GB2535467A

GB2535467A - Acoustic pump

Info

Publication number: GB2535467A
Application number: GB1502540.6A
Authority: GB
Inventors: Gilmour Sean
Original assignee: PUBBLE HILL Ltd
Current assignee: PUBBLE HILL Ltd
Priority date: 2015-02-16
Filing date: 2015-02-16
Publication date: 2016-08-24
Anticipated expiration: 2035-02-16
Also published as: GB2535467B; GB201502540D0

Abstract

An acoustically driven pump comprises a chamber 20 having opposed first and second side walls 11, 12, and first and second end walls 13, 14. At least a portion of the first side wall is defined by means for propagating an acoustic wave (e.g. a piezoelectric actuator) within said chamber at a predetermined wavelength in order to generate a standing wave between the first and second side walls. One or more apertures 15, 16 are provided in each of the first and second end walls such that pressure differentials within the chamber adjacent to the aperture(s) caused by the standing wave cause fluid to flow through the aperture(s) in a direction substantially parallel to the first side wall. One or more of the apertures may be tapered, and/or provided with a backflow lip, to provide greater flow resistance in one direction than the other. The chamber may be provided in a further housing, with a region being defined there between.

Description

Acoustic pump This invention relates to an acoustically driven pump for pumping a fluid, such as air.

There are currently a number of systems designed to pump air in one direction. It is often desirable to provide small devices for generating air movement for cooling of electronic components and other small items. In once example of such device a vibrating transducer is used to displace air through an orifice. As illustrated in Figure 1, a moveable wall of a piezoelectric transducer 1 defines a lower wall of a cavity 2, a small outlet orifice 3 being provided at an upper end of the cavity 2, opposite the piezoelectric transducer 1. Air is compressed within the cavity 2 between the piezoelectric transducer 1 and the outlet orifice 3 when the transducer is energised. The size of the cavity 2 is such that a deflection of the moveable wall of the transducer 2 causes a significant percentage change in the volume of the cavity. Thus displacement of the moveable wall of the transducer 1 in one direction can cause air to be forced through the orifice 3, while air is drawn into the cavity 2 via the orifice 3 when the moveable wall of the transducer 2 moves in the opposite direction. When air is forced out of the orifice 3, it is ejected at high speed, mostly in a direction perpendicular to the cavity 2 (and to the piezoelectric transducer 1).

The outlet orifice 3 of the cavity 2 is aligned with a specially shaped aperture 4 in a housing 5 surrounding the cavity, such that said aperture 4 receives said high speed jet of air from the outlet orifice 3 of the cavity 2. The aperture 4 is specially shaped such that, when exposed to a pressure difference in one direction (i.e. inwardly into the housing 5), the aperture 4 allows a small amount of air to pass, while a pressure difference in the other direction (i.e. outwardly from the housing 5) allows significantly more air to pass through. This, coupled with the way the air diffuses into the cavity 2 when the moveable wall of the transducer 1 deflects downwardly, gives a significant net flow out of the aperture 4, air being entrained into a passage 6 defined between the cavity 2 and the outer wall of the housing 5 as shown in Figures 2 and 3.

This design depends on three main parameters to cause and optimise net airflow in one direction:- (1) The shape of the outlet aperture 4; (2) A generation of a jet of pressurised air to enter the specially shaped outlet 5 aperture 4 from the orifice 3 of the cavity 2; and (3) An area adjacent the small orifice 3 of the cavity 2 that diffuses air moving into the cavity 2 when the transducer wall deflects downwardly. This means that most air that enters the cavity 2 through the small hole 3 is from the space directly above the small hole 3 and only a smaller amount of air is from the specially shaped aperture 4.

This design has the following drawbacks:- (1) It is expensive and complex, with relatively high manufacturing costs; (2) Because of airflow patterns, it is more suited to only a single jet with limited airflow; and (3) There needs to be a space above and below the pump, increasing the minimum operating height of the device.

According to the present invention there is provided an acoustically driven pump for pumping a fluid comprising a chamber having opposed first and second side walls and first and second end walls, at least a portion of the first side wall being defined by means for propagating an acoustic wave in a fluid within said chamber at a predetermined wavelength in order to generate a standing wave between said first and second side walls, one or more apertures being provided each of said first end and second side walls such that pressure differentials within said chamber adjacent said one or more apertures caused by said standing wave causes fluid to flow through said one or more apertures in a direction substantially parallel to said first side wall.

In one embodiment at least one first aperture is provided in said first end wall and at least one second aperture is provided in said second end wall, wherein said at least one first aperture is adapted to provide a greater flow resistance to the passage of a fluid out of the chamber than to the passage of said fluid into the chamber, and/or said at least one second aperture is adapted to provide a greater flow resistance to the passage of said fluid into the chamber than to the passage of said fluid out of the chamber.

Said at least one first aperture may have a funnel shape narrowing towards an outer side of said first end wall. Alternative shapes are envisaged, for example a simple hole with semi-circular edges defining an tapered or narrowing region on an inner side of said first end wall.

Said at least one second aperture may be provided with a peripheral backflow lip extending into the chamber.

In a second embodiment said chamber is located within a housing having a first housing end wall adjacent the first end wall of the chamber to define a first region therebetween and a second housing end wall adjacent and the second end wall of the chamber to define a second region therebetween, the housing including at least one diffuser passage extending between said first and second regions, an outlet orifice being provided in said first housing end wall and an inlet orifice being provided in said second housing end wall.

Said inlet orifice may be adapted to provide a greater flow resistance to the passage of a fluid out of the chamber than to the passage of said fluid into the chamber, and/or said outlet orifice is adapted to provide a greater flow resistance to the passage of said fluid into the chamber than to the passage of said fluid out of the chamber. The outlet orifice may have a funnel shape narrowing towards an outer side of the housing and/or may have a peripheral backflow lip extending from an outer wall of the housing. The inlet orifice may be provided with a peripheral backflow lip extending towards the chamber.

Preferably the outlet orifice is aligned with an aperture in the first end wall of the chamber, the inlet orifice being offset from the or each aperture in the second wall of the chamber.

In one embodiment the first end wall of the chamber is provided with a single aperture, said single aperture being aligned with the outlet orifice of the housing, the second end wall of the chamber being provided with two apertures, said apertures in said second end wall of the chamber being located on either side of the inlet orifice of the housing.

The means for propagating an acoustic wave within said chamber may comprise a piezoelectric transducer or alternatively any other means for generating an acoustic wave, such as a speaker. Where the means for propagating an acoustic wave comprises a piezoelectric transducer, such transducer may comprise at least a portion of the first side wall of the chamber.

An acoustic pump in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying 15 drawings, in which:-Figure 4 is a sectional view through an acoustic pump in accordance with an embodiment of the present invention; Figures 5 and 6 is a further sectional view of the pump of Figure 4 illustrating the operation of the pump; Figure 7 is a sectional view through an acoustical pump in accordance with a further embodiment of the present invention.

Figure 8 is a further sectional view of the pump of Figure 7.

As illustrated in a Figures 4 to 6, an acoustically driven pump in accordance with a first embodiment of the present invention comprises an elongate hollow body 10 defining a chamber 20 having opposed first and second side walls 11,12 and first and second end walls 13,14. The first side wall 11 is defined by a moveable wall of a piezoelectric transducer for propagating an acoustic wave within said chamber 20 at a predetermined wavelength in order to generate a standing wave between said first and second side walls 11,12 of the chamber 20.

A first aperture 15 is provided in the first end wall 13 of the chamber 20. A second aperture 16 is provided in the second end wall of the chamber 20, opposite the first aperture 15.

The first aperture 15 is adapted to provide a greater flow resistance to the passage of a fluid out of the chamber than to the passage of said fluid into the chamber, said second aperture 16 being adapted to provide a greater flow resistance to the passage of said fluid into the chamber than to the passage of said fluid out of the chamber. The acoustic pump in accordance with present invention, rather than essentially squashing air out of a cavity to create a high intensity jet, as in the case of known devices, creates high intensity pressure changes in the vicinity of the first and second apertures 15,16 as a result of the creation of a half wave acoustic standing wave within the chamber.

The transducer does not significantly change the volume of air in the chamber as it deflects fully in either direction. Instead deflection of the transducer generates a standing wave within the chamber, causing high pressure changes at the first and second apertures 15,16 due to such apertures 15,16 being aligned with the antinodes of the standing wave. This causes a pressure difference at the first and second apertures 15,16, causing air to flow therethrough.

The net airflow in and out of the chamber 20 is proportional to the incident air velocity/pressure to and from the first and second apertures 15,16. Using a standing wave increases the pressure difference across the apertures 15,16 and maximises the performance of the system, using less power than would otherwise be required to produce pressure levels of the required intensity.

When a fluid is pushed through a small hole in a specific direction with sufficient force, it will form a jet and entrain fluid in its vicinity increasing flow volume. If fluid is sucked in through such a small hole, fluid is sucked in from all directions and does not cause a net flow in any specific direction. When fluid is pushed and pulled through a small hole in an oscillating manner, the pushing action causes a jet, entraining additional fluid while the pulling/sucking action does not significantly affect the average movement of fluid caused by the pushing/jet action. This causes a net flow of fluid in one direction.

In the embodiment shown in the drawings, the or each first aperture 15 has a funnel 5 shaped portion 17 narrowing towards an outer side of said first end wall. This portion 17 can assume a number of different geometries but all have the effect of gathering as much air from the nearby high pressure zone. This funnel shaped portion 17 is not present on the second aperture 16. The first aperture 15 may also have a peripheral backflow lip 18 at an outer end thereof to reduce the amount of air 10 that gets sucked back into the chamber 20 through the first aperture 15 when the pressure in the chamber 20 changes to an average negative pressure.

The second aperture 16 may be provided with a peripheral backflow lip 19 on an inner side thereof for to reducing the amount of air that gets pushed out of the 15 chamber 20 through the second aperture 16 when the pressure in the chamber 20 changes to an average positive pressure.

The overall height of the acoustic pump can be reduced by increasing the frequency, and therefore reducing the length, of an optimal half wave standing zo wave.

By virtue of the positioning of the first and second apertures 15,16 in the first and second end walls 13,14 of the chamber 20, the air flow created by the pump is parallel to the transducer (first side wall 11), therefore suiting cooling applications 25 within low profile devices.

An upper side of the second side walll2 of the chamber 20 of the acoustic pump may be placed against a surface to be cooled, acting in a way similar to traditional pump/heatsink combinations. The body of the acoustic pump could be inverted to 30 contact the second side wall 12 of the chamber against a hot surface for cooling.

One or more orifices can be strategically placed at either end of the acoustic pump to improve performance in entraining air to increase overall airflow. There could be any number of orifices. Preferably the orifices should be lined up with the antinodes. Different hole position strategies could be taken advantage of.

An acoustic pump in accordance with the present invention can be used in a liquid 5 or gas.

The frequency of acoustic waves used to generate a standing wave within the chamber 20 of the pump is preferably ultrasonic to reduce unwanted audible noise from the system. However, it is envisaged that other frequencies could be used, 10 including audible frequencies.

In a typical system, the frequency of the acoustic wave could be 40kHz, with a wavelength of approximately 8.575mm. The height of the resonant chamber in the acoustic pump is preferably half this wavelength, which is approximately 4.288mm.

The approximate diameter of the first and second apertures 15,16 at such frequency is approximately 1mm.

An acoustic signal with a frequency content of more than one frequency may be applied by the transducer. There is an optimal aperture size for net airflow for each zo frequency.

More than one of one or both of the first and second apertures 15,16 may be used and they may have different sizes to accommodate different frequencies.

Ambient noise from an acoustic speaker used for audible audio applications (for example a mobile phone speaker playing music) can cause air to move through the special orifice causing air to flow with or without the need for a separate transducer operating in the pump.

A high frequency ultrasonic acoustic signal could be added to the existing audible acoustic signal being emitted by a speaker which is otherwise used as a standard speaker (for example a speaker in a mobile phone) to match with the optimal size of the first and/or second apertures of the air pump. This way, the speaker will have a dual function of pumping air optimally through the apertures and operating as a standard speaker for emitting for example audible music or voice content.

While the optimal wavelength for the shown configuration is a half wavelength, it is 5 also possible to use an acoustic wave multiple wavelengths long with different configurations.

Figure 7, illustrates an acoustic pump in accordance with a second embodiment of the present invention. In this embodiment, a moveable wall of a piezoelectric transducer 30 defines one wall of an inner chamber 32 defined within the pump housing 34. A single first orifice 36 is formed in a first end wall 38 of the inner chamber 32 that causes fluid to be jetted out when a high pressure is present within the inner chamber 32. Most of this jet is captured by a funnel shaped first aperture 40 formed in a first end wall 41 of the housing 34 adjacent said first end wall 38 of the inner chamber 32 and aligned with said first orifice 36 in the first end all 38 of the inner chamber 32.

In the embodiment of Figure 7, the inner chamber 32 has two small second orifices 42,43 in a second end wall 44 of the inner chamber 32, opposite said first end wall 38. The second orifices 42,43 are located a small distance from the peak of the antinode of the standing wave generated in the inner chamber 32 by the transducer 30. The second orifices 42,43 are offset on either side of a second aperture 45 formed in a second end wall 46 of the housing 34 adjacent said second end 44 of the inner chamber 32.

A diffuser channel 48 extends within the housing 34 around the inner chamber 32, providing fluid communication between a first region defined between the first end wall 41 of the housing 34 and the first end wall 38 of the inner chamber 32 and a second region defined between the second end wall 46 of the housing 34 and the second end wall 44 of the inner chamber.

When a high pressure is present within the inner chamber 32 created by the transducer 30, some fluid exits the second orifices 43,44, but because they are geometrically offset from the second aperture 45, only a small amount of air passes through the second aperture 45. By contrast, the alignment of the first orifice 36 with the antinode of the standing wave within the inner chamber 32 and the alignment of the first orifice 36 with the first aperture 40 in the first end wall 41 of the housing 34 causes a jet of air to be exhausted through the first aperture 40.

When a low pressure is present in the inner chamber 32, fluid is sucked in through the first and second orifices 36,42,43 in the first and second end walls 38,44 of the inner chamber 32. As the pressure drops in the diffuser channel 48 of the housing 34, fluid is sucked in through the first and second apertures 40,45 in the housing.

However, as with the first and second apertures of the first embodiment, the first and second apertures 40,45 are shaped to limit the flow of fluid therethrough is one direction (inwardly in the case of the first aperture 40 and outwardly in the case of the second aperture 45), for example due to the presence of a funnel shaped portion at an inner end of the first aperture and/or a peripheral backflow lip at an outer side of the first aperture 40 and/or at an inner end of the second aperture 45, as shown in Figures 7 and 8.

The shape and geometry of the first and second orifices can also enhance the flow of fluid in one direction.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims

Claims 1. An acoustically driven pump comprising a chamber having opposed first and second side walls and first and second end walls, at least a portion of the first side 5 wall being defined by means for propagating an acoustic wave within said chamber at a predetermined wavelength in order to generate a standing wave between said first and second side walls, one or more apertures being provided each of said first end and second side walls such that pressure differentials within said chamber adjacent said one or more apertures caused by said standing wave causes fluid to to flow through said one or more apertures in a direction substantially parallel to said first side wall.
2. An acoustically driven pump as claimed in claim 1, wherein at least one first aperture is provided in said first end wall and at least one second aperture is provided in said second end wall, wherein said at least one first aperture is adapted to provide a greater flow resistance to the passage of a fluid out of the chamber than to the passage of said fluid into the chamber, and/or said at least one second aperture is adapted to provide a greater flow resistance to the passage of said fluid into the chamber than to the passage of said fluid out of the chamber.
3. An acoustically driven pump as claimed in claim 2, wherein said at least one first aperture has a funnel shape narrowing towards an outer side of said first end wall.
4. An acoustically driven pump as claimed in claim 2 or claim 3, wherein said at 25 least one first aperture is provided with a peripheral backflow lip extending from an outer wall of the chamber.
5. An acoustically driven pump as claimed in any of claims 2 to 4, wherein said at least one second aperture is provided with a peripheral backflow lip extending into 30 the chamber.
6. An acoustically driven pump as claimed in claim 1, wherein said chamber is located within a housing having a first housing end wall adjacent the first end wall of the chamber to define a first region therebetween and a second housing end wall adjacent and the second end wall of the chamber to define a second region therebetween, the housing including at least one diffuser passage extending between said first and second regions, an outlet orifice being provided in said first housing end wall and an inlet orifice being provided in said second housing end wall.
7. An acoustically driven pump as claimed in claim 6, wherein said inlet orifice is adapted to provide a greater flow resistance to the passage of a fluid out of the chamber than to the passage of said fluid into the chamber, and/or said outlet orifice is adapted to provide a greater flow resistance to the passage of said fluid into the chamber than to the passage of said fluid out of the chamber.
8. An acoustically driven pump as claimed in claim 6, wherein the outlet orifice has a funnel shape narrowing towards an outer side of the housing and/or a peripheral 15 backflow lip extending from an outer wall of the housing and/or the inlet orifice is provided with a peripheral backflow lip extending towards the chamber.
9. An acoustically driven pump as claimed in claim 7 or claim 8, wherein the outlet orifice is aligned with an aperture in the first end wall of the chamber, the inlet orifice 20 being offset from the or each aperture in the second wall of the chamber.
10. An acoustically driven pump as claimed in any of claims 6 to 9, wherein the first end wall of the chamber is provided with a single aperture, said single aperture being aligned with the outlet orifice of the housing, the second end wall of the chamber being provided with two apertures, said apertures in said second end wall of the chamber being located on either side of the inlet orifice of the housing.
11. An acoustically driven pump as claimed in any preceding claims, wherein said means for propagating an acoustic wave within said chamber comprises a 30 piezoelectric transducer.
12. An acoustically driven pump as claimed in claim 11, wherein said piezoelectric transducer comprises at least a portion of the first side wall of the chamber.
13. An acoustically driven pump substantially as described herein with reference to the accompanying drawings.