EP4196683A1

EP4196683A1 - Liquid blade pump

Info

Publication number: EP4196683A1
Application number: EP21755039.1A
Authority: EP
Inventors: Paul David Smith; Peter Anthony Mcbrien
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2020-08-11
Filing date: 2021-08-05
Publication date: 2023-06-21
Also published as: CN116057277A; KR20230047388A; US20230279875A1; GB2597951A; WO2022034291A1; JP2023537076A; TW202219388A; GB202012474D0

Abstract

A pump for pumping a gas, the pump comprising: a rotor and a stator; the rotor at least one liquid opening configured for fluid communication with a liquid source. The liquid opening is configured such that in response to a driving force a stream of liquid is output from the opening. The stream of liquid form a liquid blade between the rotor and the stator, gas confined by the stator, the rotor and the liquid blade being driven through the pump along a pumping channel from a gas inlet towards a gas outlet in response to relative rotational motion of the rotor and the stator. The pump is configured such that the pumping channel comprises side walls that slope towards each other from the rotor that comprises the liquid opening towards a further wall of the pumping channel remote from the rotor, such that a distance between the side walls decreases with increasing distance from the liquid opening, a tangent to a mid point of the side walls having an angle of between 5º and 40º with respect to a line perpendicular to an axis of rotation of the rotor.

Description

LIQUID BLADE PUMP

FIELD OF THE INVENTION

The field of the invention relates to pumps.

BACKGROUND

Different types of pumps for pumping gases are known. These include entrapment type pumps, where a gas is captured on a surface inside the pump prior to being removed; kinetic or momentum transfer pumps such as turbomolecular pumps where the molecules of the gas are accelerated from the inlet side towards the outlet or exhaust side, and positive displacement pumps, where gas is trapped and moved from the inlet towards the outlet of the pump.

Positive displacement pumps provide moving pumping chambers generally formed between one or more rotors and a stator, the movement of the rotors causing the effective pumping chamber to move. Gas received at an inlet enters and is trapped in the pumping chamber and moved to an outlet. In some cases the volume of the gas pocket reduces during movement to improve efficiency. Such pumps include roots, and rotary vane type pumps. In order to draw the gas into the chamber, the chamber generally expands and to expel the gas from the chamber, the chamber volume generally contracts. This change in volume can be achieved for example in a rotary vane pump by blades that extend in and out of the pump chamber using devices such as springs, which are themselves subject to wear, or using two synchronised rotors in a roots or screw pump which cooperate with each other and a stator to move a pocket of gas and generate the volumetric changes between inlet and outlet. An additional rotor requires an additional shaft, bearings and timing methods such as gears to synchronise the rotor movements.

Furthermore, in order to minimise or at least 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 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.

GB2565579 discloses a pump that uses a liquid to form the pump blade and thereby addresses some of the problems above.

A liquid blade is by its nature deformable and can be distorted, and distortion in the liquid blade can lead to leakage between the distorted portion of the blade and the solid surface of the rotor or stator to which it should seal.

It would be desirable to provide a pump that is resistant to wear, offers low power consumption and a relatively small pumping mechanism, is relatively inexpensive to manufacture and operate and provides an effective seal between the moving blade and static surfaces.

SUMMARY

A first aspect provides a pump for pumping a gas, said pump comprising: a rotor and a stator; one of said rotor or stator comprising at least one liquid opening configured for fluid communication with a liquid source; said liquid opening being configured such that in response to a driving force a stream of liquid is output from said opening, said stream of liquid forming a liquid blade between said rotor and said stator, gas confined by said stator, said rotor and said liquid blade being driven through said pump along a pumping channel from a gas inlet towards a gas outlet in response to relative rotational motion of said rotor and said stator; wherein said pump is configured such that said pumping channel comprises side walls that slope towards each other from said rotor or stator that comprises said liquid opening towards a further wall of said pumping channel remote from said rotor or stator comprising said liquid opening, such that a distance between said side walls decreases with increasing distance from said liquid opening, a tangent to a mid point of said side walls having an angle of between 5^Q and 40^Q with respect to a line perpendicular to an axis of rotation of said rotor.

The inventors of the present invention recognised that were the elements of a pump to be configured with liquid opening(s) such that liquid output through the openings formed a surface or blade between the elements of the pump, then on rotation of one of the elements with respect to the other, the liquid blade could be used to drive the gas through the pump.

Such a liquid blade is by its nature, deformable, low cost, and generally able to provide good sealing between surfaces of the trapped volume without the need for tight manufacturing tolerances. Furthermore, such a blade is not subject to wear itself and provides very little wear on the surfaces that it contacts.

The blade is formed of a flowing liquid such that the liquid forming the blade is continuously replenished. A surface of the blade acts along with a surface of the elements to confine, trap, isolate or enclose the gas to be pumped. Relative rotation of the rotor and stator cause the trapped gas to be moved from a gas inlet to a gas outlet along a pumping path or channel. Gas to be pumped is located on either side of the blade.

One problem to be addressed with such a pump is that the liquid blade is by its nature deformable and can be distorted, and this may lead to leakage between the distorted portion of the blade and a solid surface of the rotor or stator to which it should seal. In particular, it has been found that there is tapering of the liquid sheet or blade away from the liquid opening(s) and thus, there is an opportunity for gas leakage between the side walls of the pumping channel and the edges of the liquid blade, particularly at radial distances remote from the liquid openings where the cumulative effect of the tapering of the blade is greater. This has been addressed by providing side walls to the pumping channel that are themselves tapered, so that they slope towards each other to compensate for the tapering of the liquid blade, providing for improved sealing along the edge of the liquid blade. In particular, it has been found to be advantageous if the angle of the side wall is selected to be slightly greater than the angle of taper of the liquid blade such that there is not a gap between the blade and the side wall.

The angle of taper of a liquid blade will depend on the type of liquid and in particular, its surface tension and viscosity and on the speed of rotation and the driving force pushing the liquid out through the liquid openings.

In this regard, in operation a surface of the liquid blade comprises a radial dimension between said rotor and stator and an axial dimension perpendicular to said radial dimension and parallel to an axis of rotation. To compensate for the tapering of the blade, the pump is configured such that a dimension of said pumping channel parallel to said axial dimension of said liquid blade decreases with increasing radial distance from said liquid opening.

The angle of the side wall is configured to be similar to but slightly greater than the predicted angle of taper of the liquid blade. It is configured such that a tangent to a mid point of the side walls have an angle of between 5^s and 40² with respect to a line perpendicular to an axis of rotation of said rotor. Preferably between 8^Q and 25^Q more preferably, between 10^Q and 15^Q.

The sloped angle is the angle of much of the side wall, in some embodiments, the middle section of the side wall is straight and sloped at this angle with curved sections at either end.

In some embodiments, said pump is configured such that said side walls of said pumping channel flare outwards towards a junction with said rotor or stator comprising said liquid opening.

In addition to the liquid blade tapering, there may also be distortion of the liquid blade where it first impinges on the sealing edges of the side walls of the pumping channel. This distortion and deviation from its original path can be reduced by flaring the walls outwards such that the sealing gap for the liquid blade is smaller and any deviation has a smaller effect towards the edges. The flaring outwards means that the distance between side wall increases close to and in a direction towards the junction between the stator and rotor, the flaring providing a curved side wall surface.

In some embodiments, said side walls are configured such that a junction between each of said side walls and said further wall is curved.

There is additional disturbance and distortion of the liquid blade at the junction between the further wall and the sloping edge of the side walls and this may be reduced and any potential leakage here inhibited by the use of a curved surface at the junction. The further wall faces the rotor and in some embodiments, is substantially parallel to the axis of rotation of the rotor at its mid point.

In some embodiments, said side walls are symmetrical about an axis perpendicular to a mid point of said further wall.

In some embodiments, said rotor comprises said liquid opening and is mounted to rotate within said stator.

Though all that is required is relative rotational movement between the rotor and the stator, it may be advantageous if it is the rotor that rotates and has the liquid openings as in some cases the rotation of the rotor may provide an additional driving force to the liquid as it exits the openings and forms the blade. In this regard the rotor may in some embodiments, be a hollow cylinder rotationally mounted such that a lower end extends into a liquid reservoir or sump.

Rotational motion helps draw the liquid up the cylinder and expels it through the liquid openings, the liquid forming a blade which on impact with the stator wall runs down the stator walls, along the pumping channel and is collected in the sump to be reused. ln some embodiments, said liquid opening comprises at least one slit, extending longitudinally parallel to an axis of rotation of said rotor.

Although the liquid opening may have a number of forms, in some embodiments it comprises a slit which when liquid exits the slit forms a substantially planar liquid blade. The slit may be angled with respect to the rotational axis but in some embodiments extends longitudinally parallel to the axis of rotation of the rotor. In other embodiments, rather than being a slit, the liquid opening(s) may comprise a plurality of openings arranged along a line.

In some embodiments, said rotor comprises a plurality of slits extending longitudinally parallel to an axis of rotation of said rotor at different positions around an outer circumference of said rotor.

In some embodiments, said stator and rotor are configured such that said pumping channel runs around a circumference of an inner one of said rotor or stator, said gas inlet being arranged to be vertically higher than said gas outlet in operation.

As the liquid that forms the liquid blade will, on hitting a wall of the pumping channel, run down it and collect in the base of the channel, there should be some way of draining the liquid from the pumping channel if the pumping channel is not to become full of liquid. In some cases, the pumping channel is configured such that the gas inlet is higher than the gas outlet when the pump is in operation such that the liquid will drain out through the gas outlet. In some embodiments, the pumping channel runs around the circumference of the stator a single time, or rather slightly less than a whole turn around the circumference. In other embodiments, the pumping channel may run around the circumference of the stator multiple times. ln some embodiments, a lower surface of said pumping channel at said gas outlet is lower than a lower surface of said pumping channel at said gas inlet, and a higher surface of said pumping channel at said gas outlet is higher than a lower surface of said pumping channel at said gas inlet

The liquid blade pushes the gas in a substantially circumferential direction along the direction of rotation of the rotor. Thus, it is advantageous if the pumping channel and gas outlet are also arranged along this path. Thus, although the gas outlet should be below the gas inlet to allow draining of the liquid, it is advantageous if it is only slightly below the gas inlet such that gas is effectively driven by the liquid blade as it rotates.

In some embodiments, a cross sectional area of said pumping channel is configured to increase from said gas inlet to said gas outlet.

Although conventionally the cross-sectional area of the pumping channel may decrease from gas inlet to gas outlet to provide some compression of the gas, in some embodiments, the cross-sectional area increases. Where a liquid blade is used then the liquid that forms the liquid blade is continuously replenished, such that liquid collects within the pumping channel. Draining of the liquid from the pumping channel is required to maintain a free volume for pumping gas, and the liquid while it is within the pumping channel will decrease the volume available for the gas being pumped. Thus, it may be advantageous to increase the cross- sectional area from gas inlet to gas outlet to avoid the pumping channel becoming too constricted by the liquid collecting within it.

In some embodiments, said pump is configured such that said increase in cross sectional area from said gas inlet to said gas outlet and an amount of liquid supplied to said pump during normal operation are selected, such that although the overall cross sectional area increases, the cross sectional area available to gas decreases from said gas inlet to said gas outlet and said gas being pumped is compressed. It may be advantageous to design the pump so that the increasing cross- sectional area and amount of liquid supplied to the pump to form the liquid blade in operation are linked so that the decrease in pumping channel volume that occurs due to the liquid collecting in the pumping channel can be compensated for to some extent by the increase in cross-sectional area but in such a way that the cross-sectional area available to the gas being pumped decreases slightly such that there is some amount of compression of the gas.

In some embodiments, the pump further comprises sealing means between said side walls and said rotor or stator comprising said liquid opening.

In order to reduce leakage of gas and liquid, sealing means may be applied between the side walls of the pumping channel and the rotor or stator comprising the liquid opening. In this regard, where the width of the pumping channel from gas inlet to gas outlet decreases, close to the gas inlet the liquid opening will extend beyond the width of the narrower pumping channel and thus, providing sealing means to reduce the amount of liquid that exits the portion of the liquid opening(s) that do not open into the narrower channel close to the inlet is advantageous.

In some embodiments, said pump comprises a vacuum pump.

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 shows a liquid blade in a pump according to an embodiment;

Figure 2 shows a pump according to an embodiment; and

Figure 3 shows a cross-section through a pumping channel of a pump according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.

Embodiments relate to a pump where the blade of the pump is formed by a liquid such as water that is expelled from one or more apertures in one of the rotor or stator to form a sheet of water that acts as a blade for pushing the fluid to be pumped through the pump. Relative rotation of the stator and rotor cause the fluid to be urged from an inlet to an outlet. When liquid is expelled from the apertures to form a sheet this tapers away from the apertures such that the sheet narrows. This can cause problems of fluid leakage around the edges of the sheet which acts as the blade. Embodiments address this by defining a similarly tapered shaped pumping channel such that the liquid blade adheres to the surface of the pumping channel walls and gaps are avoided or at least inhibited.

In some embodiments, discrete volumes of gas to be pumped are defined within a stator structure by an upper and lower sealing edge and vertical water sheets. These sealed volumes are then driven radially from the inlet to the outlet in a mechanism analogous to a rotary vane pump. One technical challenge is to maintain an effective gas seal between the water sheet and the sealing faces defined by the stator walls. In one embodiment the pump comprises a hollow cylindrical rotor that carries water up from a sump and out through vertical slits to generating rotating sheets of water. As the water exits the slit the top and bottom edges of the sheet taper inwards towards the centre of the sheet as it travels out from the rotor to stator outer wall. This is compensated for by appropriately sloping the upper and lower sealing edges of the pumping channel walls to match the tapering of the water sheet. In addition, where the sheet first impinges on the sealing edges, the leading edge, it is disturbed and deviates from its original path. This is addressed by introducing a suitable curvature to the slope at the leading edge (inner diameter). It was also observed that at the outer diameter at the corner between the outer stator wall and the sloping edge additional disturbance to the water sheet occurred. This is addressed by introducing a radius at this corner. This combination defines a unique, and novel, geometry for the stator channel .

Figure 1 schematically shows the tapering of blade 40 formed of a sheet of liquid expelled through liquid opening 12, which in this embodiment has the form of a slit formed in rotor 10, the edges of the slit defining either edge of the blade 40. In this example, the tapering angle is shown as 20° It should be understood that this angle may vary depending on both the length and the width of the aperture and the force with which the liquid is expelled through the aperture along with the viscosity and surface tension of the liquid. The liquid is in this embodiment water.

Figure 2 schematically shows a pump according to an embodiment. In this embodiment, rotor 10 is mounted to rotate within stator 20. Rotor 10 has a slit 12 through which water is expelled forming blade 40 such as is shown in Figure 1 . As the rotor 10 rotates with respect to stator 20 the blade pushes gas around through the pumping channel 38 within stator 20 from an inlet 52 to an outlet 54.

The base of inlet 52 is slightly higher than the base of outlet 54 which allows liquid from the liquid blade that collects within the pumping channel 38 during the pumping of the gas, to flow from inlet 52 to outlet 54 where it is exhausted.

In this embodiment, rotor 10 is a hollow cylinder and the centrifugal force caused by rotation of the rotor causes liquid to rise up from a sump and be expelled through liquid slit 12. In some embodiments, there may be a pump to send water towards and through the slit 12.

The cross-sectional area of inlet 52 is smaller than the cross-sectional area of outlet 54 in this embodiment and this increase in cross sectional area from inlet to outlet helps compensate for the decrease in available volume for any fluid or gas being pumped that occurs due to the accumulation of the liquid from the liquid blade within the pumping channel 38. The side walls of the pumping channel 38 are sloped such that the cross section of the pumping channel tapers in a corresponding way to the liquid blade of Figure 1 . This avoids or at least inhibits gaps being formed between the side walls and the liquid blade towards the outer edges of the pumping channel, further from the rotor, where the tapering is most pronounced.

Figure 3 shows a cross-sectional view of pumping channel 38 where the form of this channel can be seen more clearly. In this embodiment, the side walls 34 are sloped at an angle of 25° when taken from a tangent at the midpoint 34b of the side walls. The side walls towards the rotor 34a have a more pronounced taper, such that they flare outwards in a curved manner and are further apart than they are towards the middle of the walls. The ends of the side walls 34c towards the further wall 36 are curved so that there are no sharp angles as the side walls curve round to form the further wall and disruptions in the flow are reduced. In this regard the side walls are those that extend substantially radially, while the further wall faces the rotor and runs substantially axially, parallel to the axis of rotation.

In operation as the liquid exits the slit 12, the top and bottom edges of the blade taper inwards towards the centre of the blade as it travels out from the rotor towards the further wall 36. This tapering is matched and compensated for by appropriately sloping the upper and lower side walls 34 of the stator that along with further wall 36 form the pumping channel 38. This tapering is designed to substantially match the tapering of the water sheet with slightly more taper to avoid or at least reduce any gaps.

Additionally, where the sheet or blade first impinges on the side walls 34a it is disturbed and deviates from its original path. This is addressed by introducing a suitable curvature to the slope of the side wall adjacent to the leading edge 34a such that the distance between the side walls 34 is greater at this junction between rotor 10 and stator 20 and has a curved shape. It has also been observed that at the end 34c of the side walls at the junction with the further wall 36 additional disturbance to the liquid sheet occurs. This can be reduced by introducing a radius at this corner such that there is curvature here. In this way, the geometry and cross-section of channel 38 is adapted to the properties of the liquid sheet and provides effective sealing for pumping gas.

As in this embodiment, the slit 12 is longer than the width of channel 38 closer to the inlet, as the channel has a smaller axial dimension here, sealing means 32 are provided between the stator and rotor on either side of the pumping channel, to avoid or at least inhibit liquid leakage from the pumping channel.

As can be seen from the cross section, the lower side wall slopes vertically downwards from the inlet to the outlet, such that liquid accumulating in the pumping channel 38 drains at the outlet.

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

10 rotor

12 liquid opening

20 stator 32 sealing means

34 side wall

36 further wall

38 pumping channel

40 liquid blade 52 inlet

54 outlet

Claims

1 . A pump for pumping a gas, said pump comprising: a rotor and a stator; one of said rotor or stator comprising at least one liquid opening configured for fluid communication with a liquid source; said liquid opening being configured such that in response to a driving force a stream of liquid is output from said opening, said stream of liquid forming a liquid blade between said rotor and said stator, gas confined by said stator, said rotor and said liquid blade being driven through said pump along a pumping channel from a gas inlet towards a gas outlet in response to relative rotational motion of said rotor and said stator; wherein said pump is configured such that said pumping channel comprises side walls that slope towards each other from said rotor or stator that comprises said liquid opening towards a further wall of said pumping channel remote from said rotor or stator comprising said liquid opening, such that a distance between said side walls decreases with increasing distance from said liquid opening, a tangent to a mid point of said side walls having an angle of between 5^Q and 40^Q with respect to a line perpendicular to an axis of rotation of said rotor.

2. A pump according to claim 1 , wherein said side walls are sloped such that said angle of a tangent to a mid point of said side wall with respect to a line perpendicular to an axis of rotation of said rotor, is between 8^Q and 25^Q preferably, between 10^Q and 15^Q.

3. A pump according to any one of claims 1 or 2, said pump being configured such that said side walls of said pumping channel flare outwards towards a junction with said rotor or stator comprising said liquid opening.

4. A pump according to any preceding claim, said pump being configured such that a junction between each of said side walls and said further wall is curved

5. A pump according to any preceding claim, said side walls being symmetrical about an axis perpendicular to a mid point of said further wall.

6. A pump according to any preceding claim, wherein said rotor comprises said liquid opening and is mounted to rotate within said stator.

7. A pump according to any preceding claim, wherein said liquid opening comprises at least one slit, extending longitudinally parallel to an axis of rotation of said rotor.

8. A pump according to any preceding claim, wherein said stator and rotor are configured such that said pumping channel runs around a circumference of an inner one of said rotor or stator, said gas inlet being arranged to be vertically higher than said gas outlet in operation.

9. A pump according to claim 8, wherein a lower surface of said pumping channel at said gas outlet is lower than a lower surface of said pumping channel at said gas inlet, and a higher surface of said pumping channel at said gas outlet is higher than a lower surface of said pumping channel at said gas inlet

10. A pump according to any preceding claim, wherein a cross sectional area of said pumping channel is configured to increase from said gas inlet to said gas outlet.

1 1. A pump according to claim 10, wherein said pump is configured such that said increase in cross sectional area from said gas inlet to said gas outlet and an amount of liquid supplied to said pump to form said liquid blade in normal operation are selected such that a cross sectional area of said pumping channel available to gas decreases from said gas inlet to said gas outlet and said gas being pumped is compressed. - 16 -

12. A pump according to any preceding claim, further comprising sealing means between said side walls and said rotor or stator comprising said liquid opening.

13. A pump according to any preceding claim, where said pump comprises a vacuum pump.