WO2013050734A1

WO2013050734A1 - An improved portable apparatus for generating and broadcasting an aerosol mist

Info

Publication number: WO2013050734A1
Application number: PCT/GB2012/051989
Authority: WO
Inventors: Ian Singleton; David Thomas TAYLOR
Original assignee: Amazon Bioguard Limited
Priority date: 2011-10-03
Filing date: 2012-08-15
Publication date: 2013-04-11
Also published as: GB201110906D0; GB2492424A; GB201117119D0

Abstract

A substantially closed rectangular chamber (1) equipped with a constant liquid level control device (19) has a cylindrical tube (2), open at one end (front) and closed at the other by a fan (5), mounted horizon¬ tally along-side an upper edge of the chamber. A piezoelectric transducer (10) located in the front quarter of the chamber base furthest from the cylinder generates an aerosol and a curtain (15) dropped from the top of the chamber by about a quarter its height restricts its movement, directly above the piezoelectric transducer. The chamber and cylinder are made contiguous by two conduits the first (3) of which leaves the chamber, at a right angle to its wall, above the liquid level and enters the cylindrical tube from below. The second conduit (4) is straight passes from the back of the upper chamber to penetrate the cylindrical tube at an acute angle to the cylinder and above a horizontal plane.

Description

AN IMPROVED PORTABLE APPARATUS FOR GENERATING AND

BROADCASTING AN AEROSOL MIST

AREA OF INVENTION

The present invention is directed toward the efficient formation and harvesting of an aerosol from a liquid and air with dispersed phase particles in the size range 1 to 15 microns in diameter and broadcasting it into a large volume from a self contained and portable device.

BACKGROUND

It is well known to generate aerosols by the application of pressure waves to a liquid phase in order to, for example, prepare therapeutic agents for inhalation, generate visual effects or affect broadcast distribution of non-volatile liquids into large volumes. Devices to achieve these effects are variously known as nebulisers, atomizers or misters and generate the pressure waves by water flow, rotating discs, gas-flow (EP 070715, EP0627266, FR2684005, GB1431081) or piezoelectric transduction (GB1069048). In this specification we shall refer to the process of aerosol formation as nebulisation.

In the context of portability and self containment i.e. not dependant on an external source of pressure, devices based on piezoelectric transducers possess many advantages. However, there are also drawbacks:

a) Limitation on the volume of liquid that may be converted to an aerosol and dispersed by the need to maintain a constant height of liquid above the piezoelectric transducer;

b) Limitation to the distance travelled by the presence of too high a proportion of oversized liquid phase particles which agglomerate and coalesce with normal size particles causing premature sedimentation of the liquid phase;

c) Limitation to the distribution of the liquid phase particles by a reduction in particle count due to the high particle density at the point of formation enhancing agglomeration and coalescence, and;

d) Liquid phase formed from liquid phase particles wetting surfaces within the apparatus to cause leakage of liquid phase from the apparatus

As we will show later, the present invention overcomes the above mentioned limitations by forming the aerosol in an integrated generation chamber and delivery system designed to co-optimise the volume of bulk liquid converted to an aerosol and the efficient delivery (broadcasting) of the 5-15 micron particle diameter component of the generated aerosol particle size distribution (the "dry" mist) from the generation chamber into a large volume (e.g. a room) within which the invention is placed.

Following extensive research we identified a series of design features to overcome these drawbacks by:

1) controlling the input of the liquid phase into the aerosol generation chamber to preserve a constant level of liquid phase in the chamber during the aerosol formation process;

2) screening out the larger liquid phase "aerosol" particles to minimise particle coalescence;

3) arranging that the pathway used to extract the aerosol from the generation chamber is as straight as possible and that free liquid phase formed by particles that collide with and wet the inner surface of the pathway drains back into the generation chamber, and;

4) rapid dilution of the aerosol after harvesting to reduce particle-particle collision rate and consequent increase in particle size distribution.

TESTING OF DIFFERENT AEROSOL CHAMBER DESIGN FEATURES

Experiments were carried out to determine the effect of various modifications to the design and operation of the Aerosol Generating Chamber and its associated extraction mechanism at room temperature. The prototypes demonstrating the configuration and operational changes shown in table 1 were mocked-up and each run for 20 minutes with the same liquid using the same initial level recommended by the piezoelectric transducer manufacturer (WHC-1730/20-48V from Beijing Dongfang Jinrong Ultrasonic Electric Company Ltd). The efficiency with which the liquid was formed into an aerosol, emitted from the apparatus and how wet it felt (any drips from apparatus) was judged by visual and tactile observation of the aerosol mist expelled and the liquid lost from the Aerosol Generating Chamber. The results are shown in table 1. TABLE 1

Effect of configuration changes to an Aerosol Generator on its Performance.

Table 1 indicates that each of the design changes made had a significant effect on performance and cumulatively the effects produced a step change in the efficiency of converting a liquid into an aerosol and broadcasting that aerosol into a closed space. SUMMARY OF THE INVENTION

The invention is achieved by generating the aerosol in a chamber (Aerosol Generation Chamber) designed to maintain a constant height of the liquid phase to be nebulised above a piezoelectric transducer, by way of a closed circuit liquid by-pass conduit containing a liquid height detector controlling a reversible pump connecting the chamber to a separate liquid phase stock container. A piezoelectric transducer is incorporated into the base of the aerosol generation chamber, off-set from the chamber centre and set to vibrate within the frequency range 0.5 to 1.85 M. Hz, preferably at the higher end of this range (1.25 to 1.85 M. Hz ), at a power loading of about 30 Watt.

The top of the Aerosol Generation Chamber is contiguous with a conduit to harvest the generated aerosol (Aerosol Harvesting Conduit) and an Air Inlet Conduit to create a positive pressure in the generation chamber. On leaving the generation chamber both these conduits penetrate into a cylindrical Dilution and Delivery Tube running horizontally alongside the top of the Aerosol Generation Chamber, closed with a fan at one end and open at the other end: the purpose of the fan being to create an air flow along the Dilution and Delivery Tube towards the open end.

This air-flow serves a number of purposes:

a) it creates a positive pressure in the Aerosol Generating Chamber via the Air Inlet Conduit;

b) it sucks the generated aerosol out of the Aerosol Generating Chamber via the Aerosol Harvesting Conduit, and;

c) it dilutes the aerosol in the Dilution and Delivery Tube and enhances broadcasting of the diluted aerosol from the apparatus.

The Aerosol Harvesting Conduit is a straight tube, open at both ends which are cut at right angles to its wall, and connects the top of the Aerosol Generation Chamber to the Dilution and Delivery Tube, entering the side of the latter at an angle of about 19 degrees to it's wall and 12 degrees above the horizontal plane, in the direction of the air-flow.

The Air Inlet Conduit passes through the side of the Aerosol Generation Chamber above the level of the liquid phase when the apparatus is in operation and bends through 90 degrees to enter the Dilution and Delivery Tube from underneath at a location between the fan and the Aerosol Harvesting Conduit entrance. The end of the Air Inlet Conduit within the Aerosol Generating Chamber is open and may be flush with the chamber wall while the end within the Dilution and Delivery Tube is blanked off with a "letterbox" slot cut into the conduit wall facing the fan and preferably adjustable in size.

The Aerosol Generating Chamber may be cylindrical or preferably rectangular in shape. In either case the important principles being exploited in this invention are that: a) the piezoelectric transducer is located in the base of the chamber and displaced laterally as far as practical from being directly underneath the open end of the Aerosol Harvesting Conduit, and;

b) the entry to the Aerosol Harvesting Conduit is protected from being accessed by the larger liquid particles thrown up with the aerosol by the piezoelectric transducer by a curtain suspended from the top of the chamber.

We believe that by controlling:

a) the height of liquid in the Aerosol Generation Chamber to maintain the focus of the piezoelectric transducer at the air-liquid interface;

b) the configuration of the Aerosol Harvesting Conduit relative to its surrounding curtain and the position of the piezoelectric transducer in the base; c) a positive pressure in the Aerosol Generation Chamber;

d) an extraction enhancing air flow through the Dilution and Delivery Tube, and;

e) the angle of entry of the, straight Aerosol Harvesting Conduit into the Dilution and Delivery Tube at as shallow an angle from the horizontal as possible, that all the aforementioned difficulties with previous attempts to build a portable apparatus for generating and broadcasting a small particle size aerosol mist have been overcome.

DESCRIPTION OF THE INVENTION

The Invention will now be described in detail with the aid of drawings 1 to Si- Drawing 1 is a schematised top view of the inventive apparatus set out for clarity rather than representing any particular configuration of the assembly. It shows an axis (A— B) through which a cross-sections are taken in drawing 2 & 3. Drawing 2 shows a cross-section through the Aerosol Generating Chamber along a plane through the axis A— B shown in drawing 1 viewed from the front of the apparatus.

Drawing 3 shows a cross section through the same plane of the Aerosol Generating Chamber as shown in drawing 2 but viewed from the back of the apparatus.

DRAWING 1

Drawing 1 is a schematised top view of the inventive apparatus set out for clarity rather than representing any particular configuration of the assembly. It also shows the axis (A — B) through which the cross-sections shown as drawing 2 and 3 are drawn.

A rectangular Aerosol Generating Chamber (1) with a volume of from 750 to 1250 cubic centimetres preferably 1050 cubic centimetres, fabricated from any suitable materials including metals, plastics and polymers, has a cylindrical Dilution and Delivery Tube (2), fabricated from similar materials, measuring from 150 mm to 230 mm preferably 170 mm in length with a diameter in the range 50 mm to 100 mm preferably 70 mm mounted alongside a top edge. The Dilution and Delivery Tube (2) is open at one end (front of apparatus) and closed by a fan (5) at the other end (rear of apparatus) which is used to create an air-flow along the Dilution and Delivery Tube (2) toward its open end. It is mounted along the top edge of one side of the Aerosol Generating Chamber (1).

The top of the Aerosol Generating Chamber (1) and the Dilution and Dispersion Tube (2) are connected by two conduits. The first is an Aerosol Harvesting Conduit (3) which is a straight cylindrical tube having a diameter of from 18 mm to 25 mm preferably 22 mm and a length of from 90 mm to 110 mm preferably 100 mm with both ends cut at right angles to its wall. It is located between the top-rear of the Aerosol Generating Chamber (1) and slopes down toward the back of the chamber by from 10 degrees to 14 degrees preferably 12 degrees from the horizontal. It passing through the chamber wall and entering the Dilution and Delivery Tube (3) at an angle of from 17 to 21 degrees preferably 19 degrees to its wall.

The second connection between the upper part of the Aerosol Generating Chamber (1) and the Dilution and Delivery Tube (2) is the Air Inlet Conduit (4) which is approximately the same diameter as the Aerosol Harvesting Conduit (3) and is open ended where it passes through the wall of the Aerosol Generating Chamber (1) at a height above the level that liquid will occupy when the apparatus is in normal use. Once out of the chamber the conduit bends through ninety degrees and enters the Dilution and Distribution Tube (2) through its base between the Aerosol Harvesting Conduit (2) and the fan (5). The end of the Air Inlet Conduit within the Dilution and Delivery Tube is blanked off and a "letterbox" slot is cut into the wall, adjustable in size to control the pressure build up in the Aerosol Generating Chamber (1) and facing the fan,

The piezoelectric transducer (10) may be a commercially available ultrasonic transducer vibrating in the frequency range 0.5 to 1.75 MHz preferably 1.25 to 1.75 MHz with a power loading of 30 Watt, and is set in the base of the Aerosol Generation Chamber (1) in the front quarter furthest away from the Dilution and Delivery Tube (2) of the Chamber.

Drawing 1 also shows schematically other necessary components known in the art such as a reversible pump (6) which takes the liquid to be aerosolised from the stock supply container (7) to the Aerosol Generating Chamber, through the portal (17), at the beginning of a use, pumps it back at the end and maintains a constant height of liquid in the chamber during use using the by-pass conduit (18) and liquid level controller device (19). The apparatus is powered by electricity (9) which can optionally support Direct or Alternating current and optional features such as thermostatic heaters. The apparatus is operationally controlled by an application specific printed circuit board (8).

DRAWING 2

Drawing 2 shows a cross-section through the Aerosol Generating Chamber and Dilution and Delivery Tube assembly along a plane through the axis A— B shown in drawing 1 viewed from the front of the apparatus.

Whilst we do not wish to be bound by theory our experiments have indicated that the aerosol generating performance of the apparatus is critically dependent on the relative positions of the Aerosol Harvesting Conduit (3), the curtain (15) protecting it from the larger (i.e. those unable to resist gravitational forces) aerosol particles thrown up by the piezoelectric transducer (10) and the exact location of the piezoelectric transducer in the base of the Aerosol Generating Chamber. Drawing 2 shows the optimum configuration of these components in the Aerosol Generating Chamber with the inlet to the Aerosol Harvesting Conduit (3) being as far away from the piezoelectric transducer as is practically possible and either an L shaped or diagonal curtain, the latter not shown in drawing 2, dependant on the properties of the liquid to be aerosolised, hanging down from the top of the chamber by from 35 mm to 70 mm preferably 50 mm effectively Shielding the quarter of the upper region of the Aerosol Generating Chamber (1) directly above the piezoelectric transducer from the rest of the upper Chamber.

The Aerosol Generating Chamber (1) is sealed apart from the Aerosol Harvesting Conduit (3), by which the formed aerosol is harvested from the chamber, an Air Inlet Conduit (4), to allow air to enter the chamber and maintain a positive pressure within it and a bleed from the top of the bypass conduit used for liquid height control (18). The detailed structure and route by which the Aerosol Harvesting Conduit (3) and the Air Inlet Conduit (4) connect the Aerosol Generating Chamber (1) to the dilution and delivery Tube (2) has been discussed under Drawing 1.

The By-pass Conduit (18) takes the form of a glass or polymer tube having an inside diameter in the range from 2 mm to 6 mm preferably 4 mm which may be optically opaque or optically clear depending on the type of level control device (19), it is clearly essential to use optically clear materials and preferably minimise any light falling on the area if the level control device is of the optical type. The By-pass conduit (18) is held alongside the wall of the Chamber by any suitable means and narrows down to an air bleed at the top of the wall. The level control device (19) may be any such device commercially available but preferably an optical device and uses the level of liquid in the By-pass Conduit to control the level of liquid in the Aerosol Generating Chamber (1) by way of the reversible pump (6). The controlled level for the liquid in the Chamber will vary according to the properties of the piezoelectric transducer in use but will usually fall within the range 25 mm to 40 mm above the piezoelectric transducer. Drawing 2 indicates an appropriate level on the scale of the drawing.

Drawing 2 also shows a suitable support (21) for the chamber to ensure that the surface of the liquid in the Aerosol Generating Chamber (1) is horizontal: A plurality of supports may be used.

DRAWING 3 Drawing 3 shows a cross-section through the Aerosol Generating Chamber and Dilution and Delivery Tube assembly along a plane through the axis A— B shown in drawing 1 looking toward the front the front of the apparatus. It shows the Aerosol Harvesting Conduit (3) penetrating into the Dilution and Delivery tube (2), the position of the piezoelectric transducer and the curtain hanging down from the top of the chamber. Drawing 2 also shows the portal (17) through which the level of liquid in the Aerosol Generating Chamber (1) is controlled.

Operation of the Invention

In a first embodiment of the invention it is used to disinfect a closed space such as a room by distributing an aerosol of disinfectant into the room. The liquid disinfection medium is housed in the stock liquid container (7) and an appropriate sequence of events (programme) is selected for implementation by the printed circuit board (8). For example, once the selected programme is initiated:-

(a) The reversible pump (6) fills the aerosol generation chamber (1) to the specified (and subsequently controlled) level from the stock liquid container (7).

(b) The piezoelectric transducer (10) is initiated.

(c) The discharge fan (5) is initiated after a preset dwell time.

(d) Liquid phase consumed is replaced via the reversible pump under control of the liquid level indicator/controller (19).

(e) Following completion of the programmed time cycle the piezoelectric transducer (10) is switched off.

(f) The pump is reversed to drain residual liquid from the Aerosol Generating Chamber (1) to the stock liquid container (7).

(g) The discharge fan continues for a short time and then switches off to close the programme.

It will be clear to the reader that there are as many embodiments of this invention as there are non-therapeutic uses of liquid aerosols in the size range 1 to 15 microns in diameter. These would include disinfection and deodorising and perfumery of residential units, cruise liners, aircraft, places of entertainment, hotels, freight carriers and areas where hygienic conditions are critical and difficult to maintain, etc., and where the speed of delivery, the unattended nature of the operation and consequent much reduced labour costs are an advantage. Efficient aerosol generation depends on the focus of the piezoelectric transducer being on the air- water interface. This is affected by adjusting the controlled level of liquid in the Aerosol Generation Chamber (1) and will differ for liquids with different properties such as surface tension and viscosity both of which are effected by temperature which may be optionally controlled.

It should be noted that piezoelectric transducers generate considerable heat energy whilst working. To avoid overheating during prolonged running the transducer is optionally housed in an air cooled compartment with heat sinks including Peltier electric cooler technology available to prevent hot spots. Another option is to programme the transducer to turn itself off for a cooling down period once it has reached a set, high, temperature.

The heat energy generated by the transducer can transfer to the liquid being aerosolised which can improve Rate of aerosol production. A thermostatically controlled heater may be optionally incorporated into the Aerosol Generating Chamber to enhance aerosol production during the early stages of the process.

In further embodiments the apparatus may be programmed with a wide range of treatment times which can be selected for activation depending on the severity of the hygiene or perfumery challenge being undertaken and the properties of the liquid being aerosolised.

In yet a further embodiment of the invention wireless communication may be incorporated between the apparatus and a remote warning device which may provide warning signals that an area should not be entered until a safe period after a treatment had expired.

The apparatus may be fabricated from any suitable material bearing in mind the properties of the liquid to be aerosolised. Materials of construction for the Aerosol Generating Chamber and other components that come into contact with the liquid might include stainless steel, high density polyethylene, nylon, epoxy resins and polyacrylate and ABS plastics.

A further embodiment the invention may be provided with a radio-wave communication facility to enable multiple units to co-ordinate their programmes and allow them to be controlled from a central remote control unit.

Claims

WHAT WE CLAIM IS:-

Claim 1.

What we claim is a Cuboid aerosol generating chamber containing:

1) An electrical means of generating vibrational energy embedded in the base;

2) an area of the upper region of the chamber, above the means of generating vibrational energy, partitioned off from the rest of the chamber by a curtain wall dropped down from the chamber roof, and;

3) a substantially straight conduit passing from the upper region of the chamber outside the partitioned off area, through the chamber wall and entering an ajacent nebuliser delivery system.

Claim 2

A Cuboid aerosol generating chamber as claimed in claim 1 wherein the means of generating vibrational energy is a piezo electric transducer tuned to a frequency of from 1.5 MHz to 1.8 MHz.

Claim 3

A Cuboid aerosol generating chamber as claimed in claim 1 and 2 wherein the piezo electric transducer is located in the base half way between the centre and a corner of the chamber.

Claim 4

A Cuboid aerosol generating chamber as claimed in any previous claim wherein the partitioned off upper region of the chamber covers the quarter segment above the means of generating vibrational energy and extends down from the chamber ceiling by up to 30% of the total internal height of the chamber.

Claim 5

A Cuboid aerosol generating chamber as claimed in any previous claim wherein the end of the conduit passing between the upper region of the chamber and an adjacent nebuliser delivery system, within the chamber is located outside the partitioned quarter segment of the chamber and the conduit passes through the chamber wall at a shallow angle and a slight incline to enter an adjacent nebuliser delivery system.

Claim 6

A Cuboid aerosol generating chamber as claimed in any previous claim wherein the end of the conduit passing between the upper region of the chamber and an adjacent nebuliser delivery system rises at an angle of 12 plus or minus 2 degrees from the horizontal as it passes through the chamber wall at an angle 19 plus or minus 2 degrees to the wall.

Claim 7

A Cuboid aerosol generating chamber as claimed in any previous claim as described herein with reference to the accompanying drawings 1 to 3.