GB2298808A

GB2298808A - Twin-fluid nozzle for atomising a liquid

Info

Publication number: GB2298808A
Application number: GB9605526A
Authority: GB
Inventors: Joseph Henry Combellack
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-03-17
Filing date: 1996-03-15
Publication date: 1996-09-18
Also published as: GB9605526D0

Abstract

A twin fluid nozzle 11 able to be used for atomising a liquid by means of shear forces provided by a first fluid in a main conduit 24 onto a second fluid exiting from one or more secondary conduits 36 into the main conduit 24 a characteristic of the secondary conduit 36, such as the angle to the main conduit 24 or the size, shape or number of secondary conduits, being variable so as to ensure that substantial atomisation occurs for certain fluid flows. Twin fluid nozzle 11 also may include replaceable inserts 15 having the intersection of the main conduit 24 and secondary conduit 36 such that different inserts 15 have secondary conduits 36 with different characteristics so that atomisation can be controlled at different flow rates. The nozzle can have different output means including a foamer for producing foam or a spray head 17 for distributing the atomised fluid.

Description

TWIN FLUID NOZZLE FOR AGRICULTURAL AND INDUSTRIAL PURPOSES This invention relates generally to twin fluid nozzles in which one fluid assists spraying of another fluid.

In one particular form of the invention the twin fluid nozzle is able to be used with a gaseous fluid to atomise a liquid to assist spraying of the liquid at low flow rates. However the invention is not limited to atomisation of a liquid.

It is a common practice in agriculture to treat crops or pests by applying agrochemicals as a dilute liquid spray onto the crop or pest, mostly by using hydraulic nozzles. These nozzles generally have a body which incorporates functional components to enable the metering, atomisation and distribution of a liquid spray as well as providing a means of attachment to a movable spray unit. Hydraulic nozzles typically produce either an elliptical flat fan, solid cone or hollow cone of droplets.

There is an increasing demand by users of agrochemicals to use a lower application volume of spray in an endeavour to increase the area treated per unit time. For this to be achieved with hydraulic nozzles while maintaining a similar liquid operating pressure the liquid metering orifice of the hydraulic nozzle has to be reduced in area. A reduction in the area of the metering orifice leads to a propensity for it to block. Also smaller metering orifices which produce a consistent liquid flow rate are difficult to manufacture. Further it becomes more difficult to produce an acceptable spray pattern when the liquid flow rate is lowered below 0.5 litres per minute because it is increasingly troublesome to accurately manufacture a hydraulic spray tip having a suitable liquid metering orifice for such flow rates.

There is also a tendency for such low flow rate hydraulic nozzles to wear (i.e. increase the area of the orifice) more rapidly. In view of these difficulties users have shunned the use of low flow rate hydraulic nozzles.

A further problem with spray tips is that typically an increasing volume of driftable droplets (those less than 100 llm) is produced as the flow rate is decreased while operating at the same hydraulic pressure as the likelihood of droplet drift (defined as the "off target" movement of droplets) increases with a lowering of the liquid flow rate. Another problem with hydraulic nozzles is their inability to maintain a similar droplet spectra (defined as a statistical summary of the number and volume of each droplet produced) over a wide range of liquid flow rates. Generally a doubling in flow rate through a typical hydraulic spray tip necessitates a fourfold increase in hydraulic pressure but the droplet spectra becomes smaller as the liquid flow (and hydraulic pressure) increases.The user therefore has to carefully select a nozzle tip and pressure to deliver the required flow rate at the nominated travel speed to obtain the application volume needed for the task.

With hydraulic nozzles typically used in agriculture the selected operating parameters should be varied by no more than + 25% if spraying efficiency and environmental safety is to be maintained. Therefore presently a user spraying a range of pests in a range of crops will have to frequently change spray tips to accommodate changes in the required application volume and droplet spectra. The use of a range of hydraulic nozzles and spray tips is not only expensive but time consuming in attaching different nozzles to the movable spray unit and hazardous when changing nozzles after spraying poisons such as pesticides or herbicides..

Twin fluid nozzles used in agriculture mix air and liquid, typically in an internal chamber, before they are dispersed through a relatively large circular orifice and onto a modified anvil nozzle tip. These nozzles are able to maintain a consistently similar droplet spectra over a range of flow rates by changing the air to liquid ratios. They are also able to be used at low liquid flow rates without a propensity to block as the orifice is relatively large and are able to reduce drift by air entrainment of small droplets. Also spray quality can be adjusted from a coarse to a fine spray at a given liquid flow rate by varying the air and liquid pressures. Twin fluid nozzles therefore offer a flexible and feasible way of addressing the challenge of reducing drift while increasing operational efficiency through lower application volumes.

However, generally all twin fluid nozzles use an anvil onto which the liquid is forced at pressure to "break up" the liquid and an air flow carries the partially atomised liquid to a shaped spraying deflector anvil that further atomises the liquid and distributes the atomised liquid over a predetermined spray pattern. The use of anvils requires high pressures and high flow rates. A presently commercialised twin fluid nozzle system requires a high air volume ( > 25 litres/min./nozzle) at pressures up to 180 kPa and even up to 276 kPa if fine sprays are to be produced. Another commercialised system utilises pressures up to 200 kPa and air volumes usually between 30 and 50 litres per minute.It is necessary to use a piston or rotary screw compressor to achieve pressures over 150 kPa. Both are expensive to purchase and to run and the piston compressors are not efficient nor durable at lower pressures, < 200 kPa.

Therefore the air pressure range (69 to 276 kPa) tested and suggested for some commercialised systems is not very practical for field use. As a compromise the commercialised systems normally use a rotary vane compressor to produce the necessary air volume but these can only generate pressures up to around 150 kPa. These compressors require at least a 20 HP engine to provide sufficient air volumes (of up to 50 litres/min/nozzle) on a typical 30 meter boom of a movable spray unit. Furthermore, the two commercialised systems are unable to accommodate a "tum down ratio" of much over two, (i.e. maintain a similar droplet spectra for a doubling of liquid flow), and then only by adjusting both liquid and air pressures.

It is also a common practice to delineate bouts when spraying, fertilising or sowing broad acre crops in many countries to reduce errors in overlapping. This has been achieved by numerous systems, one of the most common is the use of foam blobs. The foam has typically been generated by bubbling air through diluted foamers (a chemical mixture that produces foam) and then compressing the bubbles into compressed foam by pushing them through a long tube which extends to the end of the boom. More recently end boom foam generators have been used. These mix air with the diluted foamer at the end of the boom in a device known as a foam generator. The design of this device is critical to efficient foam production.

One object of this invention is to provide a nozzle which is suitable for the application of a wide range of types of agrochemicals over a wide range of application volumes, and for a wide range of types of ground operated equipment that currently use hydraulic nozzles such as from agricultural boom sprayers to air blast orchard sprayers.

It is also an object of the invention to provide for use on boom sprayers and other agricultural machinery, a foam generator which is reliable and capable of sustained operation whilst delivering adequate volumes of foam over a wide range of environmental conditions.

A further object of the invention is to provide a twin fluid nozzle that can be used with lower air flows to conventional twin fluid nozzles and with air pressures accommodated by a rotary vane compressor and which is able to accommodate a "turn down ratio" of two to three without adjustment to air pressure as well as being useable with rotary screw or piston compressors.

A still further object of the invention is to provide a twin fluid nozzle which can have a plurality of different attachments to allow it to function in a plurality of different modes.

DISCLOSURE OF THE INVENTION It has been realised, in accordance with the invention, that one way of achieving low delivery flow rates is to shear the emitted spray liquid with a directed air stream and by presenting the liquid in different ways vary the shear and thus the degree of atomisation.

Further, droplet velocity is also able to be varied by manipulating the air flow and the direction the liquid is presented to the airstream.

According to one form of the invention there is provided a twin fluid nozzle for providing variable shear forces by a first fluid on a second fluid, comprising a body with a main conduit having a fluid entry port and a fluid exit port whereby a first fluid is able to be fed into the fluid entry port and pass along the main conduit; the body further including at least one secondary conduit leading into the main conduit and providing a path for a second fluid to the main conduit whereat the flow of the first fluid is able to provide shear forces on the second fluid entering the main conduit; the nozzle also including a varying means which is able to vary a characteristic of the secondary conduit so as to vary the shear forces provided by the first fluid on the second fluid.

According to another form of the invention there is provided a twin fluid nozzle for providing liquid atomisation, comprising a body with a main conduit having a fluid entry port and a fluid exit port whereby a gaseous fluid is able to be fed into the fluid entry port and pass along the main conduit; the body further including at least one secondary conduit leading into the main conduit and providing a path for a liquid to the main conduit, the at least one secondary conduit being at an angle to the main conduit, dependent on the fluid pressures, so as to produce shear forces by the gaseous fluid on the liquid at each of the intersections of the main conduit and the at least one secondary conduit such that there is substantial atomisation of the liquid.

In another form of the invention there is provided an insert suitable for a twin fluid nozzle as defined in claims 1 or 13, and comprising a main conduit along which a first fluid can flow and at least one secondary conduit for feeding a second fluid into the main conduit such that shear forces provided by the first fluid on the second fluid at each of the intersections of the main conduit and the at least one secondary conduit provide substantial atomisation of the second fluid.

In still yet another form of the invention there is provided a foam generator comprising a body with a main fluid flow passage and a plurality of secondary conduits leading into the main conduit at an angle such that at particular flows of gas along the main conduit and of foaming liquid along the secondary conduits, the shear forces provided by the gas on the foaming liquid at the intersection of the main and secondary conduits causes substantial atomisation of the foaming liquid, the exit of the main conduit connecting with a foaming filter having a large surface area to enhance the incorporation of the residual air to form foam bubbles.

In one embodiment of the invention there is provided a multifunctional air/liquid nozzle (hereinafter referred to as a MALAN) which varies the air shear by varying the direction which the liquid enters the air stream through the use of a plurality of nozzle inserts having differently directed liquid entry passage(s). The size and shape of the air passage varies the volume of air used whilst air pressure varies its velocity. The size, number, shape of the liquid entry passages and the angle of the liquid entry passage(s) to the airstream varies the volume of liquid entering the airstream and the amount of air shear to which it is subjected which in turn governs droplet spectra and droplet velocity. The air shear results in the liquid being mostly atomised in the nozzle insert.For use as an agricultural nozzle the atomised spray can be subsequently distributed via an anvil spray tip whose orifice size is important in determining air flow, and thus to some extent air velocity. The orifice exit onto the impact face needs to be below the line of the transverse cut and the impact face needs to be of a specific shape to maximise distribution. The use of specially fabricated flat fan or comb spray tips is also possible and may be preferred in some situations.

A three fold volume of spray liquid can be atomised into a similar droplet spectra if a constant air pressure is maintained within the range 75 to 130 kPa. If air pressures up to 300 kPa are used then a similar spectra can be generated over an eight fold change in flow rates by adjusting both air and liquid flow rates. Experimentation has shown that droplet drift is reduced compared to a conventional hydraulic nozzle operating at the same flow rate.

Experimentation has also shown that spray retention on plants is similar to that obtained with a conventional flat fan hydraulic spray tip when delivering the same application volume. The said nozzle has been shown to "include" air within the droplets when using certain spray solutions. When used to generate foam for bout marking the atomised liquid, which contains a very high level of air "inclusions", is directed onto a filter with a large surface area to maximise the entrainment of residual air with the liquid to thus maximise foam volume. In industrial situations nozzles can be developed to accommodate a wide range of flow rates and to produce a range of droplet spectra. By increasing air pressure, and thus volume, for the same flow rate the droplet spectra becomes smaller.By increasing the diameter of the air passage as well as the orifice in the spray tip the volume of air utilised is increased and droplet velocity then increases relative to air pressure. Also the small droplets ( < 1 00;im) become less prone to drifting. There are therefore an infinite number of possibilities for the invention.

One embodiment of the invention accordingly provides a nozzle for use in applying agrochemicals and other liquids applied by agricultural persons through the use of a boom sprayer, orchard sprayer and other sprayer units which use nozzles, and comprises a nozzle body which accommodates an atomising insert that has one or more fluid feed conduits, said feed conduits communicating with the main atomising point by having a fixed conduit for the air but a variably aligned liquid feed secondary conduit. The secondary conduit ensures that the liquid communicates with the air at different intersecting angles to vary the shear and therefore the droplet sizes produced and the velocity of the droplets, the said device leads to a distribution tip designed to produce a flat fan, solid or hollow cone of droplets (spray).

The intersection of the air and liquid conduits can be at any angle from each other so that the liquid flow ranges from being with the air stream to being against the air stream in the atomising insert. By varying the intersecting angle of the liquid and the air stream from 165 into the air stream so that the liquid flows and provides a very high shear configuration, to 150 so that the liquid flows downwards with the air stream and provides a low air shear configuration, the droplet sizes produced, and their velocity, are greatly altered. In general the greater the air shear the smaller the droplets and the lower is their velocity, and the lower the air shear the greater the droplet size and their velocity. A range of atomising inserts with differing angles of secondary conduits to the main conduit can therefore be used to provide varying air shear. In embodiments of the invention the atomising insert had a neck portion recessed about 2.5 mm which need not be aligned with the inlet port in the nozzle body to ensure liquid flows from a liquid inlet chamber into the secondary conduit in the atomising insert as the liquid inlet chamber formed between the neck portion of the insert and the bore of the nozzle body can be sealed top and bottom of the inlet port with "0" rings and allow liquid to flow into the secondary conduit in the insert regardless of its position relative to the inlet port.

The size and shape of a liquid orifice at the exit of the secondary conduit in the atomising insert device can be varied in diameter or in numbers to regulate the flow of liquid.

The shape of both the main (air) and secondary (liquid) conduits can be varied from circular to substantially square or rectangular at the point of intersection of the two fluids.

The nozzle spray tip should include an orifice in fluid communication with the main air conduit and should be designed to enable even distribution of droplets onto a target surface.

Nozzle tip spacing will vary with the sprayer but for boom sprayers should be nominally 500 mm and the operating height around 350 mm from the target.

The nozzle unit may include a clamping arrangement for securing it to the unit or tube or frame of the sprayer, for example an air delivery tube forming part of or supported by such a frame.

It has been realised, in accordance with an embodiment of the invention, that one way of achieving efficient foam production is to atomise the foaming liquid with a high shear entrained air stream. A number of other systems are known to exist but do not utilise the concept of high shear as used in this invention.

An embodiment of the invention accordingly provides the basis for a foam generator and comprises a body which defines a main fluid flow passage and a pair of fluid feed passages, said feed passages communicating with main fluid passage and intersecting at an angle sufficient for the respective gas (air) and liquid (foamer) fluids transversing the feed conduits to mix, with virtually complete atomisation of the liquid (foamer) in the main feed conduit, the atomised liquid (foamer) and air are then passed along the main conduit which leads onto a specially selected filter having a large surface area to enhance the incorporation of the residual air into the droplets thus forming bubbles, the said bubbles are then compressed by forcing them through a tube, whose size and length may be adjusted to produce the optimum quality of foam, and on into an accumulator, whose size and shape is selected to ensure that appropriate blob size and frequency are obtained before being discharged.

The air and liquid feed conduits may be round or substantially rectangular having dimensions which optimises the production of appropriate droplet sizes and velocities to maximise air inclusion into the liquid to form bubbles on the filter.

The foam generator unit preferably includes two parts which can be separated to allow the filter to be removed and cleaned.

The foam generator unit preferably further includes a pump whose flow output can be adjusted to control the flow rate of the liquid foamer into the foam generator. Preferably attached between the pump and the foam generator is a one way valve which has a pressure rating sufficient to prevent liquid siphoning from the tank when not operating.

BRIEF DESCRIPTION OF THE DRAWINGS The embodiments of the invention will be further described, by way of example, using the accompanying drawings, in which: Fig. 1 is a side sectional view of a variable shear twin fluid nozzle unit according to a first embodiment of the invention.

Fig. 2A and 2B are partial side sectional views of variations of the angle of secondary conduits of the twin fluid nozzle unit of Fig. 1.

Fig. 3 is a side sectional view of a foam generator in accordance with a second embodiment of the invention.

Fig. 4A is a side sectional view of the foaming filter of the foam generator of Fig. 3 along the line 4A - 4A of Fig. 4B.

Fig. 4B is a cross sectional view of the foaming filter of the foam generator of Fig. 3.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION In Fig. 1 is shown an air liquid nozzle 11 comprising a nozzle body 12 having a cylindrical bore 19 able to receive a substantially cylindrical insert 15. An intermediate body 13 is mountable on the nozzle body 12 by a screw thread and includes a cylindrical bore 20 which aligns with the bore 19 ofthe nozzle body 12. The intermediate body 13 has a stepped internal lip at one end of its bore 20 so as to form a shoulder 22 which engages external flanges 25 at one end ofthe insert 15 such that when the insert 15 is inserted into the bore 20 of intermediate body 13 and through to the bore 19 of the nozzle body 12 the external flanges 25 engage the shoulders 22 of the intermediate 13 and limit the movement of the insert 15 to correctly position the insert 15.

The nozzle body 12 at one end has an air inlet port 31 which aligns with and feeds to a bore 19 in which is located the insert 15. The insert has a central main cylindrical conduit 24 extending through its length. Therefore, air supplied at the inlet port 31 is able to enter the main conduit 24 through an end inlet 23 of the insert 15 and pass along the main conduit 24 to an outlet 26 at the other end of the insert 15 protruding from the other end of the intermediate body 13. Generally the diameter of the air path including an inlet air feed (not shown) which fits into the air inlet port 31, and the main cylindrical conduit 24 are sized with a constant diameter to minimise turbulence of the air flow.

The nozzle body 12 further includes a liquid inlet port 32 at right angles to the air inlet port 31 and which feeds to the main conduit 24. The substantially cylindrical insert 15 has near its inlet 23 a narrower cylindrical neck portion 27 such that when the insert 15 is in position in the bore 19 of the nozzle body 12, the narrower neck portion 27 and the inner walls of the bore 19 form an annular liquid inlet chamber 28. "0" rings 29 and 30 on both sides of the neck portion 27 ensure sealing of this liquid inlet chamber 28 when the insert 15 is in position in the bore 19 of the nozzle body 12. Also when in position, the liquid inlet port 32 of the nozzle body 12 feeds directly into the liquid inlet chamber 28 formed between the neck portion 27 of the insert 15 and the bore 19 of the nozzle body 12.

The insert 15 includes secondary conduits 36 which lead from the neck portion 27 of the insert 15 to the internal central main conduit 24 of the insert 15. Thereby, in operation, air enters the air inlet port 31 of the nozzle body 12 and enters the inlet 23 to form an air stream down the main conduit 24 towards the outlet 26 of the insert 15 and liquid enters the liquid inlet port 32 of the nozzle body 12 and feeds to the liquid inlet chamber 28 formed by the neck portion 27 ofthe insert 15 and the internal wall ofthe bore 19 ofthe nozzle body 12 which then feeds into the secondary conduits 36 and leads to secondary conduit exits 37 at the intersection of the secondary conduit 36 with the main conduit 24. As the liquid is being fed through the secondary conduit exits 37 into the air stream of the main conduit 24, the air stream is able to provide shear forces on the liquid to provide substantial atomisation of the liquid.

The insert 15 includes a variable number of passages, with the main conduit 24 for the air and from one to four secondary conduits 36 for the liquid (only two are shown). The liquid inlet chamber 28 can also be varied in shape from cylindrical to substantially square or rectangular but is shown as cylindrical in the illustration. As shown as angles a, b, c, d, e, and fin Figures 2a and 2b, the angle at which the secondary conduits 36 meets the main conduit 24 can be varied from around 15" to 1650, but this limitation is only a manufacturing limitation.

In order to distribute this substantially atomised liquid a spray tip 17 is fixed at the outlet 26 of the insert 15 and is retained in position by a spray tip connector 14 that has a central opening through which the spray tip 17 extends and is retained in position by the internal step of the spray tip connector 14 engaging with a lower flange of the spray tip 17.

The spray tip connector 14 is connected to the intermediate body 13 by a bayonet connection onto protruding pins 41 ofthe intermediate body 13, the spray tip connector 14 including its own external ears 46 to facilitate the use of a users fingers to connect the spray tip connector 14 to the intermediate body 13. The spray tip 17 includes a central bore 49 which aligns with the main conduit 24 of the insert 15, such that the substantially atomised spray passes through the bore ofthe spray tip 17 to the exit orifice 47 which limits the flow and directs the flow onto an anvil 48 to provide the desired distribution pattern of the atomised spray.

The spray tip cap connector is fitted by means of compression and sealed with a seal gasket 59. The spray tip 17 can vary in shape and size, in this instance a deflector spray tip which gives a flat fan spray is shown.

One example of the multifunctional air liquid atomising nozzle (MALAN) of the invention maintained a nominal volume median droplet diameter (VMD) of around 400 llm over a liquid flow rate range of 0.25 to 1.5 1/min, i.e. half the recorded droplet diameters were above 400 llm while half were below that figure. The MALAN produced substantially less drift then standard flat fan but marginally more than low drift nozzles. Spray retention on plant species Beta vulgaris, Allium cepa and Brassica oleracea showed that the MALAN was equivalent to a conventional flat nozzle and that both effected about twice as much retention as a flat fan turbo nozzle. The MALAN provides the means for subtle variations in droplet spectra and velocity, by varying air shear, and thus can vary spray capture on different plant surfaces.The MALAN can be used in the field or as a very valuable research tool.

Referring to Fig. 3 and Figs. 4A and 4B, there is shown a foam generator 51 according to an embodiment of the invention which includes the nozzle body 12 of the air liquid nozzle 11 into which is able to be received an insert 16 which is a foreshortened version of the insert 15 of the air liquid nozzle 11. Essentially though the part of the insert 15 within the nozzle body 12 of the air liquid nozzle 11 is substantially the same as the part of the insert 16 within the nozzle body 12.However the end of the insert 16 extending out of the nozzle body 12 has an external flange 61 which engages with the end of the nozzle body 12 around the bore 19 and locates the insert 16 in the correct position such that the liquid inlet port 32 of the nozzle body 12 leads into an annular liquid inlet chamber 28 formed similarly as in the air/liquid nozzle 11 and similarly feeds into secondary conduit 36 and into the main conduit 24 of the insert 16. The insert is similarly operative, with the liquid being a foaming agent that is atomised and sent along the main conduit 24 to a foamer body 52 which is screw threaded onto the end ofthe nozzle body 12 at the same position as the intermediate body 13 is screw threaded on to the nozzle body 12 for the air/liquid nozzle 11.The foamer body 52 includes a frusto-conical filter 53 extending in the same direction as the main conduit 24 of the insert 16 such that the atomised spray enters into a hollow centre 61 of the frusto-conical filter 53. The hollow centre 61 of the frusto-conical filter 53 includes a plurality of longitudinal ridges 62 with holes 64 therebetween allowing fluid flow through to a foam compression chamber 54 which wholly encloses the frusto-conical filter 53. The frusto-conical filter 53 includes a plurality of external circular flanges 63 spaced along the length and perpendicular to the length of the frusto-conical filter 53. The internal ridges 62 together with the external flanges 63 of the frusto-conical filter 53 form a maximisation of surface area to facilitate foaming of the foaming agent.The resultant foam in the foam compression chamber 54 then exits through the outlet 55 of the foamer body 52 at the end distant to the connection to the nozzle body 12 and feeds to a compression tube 56 (not shown) which is of sufficient length and size to compress the resultant foam into a useable density which can be used for providing bout markers or for other purposes as required.

The foam generator 51 of the form illustrated in the drawing has been designed for use with a 12 volt compressor nominally delivery 28 of 30 litres of air per minute, the main conduit 24 of the insert 16 is 4 mm in diameter and the secondary conduits are 1.5 mm in diameter. It has been found that these need to be changed to optimise foam production from compressors with greater output or for higher liquid flow. Further the shape of the passages and the angle at which the two fluids meet at the secondary conduit exits 37 has been found to affect the efficiency of foam production and the quality of foam delivered. Cylindrical conduits have been shown in the drawings but those that are substantially rectangular in cross section have been found to be more efficient in some circumstances.Foam production has been found to be generally more efficient when the angle of intersection of the secondary conduits 36 and the main conduit 24 is at right angles to or at an angle such that the liquid exits partially against the airstream. The angle is important as it influences atomisation and the velocity of the droplets produced which in turn affect the amount and quality of foam produced.

TEST RESULTS In the results presented herein the insert 15 had a main conduit 24 diameter of 4 mm, and there were two secondary conduits 36 each with a diameter of 1.5 mm and drilled at an angle of 30 to the insert axis. The stainless steel nozzle spray tip 17 had a 1.8 mm exit orifice 47. It has been found that the MALAN foam generator unit is effective at mixing the two fluids, air and liquid (foamer), at low pressures (typically less than 40 kPa) to enable effective foam generation and good quality foam at low flow rates (typically 150 to 500 mvmin).

It has also been found that the diameter of the air passage and the diameter and angle of the liquid passage are important for efficient foam production. For the 12 volt compressors tested the diameter of the air passage should be around 4 mm and be substantially aligned with the main passage. The diameter of the two liquid ports should be around 1.5 mm and be substantially at right angles to the airstream if a flow rate range of 150 to 500 ml/min are to be converted into foam It is recognised that the angle and diameter of the liquid inlet ports need to be altered if a higher or lower air flow are used.

Droplet spectra and their velocity were measured using a Particle Measuring System type PDPS analyser and a two dimensional type 2D GAl probe placed 350 mm below the nozzle spray tip. The whole of the spray was measured by moving the nozzle across the fan in 100 mm intervals across its long axis and by moving the nozzle through the spray cloud at 50 mm/s. Measurements were made using a 90% a.i.nonyl phenol ethoxylate at 0.1% v/v in tap water.

Drift measurements were made in the wind tunnel at Silsoe Research Institute. A wind speed of 3.0 rn/s was used with the MALAN at 350 mm from the tunnel floor which was covered with an artificial turf. The spray solution used comprised 0.1% v/v 90% a.i.nonyl phenol ethoxylate at 0.1% v/v in tap water plus 1.0 g/l of the fluorescent dye "Green S".

There was a 2 meter distance between the nozzle and the 2 mm plastic tubing used as a collector. The collectors were each 2 meters in length, thus the frill width of the tunnel, and were attached 100, 200, 300 and 400 mm above the floor ofthe tunnel. The drift, from a 10 second spray period, was estimated from the collected material on the plastic tubes using a MNSE Spectroplus flourimeter.

Table 1: Droplet spectra for MALAN having insert with two liquid inlet holes facing at a downstream angle to the air flow and when spraying at a range of flow rates at three air pressures (measured by scanning one half of the spray pattern)

Air Flow rates, 1. per min % of spray volume pressure VMD, m Velocity m/s kPa liquid air < 200 m 2-500 m > 500 m 75 0.3 21 545 1.9 4.08 5703 3.2 75 0.5 11.5 564 1.3 39.4 59.3 3.3 75 0.7 7 557 1.4 38.8 59.8 3.4 75 0.9 3 547 1.3 40.4 58.3 3.5 100 0.4 21 508 2.2 46.1 51.7 3.5 100 0.6 11.5 505 1.7 47.1 51.2 3.4 100 0.9 5.5 522 1.5 44.7 53.8 3.8 100 1.2 1.5 515 1.7 45.4 52.9 3.5 130 0.6 17 496 2.2 48.6 49.2 3.9 130 0.9 8 485 2.2 56.4 47.4 4 130 1.2 3 456 2.3 58.5 39.2 3.2 130 1.5 1 498 2.3 48 49.7 4.1 5 As can be seen from the above table a nozzle in accordance with an embodiment of the invention is operative at and below the 130 kPa range such that a rotary vane compressor can be used. Also the "turn down ratio" is nearly 3 with the same low air flow. For example at a given air pressure of 75 kPa the liquid flow rate can vary from 0.3 to 0.9 litres per min (a ratio of three) while maintaining a similar spectra.

Claims

I claim as my invention:

1. A twin fluid nozzle for providing variable shear forces by a first fluid on a second fluid, comprising a body with a main conduit having a fluid entry port and a fluid exit port whereby a first fluid is able to be fed into the fluid entry port and pass along the main conduit; the body further including at least one secondary conduit leading into the main conduit and providing a path for a second fluid to the main conduit whereat the flow of the first fluid is able to provide shear forces on the second fluid entering the main conduit; the nozzle also including a varying means which is able to vary a characteristic of the secondary conduit so as to vary the shear forces provided by the first fluid on the second fluid.

2. A twin fluid nozzle as defined in claim 1 wherein the varying means is able to vary the shear forces provided by the first fluid on the second fluid by providing a variation in the number, size or shape of secondary conduits able to feed the second fluid into the main conduit.

3. A twin fluid nozzle as defined in claim 1 or 2 wherein the varying means is able to vary the shear forces provided by the first fluid on the second fluid by varying the angle that the secondary conduit feeds the second fluid into the main conduit.

4. A twin fluid nozzle as defined in claim 1, 2 or 3 wherein the varying means is able to vary the size and shape of the orifice of the secondary conduit exit into the main conduit.

5. A twin fluid nozzle as defined in any one of the preceding claims wherein the nozzle includes an outer casing and the varying means comprises a replaceable insert able to be received within the outer casing, whereby each insert comprises the part of the body with the main conduit and the at least one secondary conduit leading into the main conduit and with a particular set of characteristics such that selection of different inserts with different characteristics allows variability of the shear forces provided by the first fluid on the second fluid.

6. A twin fluid nozzle as defined in claim 5 for providing liquid atomisation wherein a gas is able to pass along the main conduit and a liquid pass along the at least one secondary conduit into the main conduit whereat the shear forces provided by the gas flow on the liquid flow entering the main conduit provides substantial atomisation of the liquid.

7. A twin fluid nozzle as defined in claim 6 wherein the insert comprises a plurality of secondary conduits able to feed the liquid into various sides of the main conduit whereat the shear forces provide substantial atomisation of the liquid.

8. A twin fluid nozzle as defined in claim 5, 6 or 7 wherein the nozzle includes a liquid inlet chamber between the insert and the outer casing when the insert is in position in the outer casing and the plurality of secondary conduits of the insert extend from the outside surface adjacent the liquid inlet chamber such that liquid fed to the liquid inlet chamber can feed to the plurality of secondary conduits.

9. A twin fluid nozzle as defined in claim 8 wherein the liquid inlet chamber substantially circumferentially surrounds a portion of the insert when the insert is in position in the outer casing.

10. A twin fluid nozzle as defined in any one of the preceding claims wherein the nozzle includes a distribution head connected to the fluid exit port of the main conduit which is configured to spray the emerging fluid over a predetermined spray pattern.

11. A twin fluid nozzle as defined in claim 6 wherein the nozzle includes a foam body having a filter with a large surface area, the filter being connected to the fluid exit port of the main conduit and air being the first fluid and foaming liquid being the second liquid such that foaming liquid provided into the secondary conduits and fed into the main conduit is substantially atomised by the air and the substantially atomised foaming liquid is fed to the filter whereat the large surface area enhances the incorporation of the residual air to form foam bubbles.

12. A twin fluid nozzle as defined in any one of the preceding claims wherein one of a plurality of functional output devices can be fitted to the nozzle and fluidly connect with the fluid exit port of the main conduit.

13. A twin fluid nozzle as defined in claim 12 wherein the functional output devices are a foamer body for producing foam or a spray distribution head for distributing the substantially atomised liquid.

14. A twin fluid nozzle for providing liquid atomisation, comprising a body with a main conduit having a fluid entry port and a fluid exit port whereby a gaseous fluid is able to be fed into the fluid entry port and pass along the main conduit; the body further including at least one secondary conduit leading into the main conduit and providing a path for a liquid to the main conduit, the at least one secondary conduit being at an angle to the main conduit, dependent on the fluid pressures, so as to produce shear forces by the gaseous fluid on the liquid at each of the intersections of the main conduit and the at least one secondary conduit such that there is substantial atomisation of the liquid.

15. A twin fluid nozzle as defined in claim 14 wherein the body comprises a plurality of secondary conduits able to feed the liquid into various sides of the main conduit whereat the shear forces provide substantial atomisation of the liquid.

16. A twin fluid nozzle as defined in claim 14 or 15 wherein the body of the nozzle includes a liquid inlet chamber and the plurality of secondary conduits extend from the liquid inlet chamber such that liquid fed to the liquid inlet chamber can feed to the plurality of secondary conduits.

17. A twin fluid nozzle as defined in claim 16 wherein the liquid inlet chamber substantially surrounds a portion of the main conduit.

18. A twin fluid nozzle as defined in claim 14, 15, 16 or 17 wherein the nozzle includes a distribution head connected to the fluid exit port of the main conduit and which is configured to spray the emerging fluid over a predetermined spray pattern.

19. A twin fluid nozzle as defined in claim 14 wherein the nozzle includes a foam body having a filter with a large surface area, the filter being connected to the fluid exit port of the main conduit and air being the first fluid and foaming liquid being the second fluid such that foaming liquid provided into the secondary conduits and fed into the main conduit is substantially atomised by the air and the substantially atomised foaming liquid is fed to the filter whereat the large surface area enhances the incorporation of the residual air to form foam bubbles.

20. A twin fluid nozzle as defined in any one of the preceding claims wherein one of a plurality of functional output devices can be fitted to the nozzle and fluidly connect with the fluid exit port of the main conduit.

21. A twin fluid nozzle as defined in claim 20 wherein the functional output devices are a foamer body for producing foam or a spray distribution head for distributing the substantially atomised liquid.

22. A twin fluid nozzle as defined in claim 14 to 19 wherein the at least one secondary conduit feeds the second fluid at an acute or an obtuse angle to the first fluid in the main conduit.

23. An insert suitable for a twin fluid nozzle as defined in claims 1 or 14, and comprising a main conduit along which a first fluid can flow and at least one secondary conduit for feeding a second fluid into the main conduit such that shear forces provided by the first fluid on the second fluid at each of the intersections of the main conduit and the at least one secondary conduit provide substantial atomisation of the second fluid.

24. A foam generator comprising a body with a main fluid flow passage and a plurality of secondary conduits leading into the main conduit at an angle such that at particular flows of gas along the main conduit and of foaming liquid along the secondary conduits, the shear forces provided by the gas on the foaming liquid at the intersection of the main and secondary conduits causes substantial atomisation of the foaming liquid, the exit of the main conduit connecting with a foaming filter having a large surface area to enhance the incorporation of the residual air to form foam bubbles.

25. A foam generator as defined in claim 24 wherein the foaming filter comprises a hollow body with a plurality of internal ridges, a series of holes in the body and a plurality of external ridges, wherein substantially atomised is received in the hollow body and pass through the holes and the internal and external ridges provide surface area to enhance the incorporation of the residual air to form foam bubbles.

26. A foam generator as defined in claim 25 wherein the foaming filter is substantially frusto-concial, with the internal ridges extending at an angle to the extension of the external ridges.

27. A foam generator as defined in claim 26 wherein the internal ridges extend along the length and the external ridges are spaced circular ridges with the holes located in the spaces between the internal and external ridges.

28. A twin fluid nozzle substantially as herein described with reference to and as shown in the accompanying drawings.

29. A foam generator substantially as herein described with reference to and as shown in the accompanying drawings.

30. Any novel feature or combination of features disclosed herein.