WO2022260537A1

WO2022260537A1 - Apparatus and method to generate a negative pressure

Info

Publication number: WO2022260537A1
Application number: PCT/NZ2022/050068
Authority: WO
Inventors: David Godfrey Kay
Original assignee: David Godfrey Kay
Priority date: 2021-06-08
Filing date: 2022-06-07
Publication date: 2022-12-15

Abstract

An apparatus for generating a negative pressure has an upper flow director, an inlet for directing a driving liquid into the upper flow director, a lower flow director in fluid communication with the upper flow director, and a vacuum port. The upper flow director is shaped to induce a first spiralling flow in which the driving liquid flows in a generally inwardly and downwardly spiralling manner about a first spiral axis. The lower flow director is shaped to induce a second spiralling flow in a generally inwardly and upwardly spiralling manner about a second spiral axis. Flow of the driving liquid through the apparatus generates a negative pressure at the vacuum port.

Description

APPARATUS AND METHOD TO GENERATE A NEGATIVE PRESSURE

FIELD OF THE INVENTION

An apparatus and method utilising a flow of liquid to generate a negative pressure. In particular, an apparatus and method generating two generally oppositely spiralling flows in the flow of liquid.

BACKGROUND

Negative pressure and vacuum generators have innumerable applications across widespread industries. They are especially widely used in manufacturing and for packaging of products and parts. Where high negative pressures are required and/or where high-volume fluid displacement is required, existing methods for generating a negative pressure most commonly utilise mechanical vacuum pumps. Mechanical pumps rely on moving parts to displace gases to create the vacuum, must include seals to contain the vacuum, and typically require an electrical power source. Moving parts and seals are susceptible to wear and malfunction and require regular maintenance.

There are some existing devices, for example ejectors, with minimal moving parts that utilise fluid flow through low pressure venturi tubes to generate a pressure drop. These are most commonly used to mix two or more fluids. However, these devices are generally only suitable for very low volume and/or low- pressure applications.

It is an object of at least preferred embodiments of the present invention to address one or more of the above-mentioned disadvantages and/or to at least provide the public with a useful alternative.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally to provide a context for discussing features of the invention. Unless specifically stated otherwise, reference to such external documents or sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

SUMMARY OF THE INVENTION

In a first aspect, the present invention broadly consists in an apparatus for generating a negative pressure, comprising an upper flow director, an inlet for directing a driving fluid into the upper flow director, a lower flow director in fluid communication with the upper flow director, and a vacuum port. The upper flow director is shaped to induce a first spiralling flow in which the driving liquid flows in a generally inwardly and downwardly spiralling manner about a first spiral axis, and the lower flow director is shaped to induce a second spiralling flow in a generally inwardly and upwardly spiralling manner about a second spiral axis. Flow of the driving fluid through the apparatus generates a negative pressure at the vacuum port.

In an embodiment, the upper flow director generally narrows from a wider inlet end to a narrow outlet end. For example, the upper flow director may be shaped as a funnel. In an embodiment, a tapering wall of the upper flow director is substantially straight. Alternatively, a tapering wall of the upper flow director may be curved.

In an embodiment, the lower flow director generally widens from a narrow inlet end to a wider outlet end. For example, the lower flow director may be shaped as an inverted funnel.

In an embodiment, a wall of the lower flow director has a curved profile. The curved wall of the lower flow may have a convex inner surface. The curved wall of the lower flow may have the curve of a hyperbola.

In an embodiment, the upper flow director has an outlet that is coincident and/or coaxial with an inlet for the lower flow director.

In an embodiment, the walls of the upper flow and lower flow director may be contiguous.

In an embodiment, the apparatus may comprise a throat positioned at or between the outlet of the upper flow and the inlet lower flow director form a throat. In an embodiment, the outlet of the upper flow and the inlet lower flow director form a throat. The throat may comprise a cylindrical member.

In an embodiment, the inlet is tangential with respect to an inner surface of a wall of the upper flow director.

In an embodiment, the inlet is arranged to direct the driving liquid peripherally into the upper flow director at or near an upper end of the upper flow director.

In an embodiment, the lower flow director is positioned to be at least partly submerged in a body of liquid.

In an embodiment, the apparatus is configured such that, in use, the second spiralling flow is induced in the body of liquid. Preferably at least a portion of the second spiralling flow is below the lower flow director.

In an embodiment, the apparatus has a chamber for holding a body of liquid, with the lower flow director positioned in the chamber. Preferably the lower end of the lower flow director is arranged to be submerged in the body of liquid.

In an embodiment, the chamber comprises an outlet for discharging liquid from the apparatus, the outlet being positioned above the lower end of the lower fluid director. The outlet may be tangential to the chamber, aligned with a predetermined circumferential flow direction in the chamber.

In an embodiment, the chamber is vented to atmosphere. In an embodiment, the chamber is formed by a housing of the apparatus. The vent may optionally comprise a valve operable to open and close under predetermined conditions.

In an embodiment, the vacuum port is positioned generally above or at a top of the upper flow director.

In an embodiment, flow through the apparatus is driven by gravity. In an embodiment, the first spiralling flow is in the form of a vortex about a first vortex axis. The first vortex may generate a force vector along the first vortex axis, directed towards the lower end of the upper flow director.

In an embodiment, the second spiralling flow is in the form of a second vortex about a second vortex axis. The second vortex generates a force vector along the second vortex axis, directed towards the upper end of the lower flow director.

In an embodiment, the first vortex axis and the second vortex axis are colinear.

In an embodiment, the apparatus further comprises a flow control device positioned below the lower flow director to define a flow path therebetween. The flow control device may be configured to induce a laminar flow along the flow path defined thereby. In an embodiment, an upper surface of the flow control device is bell-shaped.

The flow control device is suspended from the mouth of the lower flow director and movable relative to the lower flow director, for example towards and away from the lower flow director. Preferably the flow control device is coaxial with the lower flow director.

In a second aspect, the present invention broadly consists in a system having a plurality of apparatuses according to the first aspect, connected in series.

The system may comprise a mechanical pump. The system may be a closed, recirculating system. Alternatively, the system may be an open system and/or may be gravity driven.

In a third aspect, the present invention broadly consists in a method of generating a negative pressure. The method comprises inducing a first spiralling flow in a liquid whereby the liquid flows in a generally inwardly and downwardly spiralling manner about a first spiral axis, and inducing a second spiralling flow, below the first spiralling flow, in a generally inwardly and upwardly spiralling manner about a second spiral axis, and thereby generating a negative pressure at a port generally positioned above the first spiralling flow.

In an embodiment, the step of inducing a second spiral flow comprises inducing the second spiralling flow in the body of liquid.

In an embodiment, the first spiralling flow and the second spiralling flow are co-axial.

In an embodiment, the step of directing a stream of a driving liquid into a upper flow director to create the first spiralling flow.

In an embodiment, the method comprises directing the stream of driving liquid into the upper flow director in a tangential manner at a periphery of the upper flow director.

In an embodiment, the method comprises discharging liquid at a flow rate substantially the same as a flow rate of the stream of driving liquid. In an embodiment, the negative pressure is generated at a vacuum port positioned generally above or at a top of the first spiralling flow.

In an embodiment, flow from the first and second spiralling flows are generated by gravity and/or a driving head.

In an embodiment, the first spiralling flow is in the form of a vortex and the first axis is a first vortex axis. The first vortex may generate a force vector along the first vortex axis, directed towards the lower end of the upper flow director.

In an embodiment, the second spiralling flow is in the form of a second vortex and the second axis is a second vortex axis. The second vortex generates a force vector along the second vortex axis, directed towards the upper end of the lower flow director.

In an embodiment, the liquid is water.

In an embodiment, the flow through the first and lower flow directors is substantially laminar.

The method may utilise the apparatus according to the first aspect.

The term 'comprising' as used in this specification and claims means 'consisting at least in part of. When interpreting statements in this specification and claims that include the term 'comprising', other features besides those prefaced by this term can also be present. Related terms such as 'comprise' and 'comprised' are to be interpreted in a similar manner.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range and any range of rational numbers within that range (for example, 1 to 6, 1.5 to 5.5 and 3.1 to 10). Therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed.

As used herein the term '(s)' following a noun means the plural and/or singular form of that noun. As used herein the term 'and/or' means 'and' or 'or', or where the context allows, both.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a side section view showing one exemplary embodiment apparatus for generating a negative pressure;

Figure 2 is a top view of the apparatus of Figure 1;

Figure 3 is a side elevation view showing an assembly of the upper and lower flow directors of the apparatus of Figure 1;

Figure 4 is a top view of the assembly of Figure 3; Figure 5 is a diagram illustrating fluid flow through the apparatus of Figures 1 and 2;

Figure 6 is a plan section illustrating fluid flow through the apparatus of Figures 1 and 2;

Figure 7 is a diagram of the apparatus of Figures 1 and 2 arranged in a closed system with a mechanical pump, illustrating flow through the system;

Figure 8 is a diagram showing a plurality of the apparatuses of Figures 1 and 2 arranged closed loop with a mechanical pump, illustrating flow through the system;

Figure 9 is a diagram showing a plurality of the apparatuses of Figures 1 and 2 arranged in an open, gravity driven system, illustrating flow through the system;

Figure 10 a side section view showing a flow director assembly for a second exemplary embodiment apparatus; and

Figure 11 is a perspective view of the flow control device of the apparatus of Figure 10.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention will now be described with reference to Figures 1 to 6 which show an exemplary embodiment apparatus 1 for generating a negative pressure. The apparatus 1 utilises the flow of a fluid through the apparatus to generate a negative pressure.

As used herein, the term 'negative pressure' refers to any pressure that is lower than the pressure surrounding the apparatus 1, for example, this may typically be any pressure lower than atmospheric pressure and includes an absolute or partial vacuum. The terms 'upper', 'lower', 'top', bottom', 'side', and similar terms are used to describe the apparatus 1 with reference to the orientation shown in the accompanying drawings and are not intended to be limiting. It will be understood that the orientation of the apparatus 1 and its components may be changed from the orientation shown in the drawings.

The apparatus 1 generally includes a first, upper flow director 3 and a second, lower flow director 5 in fluid communication with the upper flow director 3. An inlet 7 is in fluid communication with the upper flow director 3 and arranged to direct a driving liquid DL into the upper flow director 3. The driving liquid DL then flows from the upper flow director 3 into the lower flow director 5, before eventually exiting the apparatus 1. A vacuum port 9 is provided generally above or at a top of the upper flow director 3. Fluid flow through the apparatus 1 generates a negative pressure at the vacuum port 9.

The shape of the upper flow director 3 and the position and/or configuration of the inlet 7 are selected to induce a first spiralling flow FV (Figure 5) in the upper flow director 3, in which a driving liquid DL flows in a generally downward and inwardly spiralling manner about a first spiral axis Al. This first spiralling flow FV may have the form of a vortex such that a vacuum is created along a spine of the vortex, generally along the first spiral axis Al. In the first spiralling flow, the liquid flows in a generally circular (but spiralling) manner as illustrated in Figure 6. In alternative embodiments the flow may follow a generally elliptical or other flow path, depending on the shape of the upper flow director 3 and the fluid flow characteristics. In the embodiment shown, the upper flow director 3 is a hollow member with a circular cross section, narrowing from a wide top end 3b to a narrow lower end 3c. That is, the transverse or horizontal cross- sectional area of the upper flow director 3 is largest at or near the top 3b of the upper flow director 3 and reduces along the first spiral axis A1 to be narrowest at or near the base 3c of the upper flow director 3. In the embodiment shown, the upper flow director 3 is shapes as a straight sided funnel, with the main wall 3a of the upper flow director 3 being frustoconical. The main wall 3a tapers in a linear manner, from a wide inlet end 3b to a narrow outlet end 3c, with its radius 3 decreasing linearly along the first spiral axis Al.

In alternative embodiments, the cross-sectional profile of the main wall 3a of the upper flow director may instead be curved, with at least a portion of the inner surface of the main wall 3a being convex or concave such that the radius of the upper flow director decreases non-linearly along spiral axis Al towards the outlet 3c of the upper flow director. In some embodiments, the main wall 3a of the upper flow director may have a concave portion and a convex portion.

The inlet 7 is arranged to direct a stream of liquid tangentially into the upper flow director 3. The inlet 7 is through a wall of the upper flow director 3 and directs a stream of liquid along a flow line at a tangent to the inner surface of the upper flow director immediately adjacent the inlet 7. The flow DL is directed to a periphery of the upper flow director 3, such that it is along the wall of the upper flow director and the inward curve of the flow director wall directs the flow centripetally in a generally circular manner. The inlet 7 typically comprises a hollow member such as a cylindrical pipe or conduit having a flow axis. That is tangential to the inner surface of the wall of the upper flow director at the inlet point.

The inlet 7 is provided at or near the top of the upper flow director 3 and flow through the inlet is typically perpendicular to the first spiral axis Al. In the orientation shown in the Figures, flow through the inlet 7 is substantially horizontal and the first spiral axis Al is vertical. In alternative embodiments, flow through the inlet 7 may be at an angle to horizontal.

A containment cap 10 or sealed lid is provided over a top of the upper flow director 3. The vacuum port 9 comprises an aperture through this cap or lid 10 and may include an upwardly or downwardly projecting member such as a section of pipe or a boss that extends up from or into the cap or lid 10. The projecting member facilitates the connection of the vacuum port 9 to an external component such as a conduit, for coupling the negative pressure to an environment. The projecting member may have external (or internal) features such as ribbing or a thread to facilitate coupling to said external component.

In the embodiment shown, the vacuum port 9 comprises a circular aperture positioned near the centre of containment cap 10, aligned with the first spiral axis Al. However, in alternative embodiments, the vacuum port 9 may be otherwise positioned on the containment cap 10 or in the upper flow director 3. The vacuum port 9 is preferably positioned above the inlet or otherwise positioned such that the driving liquid DL does not pass over the port 9 and so cannot block the vacuum port 9 or exit the apparatus 1 through the port.

Optionally, the vacuum port 9 may comprise a valve to enable the port to be selectively fully or partially open or closed. The lower end 3c of the upper flow director 3 defines an outlet 3c that is in fluid communication with the lower flow director 5, to direct flow into the lower flow director 5 and forming a 'throat 11 of the apparatus 1. In the embodiment shown, the outlet 3c of the upper flow director 3 forms the inlet 5b of the lower flow director 5 and the inner surface of the upper flow director 3 is contiguous with the inner surface of the lower director 5.

The lower flow director is shaped to induce a second spiralling flow SV (Figure 5), in a generally inwardly and upwardly spiralling manner about a second spiral axis A2. In the embodiment shown, the lower flow director 5 is a hollow member with a circular cross section, that generally widens from a narrow top end 5b to a wide lower mouth 5c. That is, the transverse or horizontal cross-sectional area is smallest at or near the top of the lower flow director 5 at the throat and increases along the second spiral axis A2 to be largest at or near the mouth/base 5c of the lower flow director 5. The upper and lower flow directors 3, 5 are arranged to be co-axial.

In the embodiment shown, the lower flow director 5 is generally shaped as an inverted 'trumpet-shaped' funnel with outwardly flaring walls. The cross-sectional profile of the main wall 5a of the lower flow director 5 is curved with a convex inner surface. The radius of the main wall 5a increases in a non-linear manner, from a narrow inlet end 5b to a wide outlet mouth 5c, with the rate of change in the radius increasing with increasing distance from the throat 11.

The curvature of the outwardly flaring wall 5a may be any suitable curve and is selected to give the desired flow characteristics and pressure drop, as discussed in further detail below. For example, the wall may have the curve of a hyperbola. To maximise the size of the negative pressure generated by the apparatus, the curve of the wall 5a is preferably selected to produce a maximum drop in the flow velocity of the driving fluid, without inducing undue turbulence in the flow. In alternative embodiments where lower negative pressures are acceptable, the sides of the lower flow director 5 may instead be straight, in the shape of an inverted straight sided funnel. That is, with the main wall 5a of the lower flow director 5 being frustoconical, tapering in a linear manner with its radius increasing in a linear manner along the second spiral axis A2.

In the embodiment shown, neither the upper or lower flow director 3, 5 comprises any internal baffles, flow guides, axial flow directors, or veins. However, in alternative embodiments, one of more of those features may be used on one or both of the flow directors to guide or better utilise the driving fluid. Further, the inner surfaces of one or both of the flow directors 3, 5 may be engineered, such as by selecting the surface roughness, to help to generate the desired flow characteristics.

Figures 10 and 11 show a second embodiment flow director assembly 101 in which, unless otherwise described, like reference numerals are used to indicate like parts but with the addition of 100. The flow director assembly 101 is shown independent of any housing, but it is to be understood that the mouth of the lower flow director 105 will be submerged in a body of water as described above and the assembly 101 may be used with the housing described above in relation to the first embodiment 1.

In this embodiment flow director assembly 101, a flow control device 125 is installed beneath the outlet mouth 5c of the lower flow director 5. The flow control device 125 is a bell-shaped component positioned below the lower flow director 105 such that fluid flowing out of the mouth of the lower flow director 105 flows along a flow path defined by the mouth 105c of the lower flow director and the upper surface of the flow control device 125.

The upper surface of the flow control device 125 shown is a bell-shaped with a circular perimeter, a generally concave curvature around an annular portion thereof, and with a raised central portion 125a of convex curvature at its apex. The annular portion sits directly below and coaxially with the lower flow director 105. The curvature of the concave annular portion of the flow control device 125 may have a curvature that follows the curvature of the lower flow director 105c, such that the spacing between the two components 105, 125 is substantially constant along the flow path defined therebetween. In alternative embodiments, the curvature may be such that the spacing between the two components 105, 125 converges or diverges along the flow path defined therebetween. In alternative embodiments, the flow control device 125 may have an alternative shape, for example the apex of the central portion 125a could be pointed.

In the embodiment shown, a plurality of bolts or protrusions 127 are provided spaced around the perimeter of the flow control device 125, extending up from the flow director 125. The bolts or protrusions 127 are centred on a diameter that corresponds to or is slightly larger than the outer diameter of the mouth 105c of the lower flow director 105. To assemble the flow control device 125 with the lower flow director 105, the bolts are installed with the head of the bolt or an enlarged head or the protrusion 127 resting on the lower flow director 105 at its periphery. In this manner the flow control device 125 is suspended from the lower flow director 105. In use, the flow control device 125 is free to move upwards towards the lower flow director 105 depending on the net forces acting on the flow control device due to induced vacuum and exiting fluid pressure positioned centrally beneath exit cone 5. Downwards movement of the flow control device 125 is limited by the length of the bolts or protrusions 127.

In alternative embodiments, the flow control device 125 may be otherwise attached to the lower flow director 105. For example, the bolts 127 may extend through apertures in the lower flow director 105, or flexible tensile members or other suitable connectors may be used in place of the bolts 127. In the embodiment shown four bolts 127 are provided to suspend the flow control device 125 from the lower flow director 105, but alternatively more or fewer connectors may be provided. For example, two, three, five, six, or more connectors. In alternative embodiments, the flow control device may be fixed relative to the lower flow director such that the spacing between the components is fixed in use and the flow control device is unable to freely move up and down relative to the lower flow director 105. In such embodiments, the spacing between the components may be adjustable to regulate or direct the flow as desired. In a further alternative embodiment, the flow control device may be arranged asymmetrically, for example hinged at one side such that the spacing with the lower flow director 105 varies around the annular portion of the flow control device 125.

The intensity of the vacuum produced by the apparatus 1, 101 (not shown in full) has been shown in testing to at least in part be correlated with the extent of the laminar flow across the surface of the lower flow director 5, 105. The inclusion of the flow control device 125 may increase the extent of the laminar flow across the surface of the lower flow director at the mouth 105c of the flow director and may ensure that laminar flow is maintained across the entire lower surface of the mouth of the flow director 105. In testing a vacuum of over 95% was achieved with this embodiment.

In use, the lower flow director 5 is at least partly submerged in a body of liquid, with at least the mouth 5c of the lower flow director 5 being submerged. The body of liquid may be provided by a reservoir that is external to the apparatus, such as a natural body of water or a pool into which the apparatus is placed. Figure 9 illustrates one embodiment system utilising an external body of water. Alternatively, the body of liquid may be contained by a chamber 13 within the apparatus 1.

In the embodiment shown, a housing 15 houses the upper and lower flow directors 3, 5, and also forms a chamber 13 for holding a body of liquid. The lower end 5c of the lower flow director 5 is positioned in the chamber, arranged to be submerged in the body of liquid. The dimensions of chamber 13 are selected to allow liquid flowing out of the lower flow director 5 to flow between the lower flow director 5 and the wall of the chamber 13. The chamber 13 is also shaped such that in use, the second spiralling flow SV is induced in the body of liquid in the chamber, generally below the lower flow director 5.

In alternative embodiments to the one shown, the chamber 13 may include baffles, flow guides, or veins to guide liquid in the chamber. Alternatively or additionally, features of the inner surface(s) of the housing, such as surface roughness, may be selected to provided desired flow characteristics. The housing may have any suitable shape and shapes other than that shown in the accompanying Figures are anticipated. For example, the housing may be substantially cylindrical.

The chamber 13 may be open or vented to atmosphere. In the exemplary embodiment shown, the housing 15 has a vent 17 that opens to the environment surrounding the apparatus 1. The surrounding environment is typically at atmospheric pressure, so that an upper surface of the body of liquid will also be at atmospheric pressure. The vent 17 is positioned higher than the liquid level or head of the chamber 13. Optionally, the vent 17 may comprise a valve to selectively open and close the opening depending on conditions in the apparatus. In one alternative embodiment, the valve comprises a valve operated by a double acting float switch that is configured to close when the liquid level in the chamber reaches a predetermined height, and open once the liquid level in the chamber has dropped down to a second lower predetermined height.

The chamber 13 has an outlet 19 for discharging liquid from the apparatus 1. The outlet 19 is positioned at a discharge height that is higher than the mouth 5c of the lower fluid director 5, but lower than the inlet 7. In some embodiments, the outlet height is in line with or below the lower end of the upper flow director 3.

The outlet 19 typically comprises a cylindrical pipe. The pipe may have the same or a similar diameter to that of the inlet pipe 7 such that the flow rate and velocity of fluid flow DL into the apparatus 1 is the same as the flow rate and velocity of fluid flow out of the apparatus outlet 19. Referring to Figure 2, the outlet 19 may be arranged tangentially relative to the flow direction in the fluid chamber 13, that is, aligned with the tangential component of the flow vector in the fluid chamber. In the embodiment shown, the apparatus is configured such that the direction that rotational direction of fluid flow in the transverse plane is the same in the upper flow director 3 and the fluid chamber 15. The apparatus 1 may be constructed from any suitable material, for example but not limited to, one or more of a metal such as a steel alloy, a plastic material, or a composite material. The apparatus 1 may be formed as a single unit or may be formed from two or more components assembled using any suitable method as will be apparent to those skilled in the art.

Use of the apparatus and fluid flow in the apparatus will now be described with reference to Figure 5. A stream of a driving liquid DL flows through the inlet 7, into the upper flow director 3. The driving liquid is typically water; however, the use of other liquids is anticipated without altering the functionality of the apparatus. The fluid flow through the apparatus is driven by a drop in the water head between the inlet and the outlet (the change in head being the 'driving head'). The apparatus 1 may be gravity driven with the driving head provided by one or both of an elevated fluid source fluidly coupled to the inlet 7, and/or the outlet 19 being fluidly coupled to discharge fluid at a lower height than the air vent 17.

Alternatively, the driving head may be provided by a mechanical pump 25 delivering the stream of liquid to the inlet 7. Figure 7 illustrates an embodiment in which liquid from the apparatus outlet 19 is drawn along an outlet pipe 21 into a pump 25, and recirculated by pumping the liquid back to the inlet 7. In such a system, a plurality of apparatuses 1, 1', 1" may be connected in series, as illustrated in the exemplary system of Figure 8.

The driving liquid DL entering the upper flow director 3 moves in a downwardly and inwardly spiralling manner, around the circumference of the upper flow director 3. Flow through the upper flow director 3 comprises tangential, radial, and downwards flow components.

The first spiralling flow FV forms a vortex about the first spiral axis Al, generating a vacuum along the spiral axis Al and thereby a force vector along the first vortex axis, directed towards the lower end 3c of the upper flow director. This downward force draws gases through the open vacuum port 9, into the upper flow director 3.

The flow of the driving liquid DL accelerates as it is drawn into the lower pressure area or vacuum as it approaches the outlet 3c of the upper flow director 3, as the diameter of the flow director 3 reduces towards its narrowest point. As the flow passes through the narrowest point at the throat 11 at the outlet 3c of the upper flow director and inlet 5b of the lower flow director, the motion of the driving liquid has transitioned to be substantially axial due to the increased velocity of the liquid, aligned with the first and second spiral axes Al, A2. Preferably the flow of the driving liquid DL through the upper flow director 3 remains substantially laminar.

The driving fluid then enters the lower flow director 5 through its inlet 5b the fluid is at its fastest velocity at this point, being point of the apparatus with the narrowest cross-sectional area. The fluid then flows in a generally downward and outwardly winding manner, generally circumferentially along the diverging wall 5a of the lower flow director, being drawn across the mouth 5c of the lower flow director 5. The mouth 5c of the lower flow director has a larger cross-sectional area relative to that of the throat 5b, adhesion of the laminar flow of the driving liquid to the inner surface of the lower flow director 5 incites a vacuum in the low-pressure zone beneath the lower director 5. Preferably the flow of the driving liquid DL through the lower flow director 5 remains substantially laminar. Flow out of the lower flow director 5 then generally continues along a trajectory continuing from the wall curvature of the lower flow director, creating a circulating flow in the body of liquid as illustrated by the streamlines CF in Figure 5.

The effect of the diverging flow through the lower flow director 5 is to induce a second spiralling flow SV, spiralling in a generally inwardly and upwardly about a second spiral axis A2. The second spiralling flow SV is formed in the body of liquid that the lower flow director 5 is submerged in. At least a portion of the second spiralling flow SV is located below the mouth 5c of the lower flow director 5. An upper portion of the spiralling flow may extend up into the lower flow director 5, as illustrated in Figure 5.

The second spiralling flow SV preferably forms of a second vortex about the second spiral axis A2, generating a vacuum along the second spiral axis A2 and thereby a force vector along the second spiral axis A2, directed towards the upper end of the lower flow director 5. This force vector counteracts the force vector A1 to maintain the balance of the vacuum within the system. The flow pattern created by the resulting vacuum draws liquid away from the wall of the respective flow director in a generally elliptical orbit around the spine of the vacuum, resulting in reduced friction between the wall and the liquid.

The axes Al, A2 of the first and second vortexes are colinear and the first and second spiralling flows FV, SV together form a bi-polar vortex structure.

Gases that are drawn through the open vacuum port 9 into the upper flow director 3 are drawn through the upper and lower flow directors, becoming entangled within the flow of the driving liquid DL, and entering the body of liquid in the chamber 13. The gasses rise after exiting the mouth 5c of the lower flow director 5, and are vented to out of the apparatus via the vent 17 in the housing.

Finally, the driving liquid DL is discharged from the apparatus 1 via the outlet 19. Preferably the liquid is discharged continuously, at a flow rate substantially the same as a flow rate of the driving liquid DL through the inlet 7.

Preferably both the inlet 7 and outlet 9 are kept under a liquid lock, for example by keeping them submerged, to maintain a sealed environment within the apparatus, preventing the ingress of gasses through any port other than the vacuum port 9.

Fluid is able to flow through the apparatus whether the vacuum port 9 is open for applying a negative pressure, or closed. Example embodiment

In one example embodiment as shown, the relative dimensions of the components and the resulting performance characteristics are as follows:

In some applications, a plurality of apparatuses 1, 1', 1" according to the present invention may be connected in series to produce a larger negative pressure for higher volume applications. In such an embodiment, the outlet 19, 19' of an upstream apparatus 1, 1' would be arranged to feed into the inlet 7', 7" of a downstream apparatus 1', 1". The system may be a closed system such as the one illustrated in Figure 8 whereby the driving liquid is circulated by way of a mechanical pump. Alternatively, the system may be open and gravity driven, for example such as the system of Figure 19, with a system input comprising a reservoir 31.

Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention.

Claims

1. An apparatus for generating a negative pressure, comprising: an upper flow director; an inlet for directing a driving liquid into the upper flow director; a lower flow director in fluid communication with the upper flow director; and a vacuum port; wherein the upper flow director is shaped to induce a first spiralling flow in which the driving liquid flows in a generally inwardly and downwardly spiralling manner about a first spiral axis; and wherein the lower flow director is shaped to induce a second spiralling flow in a generally inwardly and upwardly spiralling manner about a second spiral axis; and wherein flow of the driving liquid through the apparatus generates a negative pressure at the vacuum port.

2. An apparatus as claimed in claim 1, wherein the upper flow director generally narrows from a wider inlet end to a narrow outlet end.

3. An apparatus as claimed in claim 2, wherein the upper flow director is shaped as a funnel.

4. An apparatus as claimed in claim 2, wherein a tapering wall of the upper flow director is substantially straight.

5. An apparatus as claimed in claim 2 or 3, wherein a tapering wall of the upper flow director is curved.

6. An apparatus as claimed in any preceding claim, wherein the lower flow director generally widens from a narrow inlet end to a wider outlet end.

7. An apparatus as claimed in claim 6, wherein the lower flow director is shaped as an inverted funnel.

8. An apparatus as claimed in claim 6 or 7, wherein a wall of the lower flow director has a curved profile.

9. An apparatus as claimed in claim 8, wherein said curved wall of the lower flow has a convex inner surface.

10. An apparatus as claimed in claim 8 or 9, wherein said curved wall of the lower flow has the curve of a hyperbola.

11. An apparatus as claimed in any preceding claim, wherein the upper flow director has an outlet that is coincident and/or coaxial with an inlet for the lower flow director.

12. An apparatus as claimed in any preceding claim, wherein the inlet is tangential with respect to an inner surface of a wall of the upper flow director.

13. An apparatus as claimed in any preceding claim, wherein the inlet is arranged to direct the driving liquid peripherally into the upper flow director at or near an upper end of the upper flow director.

14. An apparatus as claimed in any preceding claim, wherein the lower flow director is positioned to be at least partly submerged in a body of liquid.

15. An apparatus as claimed in claim 14, wherein the apparatus is configured such that, in use, the second spiralling flow is induced in the body of liquid.

16. An apparatus as claimed in claim 15, wherein at least a portion of the second spiralling flow is below the lower flow director.

17. An apparatus as claimed in any preceding claim, comprising a chamber for holding a body of liquid, with the lower flow director positioned in the chamber.

18. An apparatus as claimed in claim 17, wherein the lower end of the lower flow director is arranged to be submerged in the body of liquid.

19. An apparatus as claimed in claim 17 or 18, wherein the chamber comprises an outlet for discharging liquid from the apparatus, the outlet being positioned above the lower end of the lower fluid director.

20. An apparatus as claimed in claim 19, wherein the outlet is tangential to the chamber, aligned with a predetermined circumferential flow direction in the chamber.

21. An apparatus as claimed in any one of claims 17 to 19, wherein the chamber is vented to atmosphere.

22. An apparatus as claimed in any preceding claim, wherein the vacuum port is positioned generally above or at a top of the upper flow director.

23. An apparatus as claimed in any preceding claim, wherein flow through the apparatus is driven by gravity.

24. An apparatus as claimed in any preceding claim wherein the first spiralling flow is in the form of a vortex about a first vortex axis.

25. An apparatus as claimed in claim 24, wherein the first vortex generates a force vector along the first vortex axis, directed towards the lower end of the upper flow director.

26. An apparatus as claimed in claim 24 or 25, wherein the second spiralling flow is in the form of a second vortex about a second vortex axis.

27. An apparatus as claimed in claim 26, wherein the second vortex generates a force vector along the second vortex axis, directed towards the upper end of the lower flow director.

28. An apparatus as claimed in claim 26 or 27, wherein the first vortex axis and the second vortex axis are colinear.

29. An apparatus as claimed in any preceding claim, further comprising a flow control device positioned below the lower flow director to define a flow path therebetween.

30. An apparatus as claimed in claim 29, wherein the flow control device is configured to induce a laminar flow along the flow path defined thereby.

31. An apparatus as claimed in claim 29 or 30, wherein an upper surface of the flow control device is bell-shaped.

32. An apparatus as claimed in any one of claims 29 to 31, wherein the flow control device is suspended from the mouth of the lower flow director and movable relative to the lower flow director.

33. A system comprising a plurality of apparatuses as claimed in any preceding claim, connected in series.

34. A system as claimed in claim 33, wherein the system comprises a mechanical pump.

35. A method of generating a negative pressure, comprising: inducing a first spiralling flow in a liquid whereby the liquid flows in a generally inwardly and downwardly spiralling manner about a first spiral axis; and inducing a second spiralling flow, below the first spiralling flow, in a generally inwardly and upwardly spiralling manner about a second spiral axis; and thereby generating a negative pressure at a port generally positioned above the first spiralling flow.

36. A method as claimed in claim 35, wherein the step of inducing a second spiral flow comprises inducing the second spiralling flow in the body of liquid.

37. A method as claimed in claim 35 or 36, wherein the first spiralling flow and the second spiralling flow are co-axial.

38. A method as claimed in any one of claims 35 to 37, comprising directing a stream of a driving liquid into a upper flow director to create the first spiralling flow.

39. A method as claimed in any claim 38, comprising directing the stream of driving liquid into the upper flow director in a tangential manner at a periphery of the upper flow director.

40. A method as claimed in claim 38 or 39, comprising discharging liquid at a flow rate substantially the same as a flow rate of the stream of driving liquid.

41. A method as claimed in any one of claims 35 to 40, wherein the negative pressure is generated at a vacuum port positioned generally above or at a top of the first spiralling flow.

42. A method as claimed in any one of claims 35 to 41, wherein flow from the first and second spiralling flows are generated by gravity and/or a driving head.

43. A method as claimed in any one of claims 35 to 42, wherein the first spiralling flow is in the form of a vortex and the first axis is a first vortex axis.

44. A method as claimed in claim 43, wherein the first vortex generates a force vector along the first vortex axis, directed towards the lower end of the upper flow director.

45. A method as claimed in claim 43 or 44, wherein the second spiralling flow is in the form of a second vortex and the second axis is a second vortex axis.

46. A method as claimed in claim 45, wherein the second vortex generates a force vector along the second vortex axis, directed towards the upper end of the lower flow director.

47. A method as claimed in any one of claims 35 to 46, wherein the liquid is water.

48. A method as claimed in any one of claims 35 to 47, utilising the apparatus of any one of claims 1 to 32.

49. A method as claimed in claim 48, wherein the flow through the first and lower flow directors is substantially laminar.

50. A method as claimed in any one of claims 35 to 47, utilising the apparatus of any one of claims 29 to 32, wherein flow between surfaces of the flow control device and the lower flow director is substantially laminar.