a nebuliser which can deliver an aerosolised plume of fine, respirable liquid droplets in a gas carrier to a location in which it can be inhaled by a user. It is intended that the nebuliser will not require a face mask or mouth piece but will provide a plume of which the user can inhale. The nebuliser includes a reservoir of pressurised gas, a reservoir of liquid to be aerosolised and an atomising nozzle. These elements may be multi-use, i.e. used on a number of occasions, or preferably single-use, i.e. used on a single occasion and then disposed of or recycled. Gas is to be supplied by a reservoir of pressurised gas stored in a container, usually referred to as a pressurised gas cylinder. There are a number of challenges in producing such a nebuliser. The plume must have a relatively high fine particle fraction (FPF) as, if there are too many larger droplets of the liquid, these cannot be inhaled and will be wasted. The target FPF of the present invention is greater than 50%, meaning more than 50% of the aerosolised liquid by mass is in droplets of a diameter of less than 5 μηη, at a location 100mm from the nozzle.

The gas reservoir, liquid reservoir and atomising nozzle are required to have a relatively small size in order to fit with the consumer's expectations of a single-use device, and in order to be cost effective for shipping and storage. On the other hand, they must be capable of generating a relatively high nebulisation rate over the period of use as it is estimated that approximately 75% of the available liquid will be lost either because it is generated while a user is breathing out or because the plume will not reach the user and is lost to the environment. The particular challenge is in minimising the size of the gas cylinder, as nebulisers typically require a high gas flow rate (and therefore volume of air), and existing widely available technology limits the upper pressure of the gas cylinders to around 200 bar.

As the atomising nozzle is intended to be suitable for single-use at a competitive price, it must be suitable for mass manufacture at a low part cost, for example by injection moulding. This limits the smallest dimensions in the nozzle to those that are achievable by standard low-cost mass manufacturing techniques.

It is intended that the nebuliser is a stand-alone unit without tethers, for example external power cables or pipes, and that it requires minimal user interaction, e.g. replacing of batteries. This restricts the possibility of electrical power or control electronics being used for the nebuliser.

A number of available nozzle technologies were evaluated to see if they were capable of meeting the above requirements.

Electronically powered atomisers such as vibrating mesh atomisers and Piezo atomisers were discounted as they require electrical power. Venturi atomisers which employ the Venturi effect to draw liquid into a fast-moving stream of air were evaluated. These typically use air pumps as a large volumetric flow rate of air is required and are not generally used with a reservoir of pressurised gas. They require a relatively high quantity of gas for the amount of entrained liquid, and so would be unsuitable for use in this application as the size of the pressurised gas reservoir would have to be too large to be marketable.

Swirl atomisers offer a better option for a device to be powered by a reservoir of pressurised gas, as small amounts of the high pressure gas could be used to drive the liquid through the nozzle. However, swirl atomisers generally produce droplets of a size too large to be respirable. The geometry of a swirl nozzle could be scaled down in order to bring the droplets into the respirable range, but the dimensions of the features of the nozzle would be too small to enable fabrication via standard mass manufacturing techniques such as injection moulding. Impaction pin atomisers are used in the automotive industry for diesel injection and in the environmental control industry for humidification purposes. These generally produce droplets which are too large to be respirable, although it has been suggested that smaller droplet sizes could be produced with a high enough pressure. The atomisers work by directing a liquid onto a fine pin head and using the impact energy to atomise the liquid jet. This impact removes a substantial portion of the liquid jet's momentum resulting in a broad and slow aerosol plume. The size of the spray orifice to achieve respirable sized droplets is likely to be tens of microns in diameter. This means that the pin must be very well aligned to achieve a consistent and reproducible aerosol so that it may be necessary to have multiple impaction pin nozzles in order to achieve the required delivery rate. We do not believe that this can be achieved at the cost that we require.

Liquid jet impingement atomisers work very well to produce droplets of the ideal respirable size range. However, the jets need to be very small to create sufficient velocity to produce respirable droplets as the jets impinge against one another. To achieve this, inhalers utilising jet impingement use a nozzle that is fabricated on a silicon wafer, which enables the precision necessary to produce fine jets that are perfectly aligned. Due to the manufacturing methods required, the resultant nozzle is likely to be too expensive to be commercially viable in this application. There therefore exists a need for a nebuliser with a low-cost nozzle which can operate with a low volumetric flow rate of gas such that a small pressurised gas reservoir can provide sufficient gas for the duration of use, while producing the required fine particle fraction and nebulisation rate of liquid. According to the present invention there is provided a nebuliser as defined in claim 1.

Such a nozzle uses a reverse flow cyclone geometry in order to draw in liquid from the reservoir by the action of the low pressure core generated by the swirling gas flow. The nozzle is capable of using only this negative gas pressure in order to entrain the liquid. Further, because of the nature of the reverse-flow cyclone, larger droplets will be retained within the cyclone until they are broken up such that they are small enough to enter the central core of the cyclone to be expelled. Because of this, the geometry can be arranged to provide the desired fine particle fraction without the need for further droplet size classification, e.g. by the use of baffles. The nozzle can generate very high shear forces and gas velocities within the cyclone chamber; this allows small droplet sizes to be achieved while keeping the dimensions of the inlets and outlet sufficiently large enough to enable the nozzle to be produced by existing injection moulding techniques such that this is a very low cost option. The high shear forces and gas velocities can be achieved at a comparatively low gas flow rate meaning that a small gas cylinder can be effective to nebulise a sufficient quantity of liquid. This means that a single small gas cylinder can be used for each use of the nebuliser.

The liquid inlet may be at the bottom end of the cyclone chamber opposite the circular end face, or may be displaced axially away from the bottom end towards the circular end face. In this case, a hollow needle inserted into the bottom end may provide the liquid inlet and may extend a significant axial distance away from the bottom end towards the outlet of the cyclone chamber. The distance of insertion of the needle can be fine-tuned in order to achieve the required liquid feed rate, as different insertion distances will place the tip of the needle in regions of different pressures.

The needle may be made as a separate component. This makes the manufacture of the rest of the nozzle simpler as the hole at the bottom end can be large in that it is sized to fit the needle, rather than being sized to provide the liquid inlet.

The needle may have a flat end (i.e. one which is coplanar with the end face).

Alternatively, it may be in a plane which is inclined with respect to the end face. As a further alternative, it may have an outlet orifice in the side of the needle rather than the end. This is preferably central within the cyclone chamber, but need not be in order to expose the end of the needle to the higher velocity spinning gas and higher shear forces. The needle may not necessarily enter through the bottom of the chamber, but may enter through some other part. The needle may be fixed or movable to allow the device to be tuned. The needle could be assembled into cyclone chamber by means of piercing an elastomeric septum that forms the base of the cyclone chamber. Alternatively, and amongst other methods of assembly, the needle could be co-moulded into the cyclone chamber, or bonded into place. The diameter and length and hence flow-resistance of the liquid inlet can be used to govern the flow of liquid entering the cyclone, as the cyclone will generate a fixed negative pressure at the opening of the inlet for a given gas flow rate.

As mentioned above, the low pressure generated by the swirling gas draws the liquid into the nozzle. However, to achieve higher liquid flow rates than might be drawn by this effect alone, it is possible that a pump for the liquid may also be provided to assist with the liquid flow or that gas from the reservoir might be diverted along a parallel path to be used in driving the liquid through the nozzle. The outlet may feature an annular wall extending inwardly and axially into the chamber. Such a wall, known as a vortex finder, will assist in preventing particles or droplets exiting the cyclone chamber prior to being classified. If the nebuliser has the needle, this may terminate short of the annular wall, or may extend up inside or through the vortex finder. There may be an inverted conical base at the bottom end of the chamber providing a vortex stabiliser. This minimises precession of the cyclone and helps ensure that the low pressure cyclone core remains directly above the liquid inlet.

The gas inlet may be in the form of a number of inlets spaced around the circular end face. However, in order to simplify manufacture, preferably it is a single inlet. The inlet may be a tangential, helical, or scrolled, in order to efficiently establish a swirling flow.

In order to achieve high gas velocities and the resulting high shear forces, while minimising gas consumption and manufacturing cost, the nozzle is intended to be a relatively small component subject to the constraints of the injection moulding process. A further advantage of a small cyclone chamber over a larger cyclone chamber is that the smaller cyclone chamber's droplet or particle classification performance is higher for a given driving gas pressure due to the reduction in the radius of the forced vortex and the consequent increase in the centripetal acceleration of the droplet or particle. Therefore, preferably, the cyclone chamber is as small as possible whilst being possible to mass manufacture at a low cost. Thus, preferably, the maximum inner diameter (i.e. the diameter adjacent to the circular end face) of the mixing chamber (excluding the gas inlet features) is preferably less than 3 mm, more preferably less than 2.5 mm and most preferably less than 2 mm. The minimum cross-sectional area of the gas inlet measured perpendicular to the direction of flow is preferably less than 1 mm 2 , preferably less than 0.5mm 2 and more preferably less than 0.25 mm 2 . In the case of multiple gas inlets, this value is the total value of the cross- sectional areas of the inlet added together.

The inner diameter of the outlet is preferably less than 1000 μηη, more preferably less than 800 μηη and most preferably less than 600 μηη. The inner diameter of the liquid inlet is preferably less than 500 μηι, more preferably less than 250 μηι and most preferably less than 200 μηι. The gas reservoir preferably has a volume of less than 100 ml, more preferably less than 80 ml and most preferably less than 60 ml. The pressurised gas reservoir preferably has a pressure of less than 500 bar, more preferably less than 300 bar and most preferably less than 250 bar. The nebuliser is preferably arranged such that each reservoir of pressurised gas is capable of nebulising at least 50 μΙ of the liquid, more preferably at least 60 μΙ and most preferably at least 70 μΙ.

The nozzle is preferably capable of producing the fine particle fraction (i.e. a fraction of particles greater than 5 μηι) of liquid of greater than 50% at 100 mm from the nozzle outlet.

Preferably, the volume of the reservoir of pressurised gas, the pressure of the gas and the geometry of the flow path is such that, once opened, the reservoir will fully discharge in more than 20 seconds, more preferably more than 60 seconds and most preferably more than 90 seconds.

An example of a nebuliser will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-section through the nebuliser showing the nozzle, reservoir of pressurised gas and reservoir of liquid;

Fig. 2 is a perspective view of a first nozzle;

Fig. 3 is a partial cross-sectional view with the gas inlet shown in perspective of the nozzle of Fig. 2; and

Figs. 4 to 6 are views similar to Fig. 3 showing alternative nozzle configurations.

The nebuliser consists of three basic components, namely reservoir of pressurised gas more commonly referred to as a cylinder 1 . The term "cylinder" should not be in any way considered limiting on the shape of the reservoir, it is simply the most common term used to apply to such a reservoir. Secondly, there is a liquid reservoir 2 and thirdly a nozzle 3. All three components are intended to be integrally connected together as a replaceable cartridge for a larger system. The components could be loaded by the user into a retaining unit, and upon a user input, such as the shutting of a lid on the retaining unit, connections between the components could be opened automatically such that gas is allowed to flow from the cylinder to the nozzle, and liquid is allowed to flow up into the nozzle, and subsequently the aerosol is generated. The aerosol would continue to be generated until either the reservoir of gas or the reservoir of liquid is emptied. After use, the components are removed for disposal or recycling. The cylinder 1 is a cylinder of compressed gas with an internal volume of 50ml and a pressure of 200 bar. The nozzle 3 consists of a frusto-conical reverse flow cyclone chamber 4 which can be injection moulded in one or more components. The chamber has a generally conic form with an end face 5 at the bottom of the cyclone chamber, a flared wall 6 leading to a round end face 7 at the opposite end. A liquid inlet 8 is provided in the bottom of the cyclone chamber 5, while a gas inlet 9 is shown tangential to the end face 7 and side wall. There may be more than one such inlet and this may be tangential, helical, or scrolled, in order to efficiently establish a swirling flow about the main axis X of the nozzle, in line with good cyclone design practise. The swirling of the gas generates a vortex causing a low pressure region towards the centre of the chamber 6. This draws liquid up from the liquid reservoir 2 via the liquid inlet 8. The high shear forces generated by the vortex break up the liquid such that an aerosolised plume of liquid and gas is emitted through the outlet 10. A vortex finder 1 1 surrounds the outlet 10 and projects axially a short way into the chamber 4 to prevent droplets exiting the cyclone chamber prior to being classified.

As can be seen in Fig. 3, the liquid inlet 8 is positioned in a small upwardly flared indent 13 in the bottom 5 of the chamber 2. This provides a conical vortex stabiliser at the base of the cyclone to minimise precession and help ensure that the low pressure cyclone core remains directly above the liquid inlet to provide negative driving pressure.

Typical dimensions for the nozzle are as follows, the gas inlet 9 has a cross-section of 0.199 mm 2 , taken perpendicular to the direction of flow at the narrowest point. The vortex finder 10 has an internal diameter of 595 μηι. The internal diameter of the chamber 4 adjacent to the end 7 is 1 .78 mm excluding any influence of the gas inlet 9. The internal angle of the vortex chamber 4 is 17° and the liquid inlet 8 has an internal diameter of 133 μηη and a length of 10mm.

As an example, a 50 ml compressed air cylinder at a pressure of 200 bar will in theory run for 3 minutes and 29 seconds at an operating gas pressure of 1.4 bar. This would establish a negative pressure of 0.5 bar at the liquid inlet 8 drawing 2.3 ml per minute with a 50% fine particle fraction. If the nebuliser was to be used for 2 minutes, and accounting for a 75% liquid loss between the outlet 10 and the mouth of the user (i.e. 75% of the liquid in the reservoir 2 is lost to the atmosphere and not inhaled) this would result in

approximately 1 .1 ml of liquid droplets in an aerosol at the mouth with half of this volume in droplets small enough to be inhaled (i.e. smaller than 5 μηη diameter).

Alternative positioning of the liquid inlet is shown in Figs. 4, 5 and 6. In all of these, a needle 15 is inserted through the apex 5 and into the chamber. The liquid inlet 8 is required to have a relatively small inner diameter and, as can be seen in Figs. 4 and 6, this is set by the internal bore of the needle 15 allowing the orifice in the injection moulded nozzle 3 to be larger.

In Fig. 4, the end 16 of the needle is flush with the wall of the chamber 2. In Fig. 5, it protrudes to a small extent into the chamber 4 while in Fig. 6 it protrudes to such an extent that it is inside the vortex finder 1 1. The provision of the needle allows the liquid outlet to be positioned in the position of optimal suction as generated by the swirling gas.