Apparatus and Method for Generating an Aerosol

Abstract

The present invention is directed to improvements related to the generation of aerosols and outlines an apparatus and methods which supports deagglomeration and counteracts reagglomeration of aerosol particles. The apparatus is provided with an arrangement of inlet conduits for pressurized gas that promote transportation with a rotational flow towards an exit conduit. In order to further support production of high quality aerosols, the apparatus can be provided with an impactor aligned with the exit conduit with at least one impacting surface that minimizes formation of impact residues.

Claims

1. An aerosol generating apparatus having a main axis of rotational symmetry and comprising: an at least partially spherical powder chamber for loading a powder therein and mixing the powder with pressurized gas, the powder chamber having one or several compartments; at least two inlet conduits connected to a pressure chamber and being operable to introduce the pressurized gas to the powder chamber by at least two inlet orifices of said at least two inlet conduits, respectively, and create a powder suspension in the pressurized gas in the powder chamber; and an ejection conduit, the ejection conduit having an inlet from the powder chamber and opening at an exit orifice to an ambient pressure, the ejection conduit opening at the exit orifice being operable to form an aerosol when the powder suspension in the pressurized gas is released from the exit orifice, wherein (i) each of the at least two inlet conduits has a symmetry axis extending into a respective projection line and the at least two inlet conduits are arranged to admit inlet flows in opposite directions; (ii) the inlet conduit projection lines are equidistant to an inlet conduit parallel plane which contains the apparatus main axis of rotational symmetry; (iii) the inlet conduit projection lines form acute angles with the apparatus main axis of rotational symmetry; and (iv) the at least two inlet conduits have inlet orifices located in a spherical part of the at least partially spherical part of the powder chamber and operable to form a rotating flow of the powder suspension in the pressurized gas.

2. The apparatus according to claim 1, wherein the powder chamber comprises a substantially hemispherical compartment, comprising the at least two inlet orifices for pressurized gas.

3. The apparatus according to claim 1, wherein the powder chamber is spherical and wherein a distance between said inlet orifices is equal or slightly less than the diameter.

4. The apparatus according to claim 1, wherein the powder chamber further comprises a substantially cylindrical compartment and a substantially ellipsoid compartment.

5. The apparatus according to claim 4, wherein the substantially ellipsoid compartment comprises the ejection conduit.

6. The apparatus according to claim 1, wherein a distance between each of the conduit projection lines and the inlet conduit parallel plane is from about 0.01 to about 1 mm.

7. The apparatus according to claim 1, wherein the ejection conduit has an abrupt inlet.

8. The apparatus according to claim 1, wherein the ejection conduit has a substantially uniform cross-section, substantially shaped as a cylinder.

9. The apparatus according to of claim 1, further comprising an impactor adapted to meet the aerosol powder discharged from the exit orifice.

10. The apparatus according to claim 9, wherein the impactor comprises an impactor body having an impacting surface and, between the impactor body and an impactor housing, an impactor channel is provided with a substantially ring-shaped shaped cross-section.

11. The apparatus according to claim 1, wherein the at least two inlet conduits are each substantially cylindrical, and the at least two inlet orifices are each an ellipsoid.

12. The apparatus according to claim 10, wherein the impactor body comprises a substantially cylindrical part and a conical part and wherein said conical part provides a primary impacting surface.

13. The apparatus according to claim 12, wherein the impactor further comprises a secondary impacting surface provided at a cylindrical inner surface of a cylindrical part of the impactor housing at an entrance of the impactor channel.

14. The apparatus according to claim 12, wherein the conical part is a recessed cone comprising a surface with a tangent having an angle with the main axis of rotational symmetry increasing with a cone radius, admitting substantially the same acute impact angle for each powder agglomerate meeting the impacting surface.

15. The apparatus according to any claim 1, comprising at least one additional inlet conduit with a projection line that intersects the inlet conduit parallel plane.

16. A method of generating an aerosol comprising the steps of: a) loading an at least partially spherical powder chamber with an aerosolizable powder, the powder chamber having a main axis of rotational symmetry and one or several compartments; b) releasing a pressurized gas and introducing it into the powder chamber by at least two inlet conduits entering by at least two inlet orifices of said at least two inlet conduits, respectively, in a spherical part of the at least partially spherical powder chamber and providing a suspension of mixed gas and powder, wherein (i) each of the at least two inlet conduits has a symmetry axis extending into a respective projection line and the at least two inlet conduits are arranged to admit inlet flows in opposite directions; (ii) the inlet conduit projection lines are equidistant to an inlet conduit parallel plane which contains the powder chamber main axis of rotational symmetry; and (iii) the inlet conduit projection lines form acute angles with the powder chamber main axis of rotational symmetry; c) establishing a rotating flow of the suspension in at least one compartment of said powder chamber; d) admitting a flow of the suspension along the powder chamber inner walls to an ejection conduit of the powder chamber, the ejection conduit having an inlet from the powder chamber and opening at an exit orifice to an ambient pressure; e) releasing the suspension through the exit orifice to form an aerosol, subjecting the aerosol to at least one impacting surface, and transporting the aerosol through a substantially ring-shaped impactor channel; and f) optionally collecting the so formed aerosol.

17. The method according to claim 16, wherein the pressurized gas has a pressure of at least 50 bar.

18. The method according to claim 16, wherein the rotating flow is established in a substantially hemispherical compartment of the powder chamber.

19. The method according to claim 16, wherein the at least one impacting surface comprises a primary impacting surface provided on a conical part of an impactor body, wherein the conical part is a recessed cone comprising a surface with a tangent having an angle with the powder chamber main axis of rotational symmetry increasing with a cone radius, such that the aerosol particles meet the primary impacting surface at substantially the same acute impact angle .

20. The method according to claim 19, wherein the aerosol particles subsequent to the primary impacting surface meet a secondary impacting surface provided at a cylindrical inner surface of a cylindrical part of an impactor housing at an entrance of the impactor channel at a substantially non-perpendicular angle.

Description

SHORT DESCRIPTION OF DRAWINGS

[0024] FIG. 1 shows an aerosol generator according to the invention through a section representing a plane of symmetry with the inlet orifices for pressurized gas schematically shown.

[0025] FIG. 2 shows the aerosol generator with the inlet orifices as viewed through plane A-A in FIG. 1. Also indicated are the inlet conduit parallel plane B-B and its normal plane C-C.

[0026] FIG. 3 shows a section of the apparatus, wherein the inlet conduit parallel plane B-B is the plane of the paper demonstrating how a schematically shown inlet conduit projection line (shown in FIG. 2) has an angle to the normal plane C-C.

[0027] FIG. 4 shows the impactor and is housing in an enlargement of the arrangement of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat.

[0029] It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof. If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those skilled in the art to which this invention pertains.

[0030] It must be noted that, as used in this specification and the appended claims, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise.

[0031] The term about as used in connection with a numerical value throughout the description and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. Said interval is 10%.

[0032] Other features and uses of the invention and their associated advantages will be evident to a person skilled in the art upon reading the description and the examples.

[0033] It is to be understood that this invention is not limited to the particular embodiments shown here. The following examples are provided for illustrative purposes and are not intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof.

[0034] The following definitions include terms used in the detailed description of the invention, but are also valid for the same terms in any earlier general description of the invention and the appended claims. Certain terms are also defined in the general, earlier contexts of the description.

[0035] A powder chamber is the chamber set to accommodate the powder to be aerosolized. The powder camber be essentially spherical or have other symmetrical shapes.

[0036] An inlet conduit is a conduit for transporting pressurized gas to the powder chamber and may include one or more releasable valves to be released when charging the apparatus. The inlet conduit or conduits terminate with an inlet orifice to the powder chamber.

[0037] An ejection conduit is an exit conduit of the powder chamber for discharging the mixture of powder and pressurized air from the powder chamber. The ejection conduit terminates with an ejection orifice to ambient air.

[0038] The main axis of rotational symmetry of the apparatus is the axis of symmetry the apparatus through the exit nozzle of the apparatus. An infinite number of symmetry planes can be defined to be aligned with and containing the rotational axis of symmetry and intersecting each other at arbitrary angles.

[0039] An inlet conduit projection line coincides with the axial symmetry line of the essentially cylindrical inlet conduit extends from inlet orifice into the powder chamber. Inlet conduit projection lines of the at least two inlet orifices are equidistant to a plane which contains the main axis of rotational symmetry of the apparatus termed inlet conduit parallel plane. Off-set distance is the distance between the inlet conduit projection lines and the inlet conduit parallel plane. The off-set distance is >0. The projection lines of at least two inlet orifices for pressurized gas are off-set from the main axis of rotational symmetry. Accordingly, the projection lines of further, additional inlet orifices may lie within one single plane of symmetry and intersect the projection line through the exit orifice.

[0040] An acute angle is an angle less than about 70 degrees, preferable less than 60 degrees. An acute angle is formed between the inlet conduit projection lines and the main axis of rotational symmetry of the apparatus.

[0041] An impact angle is the angle between the path of aerosol particle or an agglomerate of aerosol particle travelling from the ejection orifice and onto the impactor surface.

[0042] FIG. 1 shows the apparatus 10 in a section according to a symmetry plane with a main axis of rotational symmetry 28. The powder chamber 12 has a hemispherical part 12B, a cylindrical part 12B and an ellipsoidal part 12C. The apparatus can be accommodated in housing or a similar arrangement. In FIG. 1 the two inlet conduits 18A and 18B and their orifices are only schematically shown and it is referred to FIG. 2 that is a view from above from section A-A in FIG. 1 for their arrangements. FIG. 1 further schematically shows the ejection conduit 20 with its ejection orifice and the impactor arrangement 30. The impactor arrangement 30 comprises an impactor body 32, a ring shaped impactor channel 36 providing an annular slit surrounding the impactor body 32. The impactor body 32 is provided with a cylindrical part and a conical part that will be described in more detail in the context of FIG. 4. FIG. 1 further illustrates the rotating flow established by the pressurized gas from the inlet conduits and how a flow is established forwards along the powder chamber inner walls towards the ejection conduit.

[0043] The view from above along section A-A in FIG. 1 is shown in FIG. 2 and demonstrates two oppositely arranged inlet conduits with inlet orifices to the powder chamber. FIG. 2 further shows inlet conduit projection lines 18A and 18B, respectively which have the same distance to the inlet conduit parallel plane B-B. This distance is between 0.01 to 1 mm. The inlet conduit parallel plane B-B has a normal plane C-C termed inlet conduit normal plane. The inlet conduits are cylindrically arranged and the inlet orifices are ellipsoidal with a largest dimension of in the range of about 0.5 to 1 mm. The exit orifice has a diameter in the range about 0.2 to 1 mm, in a powder chamber volume of about 1 ml. FIG. 2 also demonstrates the opposite direction of the inlet flows of pressurized gas.

[0044] FIG. 3 further illustrates the angular arrangement of the inlet conduits, In FIG. 3 one inlet conduit projection line from inlet conduit 18B is depicted to form the acute angle with the inlet conduit normal plane (C-C in FIG. 2) that has a value in the range of 35-65 degrees. The other inlet orifice can be depicted in the same manner with an acute angle . These angles can have the same or different acute values.

[0045] FIG. 4 is a detailed view of the impactor 30 in FIG. 1, showing the impactor accommodated in the impactor housing. The annular slit 36 surrounding the impactor body 32 has width of about of about 0.1 to 0.2 mm and the cylindrical part of the impactor body has diameter of 3-4 mm. The annular slit length is 2-3 mm. FIG. 4 further demonstrates the recessed cone of the impactor body with its curved primary impacting surface 34. It is schematically shown how agglomerates travel from the ejection conduit of the powder chamber and that the curvature of the impacting surface admits that a substantially constant acute impacting angle is maintained irrespectively of where the impacting surface is hit. It is also schematically shown how the tangent to the surface has an angle with the main axis of symmetry that increases with the cone radius of the recessed cone. The so arranged primary impacting surface 34 will counteract formation of impact residues which may form when agglomerates hit the primary impacting surface 34 perpendicularly or close thereto. The impactor housing 38 is dimensioned to counteract pile up of aerosolized material and is formed to admit the annular slit 36 to extend between the cylindrical part of the impactor body and to provide an inner surface of the cylindrical part of the impactor housing 38. A secondary impacting surface 40 is formed at the inner surface of the cylindrical part of the impactor housing in region of the entrance of the annular slit. In operation, powder (aerosol particles) will depart essentially tangentially from the primary impacting surface and hit the secondary impacting surface at an essentially non-perpendicular impacting angle. The aerosol flow rate will retard in the annular slit and the aerosol will be distributed form the impactor orifice as a well-defined aerosol plume. The described impactor with its complementary impacting surfaces provides a very efficient way of producing homogenous and well-defined aerosols arriving in a plume shape from the slit. It has been found that powders that have been regarded as difficult to handle by forming needle shaped crystals efficiently can be broken up by the apparatus according to the invention.