FIELD OF THE INVENTION

The invention relates to the field of pumps and methods of pumping fluids.

BACKGROUND

Positive displacement pumps provide moving pumping chambers for moving a fluid between a fluid inlet and a fluid outlet. The pumping chambers are in general formed between one or more rotors and a pumping housing in which the rotors are mounted. Such pumps include roots and rotary vane pumps.

In order to reduce leakage and move the gas efficiently while it is trapped the moving parts need to form a close seal with each other and with the static parts which form the trapped volume of gas. Some pumps may use a liquid such as oil to seal between the surfaces of the trapped volume whilst others rely on tight non-contacting clearances which can lead to increased manufacturing costs and can also lead to pumps that are sensitive to locking or seizure if the parts come into contact or where particulates or impurities are present in the fluid being pumped.

One alternative to having solid surfaces that need to form a close seal is a liquid ring pump. The blades of a liquid ring pump create volumes which are sealed from each other either by a liquid ring lining the circumference of the stator bore. This reduces the requirement for high manufacturing tolerances, and provides a pump with low wear as the rotor blades do not contact the stator bore. However, a drawback is that this type of pump typically has a high power consumption and operates at low frequency to reduce drag losses, turbulence and cavitation.

All of these types of pump have bearings to support and allow rotation of the shaft/rotor and are generally driven by an electric motor with additional bearings. These bearings add to the manufacturing costs of the pump and suffer from wear. It would be desirable to provide a pump that is resistant to wear, offers low power consumption and relatively small pumping mechanism and is relatively cheap to manufacture and operate.

SUMMARY

A first aspect provides a pump for pumping a fluid comprising: a pump housing comprising a fluid inlet and a fluid outlet; a core mounted within said pump housing; a liquid with magnetic properties confined within said pump housing; a rotating magnetic field generating means configured to generate a rotating magnetic field within said pump housing, said rotating magnetic field comprising a plurality of rotating magnetic poles each operable to drive said magnetic liquid, such that said magnetic liquid is caused to rotate in response to said rotating magnetic field and to drive said fluid from said fluid inlet to said fluid outlet.

The use of rotating solid surfaces to entrap a fluid in a pumping chamber and drive the entrapped fluid through a pump is an effective solution for pumping but has drawbacks related to the sealing between solid surfaces required to form pumping chambers. This has been addressed to some extent by the use of lubricants in conventional rotary vane pumps and by a liquid ring pump. Each of these pumps however, requires bearings to mount the rotating solid surfaces and these present their own problems for manufacturing costs and servicing requirements. The inventors of the present invention have provided an elegant alternative solution to this problem where the driving force is provided not by a solid surface but by a magnetic liquid which is itself driven by a rotating magnetic field. In this way a simple, compact, low power, low cost mechanism for driving a fluid through a pump is provided, where the problems that arise due to friction and wear between contacting surfaces and the cost involved in manufacturing tolerances for tight clearances are avoided or at least mitigated. The use of magnetic liquids and a rotating magnetic field to provide such a driving force, provides a simple and yet robust pump. Furthermore, the cost and maintenance associated with mounting rotating parts is reduced if not completely removed.

In some embodiments, said rotating magnetic field generating means is mounted around said pump housing.

One way of providing a rotating magnetic field within a pump housing is to mount the rotating magnetic field generating means around the pump housing. In this regard, the cross-section of the pump housing may have different shapes but in some embodiments it may be circular.

In some embodiments, said rotating magnetic field generating means comprises a component equivalent to a stator of an electric motor. The generation of rotating magnetic fields is a well known problem in electric motors that people have spent much time and effort addressing. Thus, the rotating magnetic field generating means can be effectively and relatively cheaply provided by using a component configured in the same way that a stator of an electric motor is configured. The pump housing can be mounted within such an electric motor stator such that the rotating magnetic field generating means is around the pump housing and provides a rotating magnetic field within it.

In some embodiments, said rotating magnetic field generating means comprises a plurality of windings or coils each configured to be connected either to an alternating current power supply or a switched DC power supply, such that each winding is driven by an electric current that has a phase difference with respect to the current driving neighbouring windings.

One way of generating a rotating magnetic field that does not require moving parts, such that it can be cheaply and efficiently manufactured and have low servicing requirements, is by the use of windings that are connected to an alternating current or switched DC power supply that provides neighbouring windings with electric current which is out of phase with each other. With the switched DC supply the phase difference arises due to a difference in direction of the current through the windings. In some embodiments, the pump comprises control circuitry for controlling power supplied to said rotating magnetic field generating means..

By suitable control of the power supply, the windings each provide a magnetic field that varies over time, and a magnetic pole generated by one winding will in a subsequent time interval be generated by a subsequent winding. In this way the magnetic pole in effect moves from winding to winding as the phase of the input signal changes, providing a rotating magnetic field without the requirement for moving parts and their associated bearings, in a corresponding way to the way a stator of an electric motor provides a rotating magnetic field.

In alternative embodiments, said rotating magnetic field generating means comprises a plurality of permanent magnets mounted to rotate during operation.

An alternative way of generating the rotating magnetic field is to rotatably mount permanent magnets such that they can be driven to rotate. This does require bearings and moving parts and thus may be less advantageous than the previous embodiment.

The core may be mounted centrally within the pump housing. However, in some embodiments, the core is mounted offset to a centre of said pump housing, such that a distance between said core and said pump housing changes around a perimeter of said core.

Mounting the core offset to the centre of the pump housing means that when fluid is driven around the core by the rotating magnetic liquid, the pocket of gas that is entrapped by the magnetic liquid will change in volume as the magnetic liquid rotates. This provides compression and expansion of the gas entrapped, allowing fluid to be sucked into the pump housing at the inlet located on an end face of the pump housing at a perimeter point where the core is more remote from the pump housing and expelled from it at the outlet located on the pump housing at a perimeter point where the core is closer to the pump housing.

In alternative embodiments where the core is mounted centrally within the pump housing, then some sort of blocking mechanism is required after the outlet in the direction of rotation, such that as the magnetic liquid rotates, any entrapped fluid is pushed out of the outlet by the rotating magnetic liquid and the blocking mechanism located after the outlet. This blocking mechanism or obstruction may itself be formed of the magnetic liquid held in place perhaps by a permanent magnet.

In some embodiments, said plurality of windings are mounted on said core.

As an alternative or addition to the plurality of windings being mounted around the pump housing, in some embodiments they are mounted on the core. This has the advantage of any magnetic field generated by these windings being more easily contained within the pump housing and thereby having a lesser effect on components outside of the housing.

In some embodiments, said rotating magnetic field generating means comprises a plurality of further windings mounted on said core, said plurality of further windings corresponding to said plurality of windings mounted on said pump housing, said plurality of windings and further windings being configured to connect to an alternating current or switched DC power supply such that windings on said pump housing and said further windings on said core generate rotating magnetic fields of opposing poles that rotate in synchronisation with each other. In some cases there may be windings on both the core and around the edge of the pump housing. Advantageously, these are configured to be supplied with an alternating current or switched DC power supply that is synchronised, such that opposing poles rotate in synchronisation with each other providing an increased magnetic field between the core and the pump housing. This increased magnetic field enables the magnetic liquid held between the two poles to form a more robust blade and therefore withstand higher pressure differentials between the pumping chambers that the blades define.

In some embodiments, corresponding windings on said core and said pump housing are formed of a same winding. One way of providing synchronised supply is to form the corresponding windings as a same winding, in effect two coils formed from a single wire. As the coils are directly connected to each other, then the pair of coils are energised in phase with each other and there is no need to separately synchronise the power supplied to them.

In some embodiments, said core is formed of one of a polymer or a ceramic.

In order to reduce eddy currents and associated heating and power losses, it may be advantageous if the core is formed of a non-conductive material and a polymer or a ceramic has been found to be particularly advantageous.

In other embodiments, where the windings are mounted on the core, then it may be advantageous if the core if formed of iron. In some embodiments, said pump is configured such that in response to said rotating magnetic field said plurality of rotating poles each attract said magnetic liquid, such that a plurality of rotating blades formed of said magnetic liquid and corresponding to said plurality of rotating poles are formed to drive said fluid. The rotating magnetic field is formed of a plurality of rotating poles each of which attracts magnetic liquid such that each pole has a corresponding blade formed of the magnetic liquid associated with it. Thus, increasing the number of poles increases the number of blades and pumps can be designed according to their required properties in this way.

In some embodiments and in particular in embodiments where there is no core within the pump housing, said rotating magnetic field generating means and pump housing may be configured such that they are not concentric with each other.

This may be achieved in some embodiments by said rotating magnetic field generating means being mounted around said pump housing such that it is offset from a centre of said pump housing.

In other embodiments, the pump comprises a sleeve mounted within said pump housing offset from a centre of said pump housing, said sleeve forming at least a portion of a perimeter of a working pump chamber.

Where the rotating magnetic field generating means and working pump chamber are not concentric with each other, then the gas that is entrapped by the rotating magnetic liquid will change in volume as the magnetic liquid rotates. This provides compression and expansion of the entrapped gas.

In some embodiments, said pump is configured such that in response to said rotating magnetic field said plurality of rotating poles each attract said magnetic liquid, such that a plurality of rotating blades and a rotating core is formed of said magnetic liquid, wherein said offset of said working pump chamber with respect to said rotating magnetic field generating means is such that said rotating core moves towards and away from a surface of said working pump chamber as it rotates. Providing the rotating magnetic field generating means offset from the centre of the working pump chamber allows the magnetic liquid to be preferentially positioned to one side of the pump housing. Where the magnetic liquid forms both a core of a rotor and the blades, then having it held offset from the centre of the pump housing provides changing volumes of the pumping chambers as they rotate, allowing expansion and compression of the pumped gas which makes for effective pumping operation.

In some embodiments, said rotating magnetic field generating means is configured to generate at least four rotating magnetic poles. Although the rotating magnetic field generating means may only generate two rotating magnetic poles, generally it is advantageous if there are at least four rotating magnetic poles as two will simply provide two blades extending from the core providing two pumping chambers, which may not provide a particularly effective pumping operation. At least four provides four pumping chambers between the four blades and can provide a more effective pump.

In some embodiments, said pump housing is formed of one of a ceramic and a polymer. Providing the pump housing of a ceramic or a polymer leads to a non-conductive pump housing which is advantageous as it reduces eddy current and therefore power losses. In effect, any non-conductive material may be used to form the pump housing but ceramics and polymers have been found to be effective. Polymers in particular can be formed using 3D printing which can make it a particularly cost effective way of manufacturing the device.

In some embodiments, said pump comprises a plurality of stages, said fluid output through said fluid outlet in a first stage being input to a fluid inlet in a subsequent stage. Although the pump may be a single stage pump, it may be advantageous to have multiple stages with the increased pressure differential between an inlet and outlet that this allows. In some embodiments, said magnetic liquid comprises one of a ferrofluidic liquid, an ionic liquid with magnetic properties and magnetic rheological fluid.

The magnetic liquid may be formed of a number of different liquids, for example, a ferrofluidic liquid, an ionic liquid with magnetic properties or a magnetic rheological fluid. In this regard, an ionic liquid may be particularly advantageous as they are generally relatively inexpensive and have low vapour pressures which can be particularly advantageous in a vacuum pump. An example of an ionic liquid with magnetic properties is 1 -butyl-3-methylimidazolium tetrachloroferrate. In some embodiments, said pump comprises a rotary vane pump, said vanes being formed by said magnetic liquid under the effect of said rotating magnetic field generated by said rotating magnetic field generating means.

Although the magnetic liquid can be used to pump liquids in a number of ways, in some embodiments it forms a rotary vane pump, the vanes being formed by the magnetic liquid. Forming vanes from a magnetic liquid provides vanes that are deformable and allows for the changing volumes of the pumping chambers as they rotate without any requirement for mechanical means to change their lengths.

A second aspect of the present invention provides a method of pumping a fluid comprising: forming a rotating magnetic field comprising multiple poles within a pumping housing containing a core and a liquid with magnetic properties; and driving said fluid from a fluid inlet to a fluid outlet in response to said magnetic liquid rotating within said rotating magnetic field. ln some embodiments, the method comprises an initial step of forming blades from said magnetic liquid by generating a rotating magnetic field rotating at a high speed to cause said magnetic liquid to rotate; and slowing down said rotating magnetic field such that said rotating magnetic liquid coalesces to form a plurality of blades corresponding to said plurality of poles.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 illustrates a cross section through an 8 pole rotary vane pump according to an embodiment;

Figure 2 illustrates a cross section through a 4 pole rotary vane pump according to an embodiment;

Figure 3 illustrates a cross section through a rotary vane pump with no solid core according to a related technique;

Figure 4 illustrates a cross section through a 4 pole rotary vane pump having windings on the core and stator according to an embodiment;

Figure 5 illustrates a longitudinal section through a single stage pump of any one of Figures 1 to 2; and

Figure 6 illustrates a longitudinal section through a multiple stage pump of any one of Figures 1 to 2. DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. A pump and in preferred embodiments a rotary vane pump is provided wherein the fluid is driven through the pump from an inlet to an outlet by a magnetic liquid itself driven by a rotating magnetic field. The magnetic liquid forms the blades of the rotary vane pump, which blades rotate in response to the rotating magnetic field. The rotating magnetic field can be generated by different means, but in some embodiments it is generated using windings that are supplied by AC or switched DC current that is out of phase with the current supplied to neighbouring windings. This is a well-known technique used in many induction motors for generating a rotating magnetic field. In this way rotating blades are formed without the requirement for bearings to mount the rotating parts.

By utilising the magnetic field generated within an induction motor stator, in some embodiments a 3-phase induction motor, blades/vanes can be formed from liquids with magnetic properties such as ferrofluidic liquids, magnetic rheological liquids and some Ionic fluids. These magnetic liquids when placed into the stator bore will be formed into blades/vanes by the magnetic field generated within the motor stator bore. The number of blades will depend on the shape of the magnetic field which in turn is dependent on the number of poles (2, 4, 6, 8) that the motor is wound with. By placing an offset stationary core within the bore of the motor expanding and contracting volumes can be generated as the liquid blades rotate with the rotating magnetic field around the offset stationary core. If this core is constructed from a non-metallic polymer or a ceramic electrical losses will not be incurred in the rotor eliminating or at least reducing heat generation in the core. To constrain the magnetic liquid a concentric polymer sleeve may be placed into the bore of the motor stator to form side surfaces of the pumping chamber, the end faces being formed at each end of the stator core. In this type of construction, no bearings are required for either pump or motor. The only moving part is the magnetic liquid which will rotate at the rotational frequency of the magnetic field. This can be selected by changing the frequency of the electricity supply. An alternative to the offset central core is to mount the magnetic field generating means offset to the pumping chamber, perhaps by providing a sleeve eccentrically in the bore of the motor stator. In this way, the expanding and contracting volumes are formed purely by the magnetic liquid rotating in the eccentric bore and no solid core is required. Ferrofluidic liquids are in some examples oils that comprise micro or nano magnetic particles within them. They are used in dynamic gas seals to make a hermetic seal between rotating shaft components and a stationary casing. The ferrofluidic liquid is held within a magnetic field between the two components and can achieve 200 mbar per fluid ring. They can have a relatively high vapour pressure and can be costly.

Ionic liquids by contrast are generally less expensive and one of their generic characteristics is an extremely low vapour pressure making them ideal for use in vacuum pumps. Magnetic ionic liquids exist in which one or both ions contain magnetic atoms (e.g. iron). A magnetic ionic liquid could be used to create the blades in the above described rotating liquid blade pump and their reduced cost and low vapour pressure may make them preferable to ferrofluids. An alternative liquid that may be used is a magnetic rheological fluid. Figure 1 shows a rotary vane pump according to an embodiment where the vanes are generated using a magnetic liquid 20 suspended in a magnetic field 30. The magnetic liquid 20 may be a ferrofluidic liquid, a magnetic rheological liquid or a magnetic Ionic liquid. The magnetic field 30 is generated in this embodiment by a 3-phase induction motor windings or coils 31 , at 50 Hz frequency and rotating at 1500RPM, but could be any type of motor or any means that generates a rotating magnetic field. Expanding and contracting volume pumping chambers 22 are formed between the rotating liquid blades by placing an offset polymer core 32 within the pump housing. The pump housing in this embodiment comprises a polymer sleeve 35 mounted within the motor stator bore to form a working pump chamber. The outer edges of the rotating volumes defined by the pumping chambers 22 are bounded by the polymer sleeve 35. The ends of the enclosed volumes are sealed by an end face 41 (see Figure 5).

As the magnetic liquid blades rotate with the rotating magnetic field 30, the liquid blades first bound expanding volumes enabling gas to enter through an inlet port 45 (see Figures 3 and 5) placed on the inlet end face, and be trapped. Further rotation will cause the liquid to be squeezed into a reducing gap between the offset core 32 and the concentric sleeve 35 in the bore of the motor. The liquid fills the space pushing gas out of an outlet port 46 (see Figure 3 and 5) placed in the exhaust end face.

In order to generate the blades, the pump may in some embodiments be initially run at a high frequency by using a high frequency input electricity supply, the speed of rotation of the magnetic field could then be slowed by reducing the frequency allowing the magnetic liquid to coalesce and form blades stretching from the core towards the rotating poles.

The magnetic liquid may be a number of things depending on the required properties of the pump. In some embodiments the magnetic liquid is a magnetic ionic liquid and comprises 1 -butyl-3-methylimidazolium tetrachloroferrate.

Three phase motors can be wound in such a way as to generate differing numbers of poles. In Figure 1 there are 8 poles shown, formed by the windings being wound to generate such a configuration. A rotating magnetic field is formed in the same way as that formed by an induction motor stator. Figure 2 shows an alternative embodiment with the 3 phase motor winding is wound to give fewer poles and hence fewer blades or vanes. A pump with increased number of blades has an improved performance. The speed of rotation of the vanes is dependent on the frequency of the electricity supply driving the windings. An increased frequency increases the speed of rotation and thus, the volume of fluid pumped.

Figure 3 shows an alternative technique, where there is no solid core within the pump housing, the core being formed from the magnetic liquid. In such an embodiment in order to get the change in volume of the pumping chambers between the inlet and outlet, the pump housing formed by an eccentric polymer sleeve 35 may be mounted eccentrically within the stator bore, such that as the magnetic liquid rotates it becomes closer to and further from one side of the pumping chamber acting like an eccentrically mounted core. In effect in this embodiment the magnetic liquid rotates concentrically with the stator bore and the bore of the pumping chamber is configured to be closer in one region to the stator bore and thus the liquid core and further away in another region. Inlet 45 and exhaust 46 located on the end faces at different circumferential positions are also shown in this figure.

In Figures 1 to 3 individual coils are formed from one of three windings fed by one of three phases of a three phase power supply. The windings are denoted by letters A, B or C. The different coils of each winding A, B, C are shown by a red or blue dot, the different colours and the + or - sign before the A, B or C denoting the different polarities of the magnetic field generated by adjacent coils.

Figure 4 shows a further embodiment, where the windings are mounted on both the core and around the pump housing. It should be noted that an embodiment with the windings mounted only on the core and with none on the pump housing is also possible, and would have the advantage of a reduced external magnetic field. Embedding the windings in the core such that the magnetic field is generated from this core and radiates outward makes the stray field outside the pump easier to contain and/or manage.

Having windings in the outer housing and in the inner core such there is alignment of N-S poles that are approximately radial to the core provides an increased magnetic field across the gap between these components. This provides a stronger force through the magnetic liquid allowing it to sustain a bigger pressure drop across an equivalent length of magnetic fluid or allow a longer length (greater pumping volume) for a pressure differential equivalent to an inner or outer set of coils only. The currents in the inner and outer coils can be synchronised so that the magnetic poles move synchronously around the swept volume of the pump.

Although the magnetic field is shown as being generated by windings in the above embodiments, it should be clear to the skilled person that they could be generated by other means such as by rotating permanent magnets.

Figure 5 shows a longitudinal section through a single stage pump such as one shown in cross section in Figures 1 and 2 showing the end faces 41 , inlet 45 and outlet 46 and polymer core 32.

Figure 6 shows a longitudinal section through the pumps of Figures 1 and 2, where they are multiple stage pumps. Thus, the exhaust or fluid outlet of the right hand pump stage is input to the inlet of the left hand pump stage via respective inter-stage inlets and exhausts 47, 48. Multiple stage pumps allow for an increased pressure difference between the inlet and outlet.

Although these pumps can be used in a number of applications, in preferred applications the pumps are used as vacuum pumps.

The use of magnetic liquids (ferrofluids, magneto rheological fluids or ionic liquids) to form liquid blades within a rotating magnetic field generated in some cases by a 3-phase induction motor allows a vacuum pump to be formed with no moving mechanical parts. Furthermore, it allows a pump to made from polymer wetted parts, allowing it to be made by 3D printing with no subsequent machining required.

In summary a low power, low cost, minimal maintenance design with easy manufacture no close tolerances required, and the possible 3D printing of pump parts as a single component is provided. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

20 magnetic liquid 22 pumping chamber

30 magnetic field

31 motor winding

32 polymer core 35 Polymer sleeve 41 polymer end faces

45 inlet port

46 outlet port

47 inter-stage inlet

48 inter-stage exhaust