MIXING CHAMBER FOR MIXING TOGETHER A GASEOUS AND A LIQUID CONSTITUENT

Abstract: A mixing chamber (1) is described for mixing together a pressurised gaseous and liquid constituent, which chamber is provided with separate feed connections for the constituents. At least one of the feed connections is formed by narrow passages in the wall of the mixing chamber in the form of a porous part (4). The mixing chamber (1) can be made up of several parts (2, 3) with the porous part (4) fixed between them, or it can be integral therewith, for example by being made from a porous material itself. An aerosol comprising a mixing chamber (1) of the type described above is also described.

Description: Mixing chamber for mixing together a gaseous and a liquid constituent. The present invention relates to a mixing chamber for mixing together a pressurised gaseous and liquid constituent, which mixing chamber is provided with separate feed connections for the pressurised constit- uents of the mixture to be formed, and with a discharge connection for the mixture formed to a chamber with lower pressure, at least one of the feed connections being formed by narrow passages in the wall of the mixing chamber. The mixing together of a gas and a liquid with a view to forming a fine mist can lead to difficulties if the fine droplets formed in a spray nozzle merge into larger droplets in the jet. This leads to an irregular distribution of the liquid on a sprayed surface. If a propellant which dissolves in the liquid and evaporates easily again from it is used, this merging can be avoided, but there is an increasing objection to the use of such propellants on account of their harmful effects on the environment, or on account of their combustibi- lity. If air is used as the propellant, mixing it well with the liquid by turbulence in a mixing chamber can actually prevent the droplets formed from merging, but it is difficult to obtain a good mix in the case of small mixing chambers. This applies in particular in the case of aerosols in which the mixing chamber with the dispens¬ ing valve and the spray nozzle has to be combined to a small unit for placing on an aerosol. This stands in the way of a more widespread use of aerosols working with air as the propellant, so that the aerosols with harmful propellants still remain in general use. A likely ban on the latter aerosols in the future is part of the reason why there is a great need for a solution to this problem. Besides, this mixing problem is not limited to aerosols, and finding a solution for such aerosols can lead to applications in other fields. One solution is described in NL-A-89 01877 of Applicant, which describes a mixing chamber made up of two parts which have surfaces touching each other and abutting the inside wall of the mixing chamber. The narrow passages are in this case formed by grooves in at least one of the abutting surfaces which together with the other surface bound the narrow passages. The present invention provides another simple solution to the provision of narrow passages in the wall of the mixing chamber, and to that end is characterised in that the narrow passages are formed by at least one porous part present locally in the wall of the mixing chamber. It has in fact been found that through the use of such a porous part with narrow passages a mixing suitable for the abovementioned purpose can be obtained, in which the dimensions of the passages can depend on the viscos- ity of the liquid and the dimensions and layout of the assembly of mixing chamber and discharge means connected to it. Further embodiments of the invention are described in claims 2 - 6. The invention also relates to an aerosol intended for atomising a liquid by means of a propellant, in particular air, which aerosol contains a mixing chamber according to the invention. The invention will be explained in greater detail below with reference to the appended drawing, in which: Fig. 1 shows a schematic section of an example of an embodiment of a mixing chamber according to the invention; Fig. 2 shows a schematic section of another example of an embodiment of a mixing chamber according to the invention. The mixing chambers shown in Figs. 1 and 2 form a part of an aerosol not shown in any further detail. The mixing chamber 1 in Figure 1 comprises a beaker-shaped bottom part 2 and an annular top piece 3, separated by an annular porous part 4, which can be, for example, a porous plastic, a sintered material, or a porous ceramic material. Apart from materials with a relatively random pore distribution, materials which are provided in a very accurate way with narrow passages are also suitable. An example which can be mentioned in this connection is plastic which is provided with narrow passages using a laser, which passages have a very accurately determined orientation and size. It will be clear that the position and dimensions of the porous part 4 depend on the use, and can be altered if desired. The porous part 4 can comprise, for example, several smaller porous parts distributed over the periphery of the mixing chamber 1. The beaker 2 is provided at the bottom side with a connecting spout 5 for an immersion tube 6 which is immersed in the liquid present in the aerosol. The top edge 7 of the top piece 3 is in sealing contact with a sealing ring 8, which forms part of the release valve assembly of the aerosol. The bottom end of a hollow stem 10, which is connected to the spray head of the aerosol, projects into a central opening 9 of this ring 8. The bottom side of this stem 10 is connected to a pressure element 11, which is pressed upwards by means of a spring 12 resting against the bottom of the beaker 2, while the top position is bounded by a stop, which is not shown. In the case shown, the longitudinal bore 13 of the stem 10 is connected at two sides to the outside by means of a transverse bore 14, which in the situation shown lies above the sealing ring 8. The number of transverse bore openings can also be greater or smaller. On pressing in the stem 10, it slides into the opening 9, and the transverse bore 14 comes to lie at the other side of the ring 8, so that the longitudinal bore 13 then becomes connected to the inside of the mixing chamber. After pressing in the stem 10, the pressure of the propellant will cause the liquid to be expelled from the aerosol through the tube 6 into the annular space around the element 11 of the mixing chamber 1, while the propellant also enters said space through the pores or narrow passages of the porous part 4. An turbulence then occurs, with the result that a good mixing of liquid and propellant is obtained, which will lead to a fine mist when the mixture emerges from the spray nozzle of the aerosol. This is important particularly if air is used as the propellant, since air dissolves so little in the liquid to be atomised that the merging of droplets is not prevented. This can be avoided by mixing in air in the mixing chamber. In fact, this also applies to other propellants in which a mist formation without mixing in is inadequate. The pores of the porous part 4 must have such a flow cross-section that good mixing takes place. This also depends, of course, on the shape of the mixing chamber 1 and on the type of liquid to be atomised_ With a suitable selection of the flow cross- section of the pores or passages of the porous part 4 in relation to the size of the immersion tube 6 and/or the annular porous part 4 itself, an aerosol provided with such a mixing chamber is also found to work satisfactor¬ ily if it is held upside down and the pores or passages of the porous part 4 are thus connected to the liquid space and the tube 6 to the propellant chamber. Figure 2 shows a different embodiment of the mixing chamber according to the invention, in which the annular top piece 3 is provided with a collar 15, which fits on the top edge 16 of the beaker 2, while the internal diameter of the collar 15 corresponds to the external diameter of the top edge 16, and the internal diameter of the part of the top piece 3 abutting the collar 15 is equal to the internal diameter of at least top edge 16 of the tub 2. The porous part 4 in this case is situated between the top edge 16 of the tub 2 and a shoulder 17 of the top piece 3. In order to ensure that the interior of the mixing chamber 1 can be connected by means of the porous part 4 to the outside of the mixing chamber where the propellant is situated, the outside wall of the top edge 18 of the beaker-shaped part 2 is provided with grooves 19 which with the collar 15 bound passages 20. It will be clear that the grooves 19 can also be formed in the collar 15. It will be clear that the invention is not limited to the examples of embodiments described. For example, the wall of parts 2 or 3 can also be porous itself. A special embodiment in this respect is a mixing chamber which is integral with the porous part. This means that the mixing chamber comprises one unit and is locally porous. The mixing chamber can thus be made of, for example, plastic or the like, and can be provided locally with narrow passages. The mixing chamber could also be made entirely of a porous material. Finally, it is pointed out that the invention can be used anywhere similar problems occur.

Claims: Claims 1. Mixing chamber for mixing together a pressurised gaseous and liquid constituent which mixing chamber is provided with separate feed connections for the pressurised constituents of the mixture to be formed, and with a discharge connection for the mixture formed to a chamber with lower pressure, at least one of the feed connections being formed by narrow passages in the wall of the mixing chamber, characterised in that the narrow passages are formed by a porous part (4) present locally in the wall of the mixing chamber (1) . 2. Mixing chamber according to claim 1, characterised in that the porous part (4) is made of a material which is selected from: a sintered material, a porous plastic, or a porous ceramic material. 3. Mixing chamber according to claim 1, characterised in that the mixing chamber (1) comprises two parts (2, 3) which are separated by the porous part (4). 4. Mixing chamber according to claim 3, characterised in that one part (2) of the mixing chamber is made beaker-shaped and is provided with a connection for one constituent, while the other part (3) is a top piece (3) fitting on the opening of said beaker-shaped part (2) , while the porous part (4) is located between the end face of the top piece (3) and the end face (16) of the beaker-shaped part (2) and is connected on the outside with a feed for the other constituent. 5. Mixing chamber according to claim 4, characterised in that the top piece (3) or the beaker- shaped part (2) comprises a collar (15) fitting around the outside wall of the beaker-shaped part (2) or the top piece (3) , and in that the outer wall or the collar (15) is provided with grooves (18) which together with the collar (15) or the outer wall bound the feed (19) for the other constituent. 6. Mixing chamber according to claim l or 2, characterised in that the mixing chamber (1) is integral with the porous part (4) . 7. Mixing chamber according to one of claims 1 - 6, intended for an aerosol for atomising a liquid by means of a propellant above the liquid, and in particular air under pressure, which propellant must be mixed with the liquid to be atomised, while the mixing chamber discharge device is formed by the hollow stem of a spray head, of which the bore can be connected by means of a release valve to the mixing chamber, characterised in that the porous part (4) is normally connected to the propellant chamber of the aerosol. 8. Aerosol intended for atomising a liquid by means of a propellant, in particular air, which aerosol com- prises a mixing chamber according to one or more of the preceding claims.

Inventors: VAN DER HEIJDEN EDGAR IVO MARI, VAN DER HEIJDEN, EDGAR, IVO, MARIA
Applicants: AIRSPRAY INT BV, AIRSPRAY INTERNATIONAL B.V.
Application year: 1992
Main classification: B65D83
IPC codes: B65D83