GB2597952A

GB2597952A - Liquid blade pump

Info

Publication number: GB2597952A
Application number: GB2012475.6A
Authority: GB
Inventors: David Smith Paul; Anthony Mcbrien Peter
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2020-08-11
Filing date: 2020-08-11
Publication date: 2022-02-16
Also published as: TW202219387A; JP2023537077A; CN116075639A; GB202012475D0; KR20230047389A; US20230296095A1; EP4196684A1; GB2597952A8; WO2022034292A1

Abstract

A pump, for pumping a gas, having a rotor 10 and a stator 20 one of which has at least one liquid opening 12 from which is driven a stream of liquid that forms a liquid blade, or fluid vane, between the rotor and the stator such that, gas is confined and driven along a pumping channel (38, fig.5) by the relative rotation of the rotor and stator from an inlet 52 towards an outlet 54 and a cross-sectional area of the pumping channel increases from the gas inlet to the gas outlet. The radial width and/or axial width of the pumping channel, which may be helical (fig.2) or spiral, can increase towards the outlet as too can the size of the liquid opening and hence the volume of the liquid blade. The liquid opening may be a slit which is arranged as a helix around the rotor, or it may be formed of multiple smaller openings in a line. The pump can have a seal (32, fig.5) and be used as a vacuum pump that compresses the gas by having a decreasing cross-section of available space in the pumping channel even when the channel increases in cross-section.

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 -2 -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.

io 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 means of pumping gases between an inlet and outlet.

SUMMARY

A first aspect provides a pump for pumping a gas, said pump comprising: a rotor and a stator; at least 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 a cross sectional area of said pumping channel is configured to increase from said gas inlet to said gas outlet.

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 able to provide good sealing between surfaces of the -3 -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.

However, as the blade is formed of a flowing liquid, the liquid forming the blade is continuously replenished. One of the challenges of pumps that use liquid blades is maintaining a sufficient free volume for gas movement within the pumping channel as liquid forming the liquid blade accumulates within the channel during operation. Generally the cross-sectional area of a pumping channel is configured to decrease between inlet and outlet to provide compression of the gas during pumping, which leads to a more efficient pump. Embodiments provide an increase in cross-sectional area between the inlet and outlet. This increase is used to compensate for the reduction in volume available to the gas being pumped due to the accumulation within the pumping channel of liquid from the constantly replenished liquid blade. The accumulation of liquid increases from the inlet to the outlet as the liquid drains along the channel and thus, an increase in the cross sectional area from the inlet to the outlet can be used to address this, and provide an acceptable change in volume from inlet to outlet that provides for a desired pumping speed and acceptable efficiency.

In some embodiments, a distance between said rotor and said stator increases from said gas inlet to said gas outlet.

One way in which the cross-sectional area may be increased is to increase the distance between the rotor and the stator. This may be done by tapering one or the other or both. One potential issue with this is that the length of the liquid blade will also increase as the distance between the rotor and the stator increases and this can make it less robust. This decrease in robustness may require some additional measures such as an increase in liquid flow to maintain

an acceptable blade. -4 -

In some embodiments, said pump is configured such that during operation a quantity of liquid output through said liquid opening increases from said gas inlet to said gas outlet.

The amount of liquid that is input through the liquid openings may be increased from the gas inlet towards the gas outlet. This may be advantageous for a number of reasons. In the first place, any liquid entering near the gas inlet may need to travel along the pumping channel to be drained and thus, it is advantageous to limit the amount of liquid entering nearer the inlet, as it may need to travel along most of the length of the pumping channel and liquid within the pumping channel reduces the available volume for gas being pumped. Furthermore, in embodiments, where the distance between the stator and rotor increases from the inlet to the outlet then to enable the liquid blade to be more robust where it is covering a larger area it is advantageous if additional liquid is supplied. In this regard, increasing the blade length can be compensated for and an equally robust blade maintained by correspondingly increasing the quantity of water supplied.

In some embodiments, a cross section of said liquid opening is greater towards said gas outlet than towards said gas inlet.

The increase in the amount of liquid that is introduced through the liquid opening may be achieved by increasing the cross-section of the liquid opening towards the gas outlet. Alternatively, it may be achieved by increasing the exit velocity of the liquid at the slit. Increasing the width of the slit is more energy efficient than an increase in the exit velocity of the water. However, there is still a power consumption penalty associated with the increased water forming the water blade.

In some embodiments, said liquid opening comprises a slit. -5 -

A long narrow opening in the form of a slit may provide an effective water blade. In some embodiments, rather than a single long, narrow opening, there may be a plurality of liquid openings arranged along a line, liquid from each opening coalescing with liquid from neighbouring openings to form a blade along that line.

Although the slit may be angled with the respect to a longitudinal axis in some embodiments, the slit extends longitudinally parallel to an axis of rotation of said rotor.

In some embodiments, where the distance between the rotor and stator increases from the gas inlet to the outlet by tapering one of the rotor or stator, then where the liquid opening is a slit the slit may have an increased width towards the gas outlet where the distance between the rotor and stator is increased, providing a blade of increased thickness and correspondingly increased robustness.

In other embodiments, said slit is arranged in the form of a helix extending around an axis of rotation of said rotor.

A helical pumping channel may be defined, by a helical slit that forms a helical liquid blade.

In some embodiments, an angle of said helix changes from said gas inlet towards said gas outlet such that a pitch of said helix increases towards said gas outlet.

The increase in cross sectional area of the pumping channel may be achieved by increasing the pitch of the helical liquid opening from the inlet to the outlet. In this way problems with an increased distance between rotor and stator and requirements for additional liquid to maintain robustness of the liquid blade do not arise. -6 -

The slit may be a single aperture extending along a line or helical path, or it may be formed by a plurality of apertures arranged along a line or helical path.

In some embodiments, one of said rotor and stator comprises a helical protrusion extending towards the other element and defining a helical path of said pumping channel, the other element comprising said liquid opening.

One form of pump that uses a liquid blade may be a screw pump with a helical path formed by helical protrusions extending between the rotor and stator.

In some embodiments, a pitch of said helical protrusion increases from said gas inlet to said has outlet.

An alternative way of increasing the cross-sectional area of the pumping channel is to increase the pitch of the helical protrusions. This may be advantageous as then the distance between the rotor and the stator may remain constant and thus, the amount of liquid required for the liquid blade extending through a same cross-sectional area of the liquid opening can stay constant.

In some embodiments, the cross sectional area of said pumping channel is defined by a radial length being a distance between said rotor and said stator and an axial width being a dimension of said pumping channel perpendicular to said radial length, said axial width increasing from said gas inlet to said gas outlet.

As noted previously, where the radial lengths of the pumping channel increases then to maintain a robust blade the amount of liquid supplied may need to be increased. Where the axial width of the channel increases then the size of the liquid opening as it covers the width of the pumping channel will automatically correspondingly increase, and there is no need for any further adjustments. It may therefore be desirable for the axial width to increase from the gas inlet to the gas outlet. In this regard the axial width is parallel to the axis of rotation. -7 -

In some embodiments, the rotor and stator are mounted one within the other.

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

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 lower surface of the gas inlet is higher than the lower surface of 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 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. -8 -

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 provided 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, a cross sectional area of said pumping channel is defined by a radial length, said radial length being a distance between said rotor and said stator and an axial width, said axial width being a dimension of said pumping channel perpendicular to said radial length, said pump being configured such that said axial width of said pumping channel decreases with increasing radial distance from said liquid opening.

In some embodiments the pumping channel may be tapered such that it becomes narrower away from the liquid openings. The liquid blade may itself taper as it leaves the liquid opening(s), and thus, it may be advantageous to taper the channel in a corresponding manner and thereby avoid, or at least reduce gaps forming between the side walls and the blade.

In some embodiment, 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. -9 -

The volume available to the pumped gas depends both on the cross sectional area of the pumping channel and on the liquid within the pumping channel. The liquid within the pumping channel will increase from the inlet to outlet and can be determined from the liquid supplied to the pump during normal operation and its rate of drainage. The pump may be configured such that the increase in cross sectional area from the gas inlet to the gas outlet of the pumping channel is selected in dependence upon the estimated amount of liquid that there will be accumulated in the pumping channel during normal operation. In this way a cross sectional area of the pumping channel available to the gas can be controlled and in some cases may be controlled to decrease slightly from said gas inlet to said gas outlet such that the gas being pumped is compressed.

In summary the liquid supply to the pump through the liquid opening to form the liquid blade will accumulate within the pump from the gas inlet to the gas outlet and will drain out with the gas at the gas outlet. This will lead to increase in liquid along the pump channel from the gas inlet to the gas outlet with a corresponding decrease in available area for the gas that is being pumped. This may be compensated for by an increase in the cross-sectional area of the pumping channel from the gas inlet to the gas outlet. In some cases, the pump is configured such that these two are linked and the design is such that the free volume for gas decreases from pump inlet to pump outlet such that there is a compression of the pumped gas, the amount of decrease being controlled to provide a controlled amount of compression which allows an efficient pump with an effective liquid blade.

In this regard, the increase in cross sectional area may be a gradual increase along the lengths of the pumping channel such that it is linked to the accumulation of liquid within the pumping channel.

In some embodiments, said pump comprises a vacuum pump.

-10 -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 pump with a helical pumping channel according to an embodiment; Figure 2 shows an alternative embodiment of the helical path pump; Figure 3 shows a liquid blade rotary vane type pump according to an embodiment; Figure 4 shows an overview of the path through the pump of Figure 3; and Figure 5 shows further views of the pump of Figure 3.

DESCRIPTION OF THE EMBODIMENTS

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

Embodiments of the pump generate rotating sheets of water to separate the pumped gas into discrete volumes and to drive these volumes from an inlet to an outlet. During the passage from inlet to outlet an increasing volume of water is introduced into the mechanism until at the outlet both the water and the gas exit at the exhaust. One of the technical challenges is to maintain sufficient free volume for gas movement through the mechanism. This can be addressed by increasing the cross sectional area of the channel through which the gas is being moved. One approach to address this whilst reducing power consumption is to increase the cross sectional area as a function of distance from the inlet, which in some embodiments is dependent on rotation angle.

Embodiments of the pump comprise a hollow cylindrical rotor that carries water up from the sump and out through vertical slits to generating rotating sheets of water. These sheets of water separate the pumped gas into discrete volumes and drive these from the inlet to the outlet. In one embodiment these discrete volumes are generated within a screw thread and the gas is driven down a helical channel. In another embodiment these discrete volumes are simply defined by io an upper and lower sealing edge and driven radially from the inlet to the outlet in a mechanism analogous to a rotary vane pump. In yet another embodiment, the liquid openings themselves form a screw thread, providing a helical liquid blade for pumping gas from an inlet to an outlet.

In all of these embodiments, from the inlet to the outlet an increasing volume of liquid, generally water is introduced into the mechanism until at the outlet both the water and the gas exit at the exhaust. One of the technical challenges therefore is to maintain sufficient free volume for gas movement through the mechanism. This can be achieved by increasing the cross-sectional area of the channel through which the gas is being moved by either increasing the height of the channel and/or by increasing the radial distance between the rotor and the stator wall.

However, simply increasing the cross-sectional area uniformly can be inefficient with regards to energy consumption and provides only limited control over the change in sealed gas volume. In some embodiments, the amount that the cross sectional area increases is set to be dependent upon the amount of liquid added and any desired compression. The liquid blades are continuously replenished and the liquid forming the blades will accumulate in the pumping channel reducing the volume available for the pumped gas. This is predictable and the design can estimate the change in volume due to accumulating liquid, and the desired compression and design the increase in cross sectional area accordingly.

-12 -In one embodiment an energy efficient approach is to increase the cross-sectional area as a function of distance along the pumping channel from the inlet to the outlet, in some embodiments this equates to rotation angle. This allows power consumption to be improved whilst providing the required volumetric compression of the gas. Some example embodiments are shown in the following section.

Figure 1 shows the pump having a helical screw stator form where the increase io in cross-sectional area of the pumping channel is provided by an increase in radial distance between the stator 20 and rotor 10 from the inlet 52 to the outlet 54. Having a stator form that is tapered as in this embodiment provides the increased cross-sectional area, however there is an increased distance between the rotor and stator and in order to compensate for this the exit velocity of the liquid, in this embodiment water or the thickness of the water sheet must be increased. In this embodiment the thickness of the water sheet is increased by providing an increased width of slit 12 through which water exits towards the outlet 54 side of the pump. This is more energy efficient than an increase in the exit velocity of the water. However, there is still a power consumption penalty associated with the increased water forming the water blade.

In other embodiments the rotor may be tapered as well as the stator and the increase in rotor diameter towards the outlet leads to an increase in exit velocity of the water exiting the slit 12. The angle of rotor taper may be less than that of the stator taper, leading to an increased distance between them and a corresponding increase in cross-sectional area towards the outlet. Increasing the diameter of the rotor is an energy efficient way of providing the desired increase in exit velocity of the water towards the outlet.

Figure 2 shows a second and in some cases preferred embodiment where the radial distance between rotor 10 and stator 20 is constant. The increase in cross-sectional area of the pumping channel is provided by a change in pitch from the -13 -inlet 52 to the outlet 54. This allows slit 12 to have a constant width and provides a correspondingly constant width water blade. This may be more energy efficient than the embodiment of Figure 1.

Although the embodiments of Figure 1 and Figure 2 show a straight water blade, they are also applicable to a helical water blade that can be formed with a helical slit. This can be used with a corresponding helical screw on the stator or indeed with a stator not having a profile. Again the pitch of the slit forming the water blade may vary to provide the increased cross-sectional area of the pumping channel and/or the distance between the rotor 10 and stator 20 may vary to provide this increase in cross-sectional area.

Figure 3 shows an alternative embodiment which is analogous to a rotary vane pump. In this embodiment, rotor 10 is mounted within stator 20 and comprises slit 12 through which liquid exits in operation to form the liquid blade. Pumping channel 38 is formed by the walls of stator 20 and on rotation of rotor 10 gas is driven by the blade from inlet 52 to outlet 54. Inlet 52 has a cross-sectional area which is smaller than outlet 54 to accommodate a reduction in volume that will occur due to the liquid from the liquid blade accumulating within the channel as the water blade rotates. The floor of the pumping channel at the inlet is higher than the floor of the pumping channel at the outlet 54 such that during operation any liquid accumulating within the pumping channel will drain and exit with the gas at outlet 54. As can be seen the cross-sectional area 38 of the pumping channel increases from the inlet 52 to outlet 54.

Figure 4 shows an overview of the path through the pumping channel from the inlet to the outlet. As can be seen the path follows an almost circular route such that the rotational movement drives the gas in an efficient manner. There is a slight vertical aspect to the circular path due to the requirement for drainage but this is small making this an efficient way of pumping gas. The helical arrangement has a greater vertical component imparted to the gas and this is not -14 -in the direction of rotation, and thus, of the blade, so will not be provide as efficient pumping.

Figure 5 shows the pump of Figures 3 and 4 sideways on. Pumping channel 38 is formed in the stator 20 or of the pump. The rotor 10 is rotatably mounted within the stator 20 and comprises one or more slits 12 that form a liquid blade to push gas along pumping channel 38. The cross sectional area of pumping channel 30 increases from the inlet to the outlet and the lower surface or floor of the pumping channel is in a slightly lower position at the outlet compared to the inlet. Furthermore, sealing members 32 are provided to seal between the stator and the rotor. In this regard, the lengths of slit 12 is longer than the length of the channel for at least some of the circumference of the stator closer to the inlet and thus, to inhibit liquid expelled by slit 12 leaking out of the pump, seals 32 are provided at either edges of the pumping channel.

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.

-15 -

REFERENCE SIGNS rotor

12 liquid opening stator 32 sealing means 38 pumping channel 52 inlet 54 outlet

Claims

-16 -CLAIMS1. A pump for pumping a gas, said pump comprising: a rotor and a stator; at least 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 io 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 a cross sectional area of said pumping channel is configured to increase from said gas inlet to said gas outlet.
2. A pump according to claim 1, wherein a distance between said rotor and said stator increases from said gas inlet to said gas outlet.
3. A pump according to any preceding claim, wherein said pump is configured such that during operation a quantity of liquid output through said liquid opening increases from said gas inlet to said gas outlet.
4. A pump according to claim 3, wherein a cross section of said liquid opening is greater towards said gas outlet than towards said gas inlet.
5. A pump according to any preceding claim, wherein said liquid opening forms a slit.
6. A pump according to claim 5, wherein said slit extends longitudinally parallel to an axis of rotation of said rotor.
-17 - 7. A pump according to claim 5, wherein said slit is arranged in the form of a helix extending around an axis of rotation of said rotor.
8. A pump according to claim 7, wherein an angle of said helix changes from said gas inlet towards said gas outlet such that a pitch of said helix increases towards said gas outlet.
9. A pump according to any preceding claim, wherein one of said rotor and stator comprises a helical protrusion extending towards the other element and defining a helical path of said pumping channel, the other element comprising said liquid opening.
10. A pump according to claim 9, wherein a pitch of said helical protrusion increases from said gas inlet to said has outlet.
11. A pump according to any one of claims 1 to 5, 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.
12. A pump according to claim 11, said pump further comprising sealing means between said side walls and said rotor or stator comprising said liquid opening.
13. A pump according to claim 11 or 12, 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
14. A pump according to any preceding claim, wherein a cross sectional area of said pumping channel is defined by a radial length being a distance between -18 -said rotor and said stator and an axial width being a dimension of said pumping channel perpendicular to said radial length, said axial width increasing from said gas inlet to said gas outlet.
15. A pump according to any preceding claim, wherein said rotor comprises said liquid opening and is mounted to rotate within said stator.
16. A pump according to any preceding claim, wherein a cross sectional area of said pumping channel is defined by a radial length, said radial length being a distance between said rotor and said stator and an axial width, said axial width being a dimension of said pumping channel perpendicular to said radial length, said pump being configured such that said axial width of said pumping channel decreases with increasing radial distance from said liquid opening.
17. A pump according to any preceding claim, wherein said pump is configured such that said increase in cross sectional area from said gas inlet to said gas outlet is selected based on an amount of liquid supplied to said pump to form said liquid blade in normal operation, 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.
18. A pump according to any preceding claim, where said pump comprises a vacuum pump