AU5193701A - A spray fan - Google Patents

Description

Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

°oooo *o*o* oo* *oo *g* Name of Applicant: The Minister for Primary Industries and Resources Actual Inventor: Geoff Furness Address for Service: MADDERNS, 1st Floor, 64 Hindmarsh Square, Adelaide, South Australia, Australia Invention title: A SPRAY FAN Details of Associated Provisional Application No: PQ 8021 dated 8 June 2000 The following statement is a full description of this invention, including the best method of performing it known to us.

PatAU131 This invention relates to a spray fan and in particular to the design of a fan used to distribute fluids as a finely atomised spray.

Such spray fans are commonly used for the distribution of agricultural chemicals such as insecticides and fungicides. These chemicals are normally mixed with water and distributed amongst the foliage of fruit trees, vines, field crops or the like by spray heads which produce finely atomised droplets. This atomisation ensures spray distribution which is as even as possible amongst the foliage, giving adequate coverage over the required surfaces of the plants and trees.

Such pest and fungicide sprays will not work adequately if distributed in large droplet sizes. Large droplets are ineffective in producing even distribution.

Accordingly, most spray delivery methods look to produce droplet sizes of 100 200 microns (volume mean diameter) in diameter or less.

In known spray delivery systems, fans are normally used in association with °ooo some form of atomising apparatus. High pressure pumps are used to force fluid S* through nozzles which produce a fine spray mist. This mist is either introduced into an air stream upwind of a fan, or may also be introduced on the downwind side of 20 the fan.

Known atomisers require high pressure pumps and fittings to produce the required atomised mist. Alternatively, fine mist can be produced through air shear by passing very high velocity air over liquid on a stationary surface, or atomisers S 25 may comprise a delivery head in the form of a porous rotating drum or disc spun at S.high rotational speeds to create the necessary fine spray.

Atomisers and associated fittings represent a significant proportion of the cost of any spray fan unit. There is also a significant cost for running the atomiser units.

Accordingly, it is an aim of this invention to provide an alternate means of producing a finely atomised mist from a spray fan.

In its broadest form the invention is a spray fan comprising: an axial flow fan, and a least one fluid outlet positioned to direct a fluid stream to the upwind side of said axial flow fan, said fluid stream having a component of direction that is radial with respect to the axis of said fan so as to result in said fluid travelling across the upwind side of said fan prior to it being drawn through said fan.

Preferably, the fluid outlet may comprise a low pressure jet or nozzle positioned proximate the outer periphery or the hub of the axial flow fan so that it directs the low pressure fluid stream radially towards or away from the hub of the fan. Further, the fluid outlet may be positioned between the hub and the periphery of the fan and comprise a jet or nozzle that produces a radial spray pattern around the jet or nozzle. In addition, the fluid outlet may be in the hub of the fan so that a fluid stream is directed away from the hub with the fluid stream rotating with the fan.

There is no requirement for the fluid outlet to produce any particular droplet size. In fact, very coarse droplets will not affect the operation of the invention.

It has been found that fluid flow which is caused to flow radially across the ooooo: upwind side of an axial flow fan will result in the droplets eventually being drawn through the fan. As a result of air flow shear forces acting through the fan, it has been found that even the largest droplet size will eventually exit the fan blades as a finely 25 atomised spray. Obviously, this atomised spray will be entrained within the air flow of the fan in the required manner.

It is not necessary for the fluid stream to travel the full distance to the hub of the axial flow fan. However, any fluid which does impact against the hub will generally be flung radially from the surface of the hub to then be entrained within the air stream directly upwind of the axial flow fan.

Preferably, the axial flow fan is surrounded by an annular shroud. Any fluid which is flung radially from the tips of the axial flow fan blades impacts against the inner surface of the annular shroud. It has been found that aerodynamic forces result in any fluid actually flowing upwind on the inner surface of the annular shroud to be sheared off the upwind side of the shroud and thus again be entrained in the air flow on the upwind side of the fan. Accordingly, there is minimal release of large droplets from the downwind side of the fan.

As can be seen from the description of the invention above, there is no need for high pressure pumps or fittings to produce finely atomised spray. However, the invention may benefit further from nozzles which produce a spray of fine droplet size. These fine droplets may be further atomised to produce a finely atomised spray as they pass through the fan.

Preferably, the fluid outlets direct the fluid stream in any direction radially with respect to the axis of the axial flow fan. However, with certain fan designs, it may be advantageous to have the stream angled so that it has an axial as well as a 20 radial component.

In an alternate form of the invention, the fluid outlet may be positioned proximate the hub of the axial flow fan so that it directs the fluid stream outwardly from the hub. Obviously, the velocity of the stream should not be sufficient so that 25 the fluid escapes past the periphery of the axial flow fan. In this case, in order to minimise the peripheral loss of fluid, the fan shroud may be sufficiently extended forward of the leading edge of the fans on the upwind side to redirect any fluid back into the region in front of the upwind side of the fan. A centrifugal pump may be incorporated into the fan hub to draw fluid from a reservoir and to provide the necessary pressure to produce a spray from the hub. The pump may have the hub as one component of the pump with another attached to the fan shaft.

In order to fully understand the invention, preferred embodiments are illustrated in the accompanying drawings in which: Fig 1 shows a side view of an axial flow fan comprising a hub, a plurality of fan blades and a drive motor and a cross sectional view of a fan shroud with jets or nozzles that discharge radially inwards towards the hub; Fig 2 is a schematic representation showing a cross section through a pair of adjacent fan blades with air flow and liquid movement with respect to those blades; Fig 3 shows a second embodiment of a spray fan using spray nozzles located between the hub and periphery of the fan that discharge radially around the nozzle; and Fig 4 shows a third embodiment of a spray fan that has jets or nozzles in the hub of the fan that discharge fluid radially outwards from the hub.

*o seen in Fig 1, fluid outlets 10 are positioned around the periphery of an axial flow fan 11. They direct fluid streams 12 to the upwind side of the fan 11 so that 20 the streams 12 are directed towards the hub 13 of the fan 11.

oo.ooi The fluid outlets 10 are mounted in the annular fan shroud 14. The number of fluid outlets 10 may vary depending on the diameter of the fan 11 used. The number of outlets 11 may preferably range from one to eight or there may be more 25 depending on the nature of the outlet.

Fig 1 shows the fluid stream 12 extending from the periphery of the fan 11 to its hub 13. Although this arrangement will allow all fluid from the outlets 10 to pass through the fan 11, it is not necessary that the fluid stream 12 actually impact the hub 13. The distance travelled by droplets from the fluid outlet 10 will depend on their velocity and size. Obviously, lighter particles may be entrained through the fan 11 at a much earlier stage and there will be wind shear forces directly upwind of the fan blades 15 which may result in some reduction in size of larger droplets.

Consequently, the fluid delivery pressure from the outlets 10 may be controlled so that minimal amount of fluid actually reaches the fan hub 13.

Fluid that reaches the hub 13 will be flung radially back into the air stream directly in front of the fan blades 15 to be entrained in the air flow through the fan 11.

Any fluid flowing along the surface of a fan blade 15 will be acted upon by air flow shear forces which will significantly reduce the droplet sizes. Consequently, fluid flowing from the downwind side of the fan 11 will be finely atomised.

Any fluid which flows radially from the tips of the fan blades 15 will impact against the inside surface of the fan shroud 14. Air flow in this region will tend to draw the fluid along the inside surface of the fan shroud 14 towards the upwind side of the fan 11 where it will then be sheared off and will then move radially towards the hub 13 of the fan 11. Accordingly, the majority of fluid flowing from the downwind side of the fan 11 will be finely atomised.

*As can be seen from the above description, adequate atomisation can be achieved without the use of high pressure pumps and fittings and atomising devices.

20 Accordingly, this significantly reduces the cost of such spray heads.

Fig 2 shows schematically the movement of a fluid stream 12 on the upwind side of the fan 11 and the entrainment and subsequent atomisation of the liquid through the fan blades 15. It is generally believed that the majority of the fluid flow 25 occurs in the air stream across the low pressure side 16 of each fan blade 15 and very close to the fan blade 15 surface and is atomised as a result of air shear forces so that it leaves near the trailing edge 17 of each fan blade 15 on the downwind side as a finely atomised spray.

Experiments have shown that the droplets delivered from the fluid outlets are generally confined to an air shear region directly in front of the leading edge 18 of the fan blades 15 prior to being drawn into the fan 11 by the air flow.

Fig 3 shows a second embodiment of the invention. In this embodiment, the fluid outlets comprise radial spray nozzles 19 that produce a radial fluid stream 12 around the periphery of each nozzle 19. This radial fluid stream 12 produces a circular spray pattern around each nozzle 19 which is in a plane that is substantially parallel to the plane of rotation of the fan 11. Between two to eight nozzles 19 may be spaced around the fan 11 although it has been found that four nozzles 19 provide the desired coverage over the area through which the fan blades rotate.

The nozzles 19 require only a low pressure fluid supply. The fluid supply pressure is generally not sufficient to cause large amounts of fluid to impact against either the hub 13 or the shroud 14. However, as with the first embodiment, any fluid contacting either of these components will be redirected back into the air stream.

Figure 4 shows a third embodiment of the invention. In this embodiment, the fluid outlets 20 are located in the hub 13. Each fluid outlet 20 is located generally near the leading edge of each fan blade 15. The outlets 20 direct a fluid stream 12 radially outwards towards the periphery of the fan 11. The necessary fluid conduits Smay be located within the hub 13 so that fluid is directed to the outlets 20. The 20 centrivical force applied to the fluid as it discharges from the outlets 20 may be S' sufficient to provide a low pressure suction effect which will draw fluid from a reservoir. In this manner, the hub and combined outlets 20 may act as a pump to create the necessary fluid discharge 12.

25 As an alternative to the first embodiment shown in Figure 1 but similar to the third embodiment shown in Figure 4, outlets 10 may be located adjacent the hub 13 so that the fluid flow 12 is directed radially outwards toward the periphery of the fan 11.

It will be clear from the above description that the invention has a significant advantage over and above existing spray fan delivery systems. However, it should be realised that the invention is not confined to the precise details of this embodiment and that variations that produce fluid distribution on the upwind side of an axial flow fan may still be within the scope of the invention.

Claims (13)

1. A spray fan comprising: an axial flow fan, and at least one fluid outlet positioned to direct a fluid stream to the upwind side of said axial flow fan, said fluid stream having a component of direction that is radial with respect to the axis of said fan so as to result in said fluid travelling across the upwind side of said fan prior to it being drawn through said fan.

2. A spray fan according to claim 1 wherein said fluid outlet comprises a low pressure nozzle.

3. A spray fan according to claim 2 wherein said nozzle is positioned proximate the periphery of said fan and directs said fluid stream towards the hub of said fan.

4. A spray fan according to either claim 1 or claim 2 wherein said nozzle is positioned intermediate the periphery and hub of said fan.

5. A spray fan according to claim 4 wherein said fluid outlet comprises a nozzle that directs said fluid stream radially around said nozzle.

6. A spray fan according to claim 5 wherein said radial fluid stream is in a plane that is substantially parallel to said fan's plane of rotation.

7. A spray fan according to any one of the preceding claims further comprising a shroud around the periphery of said fan.

8. A spray fan according to any one of the preceding claims wherein said fluid outlet comprises a spray nozzle.

9. A spray fan according to claim 1 or claim 2 wherein said fluid outlet is located on the hub of said fan so that said fluid stream is directed radially outwardly.

I I A spray fan according to claim 1 or claim 2 wherein said fluid outlet is'located adjacent the hub of said fan wherein said outlet directs said fluid stream towards the periphery of said fan.

11. A spray fan according to claim 3 wherein a plurality of said nozzles are spaced around the periphery of said fan.

12. A spray fan according to any one of claims 4, 5 or 6 comprising between two to eight said nozzles radially spaced around said fan.

13. A spray fan substantially as herein described with reference to the accompanying drawings. Dated this 8 th day of June, 2001 THE MINISTER FOR PRIMARY INDUSTRIES AND RESOURCES By its Patent Attorneys MADDERNS eeeoe