WO2007011553A1

WO2007011553A1 - Asymmetric dual diaphragm pump

Info

Publication number: WO2007011553A1
Application number: PCT/US2006/026528
Authority: WO
Inventors: Eugen I. Cabuz; Tzu-Yu Wang
Original assignee: Honeywell International Inc.
Priority date: 2005-07-14
Filing date: 2006-07-10
Publication date: 2007-01-25
Also published as: EP1902219A1; CN101263302A; US7517201B2; JP2009501297A; US20070014676A1

Abstract

An asymmetric micro pump may be adapted to provide a greater fluid compression between input and output ports of the micro pump, as well as increased flow rate due to higher actuation frequency. In some instances, asymmetric dual diaphragm micro pumps may be combined into assemblies to provide increased pressure build, improved pumping volume, or both, as desired.

Description

ASYMMETRIC DUAL DIAPHRAGM PUMP

Technical Field

[Para 1 ] The present invention relates generally to pumps, and more particularly to dual diaphragm pumps.

Background

[Para 2] Modern consumer, industrial, commercial, aerospace and military systems often depend on reliable pumps for fluid handling. For some applications, such as in some instrumentation, sensing and/or control applications, smaller pump systems are often desirable. Although some important advances have been made in micro pump technology, a need still remains for micro pumps that have improved performance characteristics.

Summary

[Para 3] The present invention generally relates to pumps, and more particularly to dual diaphragm pumps. In some cases, the present invention may provide greater fluid compression between input and output ports of the pump, as well as increased flow rate due to higher actuation frequency, if desired.

[Para 4] In one illustrative embodiment of the present invention, a micro pump is provided that includes a pump chamber having a chamber midline, a first surface and a second surface. The first surface includes a first portion that extends at a first acute angle with respect to the chamber midline. The second surface includes a second portion that extends at a second acute angle with respect to the chamber midline. In some cases, the second angle is less than the first angle, and in some cases may be zero or even negative. The micro pump may include a first diaphragm and a second diaphragm disposed within the chamber. The first diaphragm and the second diaphragm may each have at least one aperture disposed therein. [Para 5] In some instances, the first diaphragm is adapted to be electrostatically actuated toward the first surface and/or the second surface, and the second diaphragm is adapted to be electrostatically actuated toward the second surface and/or the first surface. In some cases, the first diaphragm and the second diaphragm are adapted to return to a position proximate the chamber midline by elastic restoring forces, but this is not required in all embodiments. At least one aperture disposed within the first diaphragm may be mis-aligned with the at least one aperture disposed within the second diaphragm when the first and second diaphragms are positioned proximate to one another.

[Para 6] In some cases, the first surface can include a first port. The first diaphragm may be adapted to be electrostatically actuated to a position adjacent to the first surface to seal or substantially seal the first port. Likewise, the second surface can include a second port, and the second diaphragm may be adapted to be electrostatically actuated to a position adjacent the second surface to seal or substantially seal the second port.

[Para 7] In some instances, the first diaphragm and the second diaphragm are adapted so that they may be independently electrostatically actuated. For example, the first diaphragm may be adapted such that it can be independently electrostatically actuated to a position adjacent the first surface, so that the first diaphragm seals or substantially seals the first port, or adjacent the second surface. Likewise, the second diaphragm may be adapted such that it can be independently electrostatically actuated into a position adjacent the second surface so that the second diaphragm seals or substantially seals the second port, or adjacent the first surface. In some cases, vertical and/or horizontal stacks of such micro pumps may be provided to increase pumping compression or capacity, and in some cases, improve reliability, as desired.

[Para 8] The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures, Detailed Description and Examples which follow more particularly exemplify these embodiments.

Brief Description of the Figures

[Para 9] The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

[Para 10] Figure 1 is an exploded cross-sectional view of a micro pump chamber in accordance with an embodiment of the present invention;

[Para 1 1 ] Figure 2 is an exploded cross-sectional view of an asymmetric dual diaphragm micro pump in accordance with an embodiment of the present invention;

[Para 12] Figure 3 is an exploded cross-sectional view of an asymmetric dual diaphragm micro pump in accordance with an embodiment of the present invention;

[Para 13] Figures 4 through 9 schematically illustrate operation of the micro pump of Figure 2;

[Para 14] Figure 10 is a cross-sectional view of a vertical stack micro pump array deploying two asymmetric dual diaphragm micro pumps in accordance with an embodiment of the present invention;

[Para 1 5] Figure 1 1 is a cross-sectional view of a vertical stack micro pump array deploying three asymmetric dual diaphragm micro pumps in accordance with an embodiment of the present invention; and

[Para 16] Figure 1 2 is a diagrammatic illustration of a massively parallel micro pump array in accordance with an embodiment of the present invention.

[Para 1 7] While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Detailed Description

[Para 18]The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. [Para 19] Figure 1 is an exploded view of a micro pump chamber 10 that includes an upper section 1 2 and a lower section 14. In the description that follows, the designations of upper and lower are arbitrary, and are made merely for ease of discussion. In some instances, micro pump chamber 10 may be circular in shape if viewed from above or below. Other shapes are of course contemplated as well.

[Para 20] A chamber midline 16 can be seen as extending between upper section 12 and lower section 14. The term "chamber midline" is not intended to imply that it extends exactly in the middle of the chambers, but rather that it simply divides the chamber into two parts. It should be noted that the spacing between elements in Figure 1 has been greatly exaggerated for clarity. When upper section 1 2 and lower section 14 are positioned next to each other, and in the illustrative embodiment shown in Figure 1 , it can be seen that chamber midline 16 will intersect the junction between upper section 1 2 and lower section 14.

[Para 21 ] Upper section 12 has a surface 1 8 that includes a portion 20 that forms an acute angle a with chamber midline 16. Similarly, lower section 14 has a surface 22 that includes a portion 24 that forms an angle β with chamber midline 16. In some instances, angle β may be less than angle ex. In some cases, angle β may be at least about 0.25 degrees less than angle a.

[Para 22] Angle a may be as large as desired to accomplish desired pumping characteristics and may be as large as about 45 degrees. In some particular instances, angle a. may be, for example, in the range of about 0.5 degrees to about 5.0 degrees, while angle β may be in the range of about 0 to about 4.75 degrees. In some instances, angle β may be less than about 2.0 degrees and in some cases, and as illustrated with respect to Figure 3, may be equal to about zero, or even negative if desired.

[Para 23] It can be noted that setting angle β to be less than angle <x can reduce the working volume of, or the total space within micro pump chamber 10 (i.e. between upper section 1 2 and lower section 14). However, in some instances, reducing angle β with respect to angle a can provide improvements in some performance parameters. For example, by reducing angle β with respect to angle a, pumping frequency may be increased. Alternatively, or in addition, reducing angle β with respect to angle α may help increase the pressure differential that can be achieved across micro pump chamber 10. [Para 24] In the illustrative embodiment, upper section 12 includes a port 26 while lower section 14 includes a port 28. It should be noted that while micro pump chamber 1 0 is not symmetric with respect to opposing sides of chamber midline 16 (i.e. upper section 12 is not symmetric to lower section 14), micro pump chamber 10 can in some embodiments be symmetric in the left-right direction. In other words, in the illustrative embodiment of Figure 1 , the right hand portion of upper section 1 2 (without reference numbers) may be a mirror image of the left hand portion of upper section 1 2 (with reference numbers), but this is not required. Similarly, right hand portion of lower section 14 may be a mirror image of the left hand portion of lower section 14, but this is also not required.

[Para 25] In some instances, micro pump chamber 10 including upper section 1 2 and lower section 14 may be formed from any suitable semi-rigid or rigid material, such as plastic, ceramic, silicon, etc. For example, and in some embodiments, micro pump chamber 10 may be constructed by molding a high temperature plastic such as ULTEM™ (available from General Electric Company, Pittsfield, Mass.), CELAZOLE™ (available from Hoechst-Celanese Corporation, Summit, NJ.), KETRON™ (available from Polymer Corporation, Reading, Pa.), or some other suitable material. [Para 26] Figure 2 is an exploded view of a micro pump 30 employing micro pump chamber 10 (Figure 1 ). Chamber midline 16 (Figure 1 ) has been excised from this Figure to better illustrate an upper diaphragm 32 and a lower diaphragm 34. In the illustrative embodiment, upper diaphragm 32 includes one or more upper apertures 36 and lower diaphragm 34 includes one or more lower apertures 38. As can be seen in Figure 2, upper apertures 36 may be laterally offset from lower apertures 38.

[Para 27] In some instances, upper apertures 36 may be aligned within upper diaphragm 32 about a circle of a first radius while lower apertures 38 may be aligned within lower diaphragm 34 about a circle of a second radius that is different from the first radius, with both radii having a common center point. In this configuration, the upper apertures 36 are misaligned with the lower apertures 38, and when the upper diaphragm 32 and the lower diaphragm 34 are situated directly adjacent to one another (e.g. in contact), the upper diaphragm 32 may seal or substantially seal the lower apertures 38 and the lower diaphragm 34 may seal or substantially seal the upper apertures 36. [Para 28] In some instances, the material used to make the upper diaphragm 32 and the lower diaphragm 34 may have elastic, resilient, flexible or other elastomeric properties, but this is not required in all embodiments. In some cases, upper diaphragm 32 and lower diaphragm 34 may be made from a generally compliant material. For example, upper diaphragm 32 and lower diaphragm 34 may be made from a polymer such as KAPTON™ (available from E. I. du Pont de Nemours & Co., Wilmington, Del.), KALADEX™ (available from ICI Films, Wilmington, Del.), MYLAR™ (available from E. I. du Pont de Nemours & Co., Wilmington, Del.), ULTEM™ (available from General Electric Company, Pittsfield, Mass.) or any other suitable material as desired.

[Para 29] As will be discussed in greater detail with respect to Figures 4 through 9, upper diaphragm 32 and lower diaphragm 34 may be electrostatically actuated through a variety of positions. Upper diaphragm 32 can be electrostatically actuated to a position in which the upper diaphragm is disposed next to surface 1 8 such that the upper diaphragm seals or substantially seals port 26. Likewise, the lower diaphragm 34 can be electrostatically actuated to a position in which lower diaphragm 34 is disposed next to surface 22 such that the lower diaphragm seals or substantially seals port 28. In some cases, the upper diaphragm 32 and the lower diaphragm 34 may be independently electrostatically actuated. For example, the upper diaphragm 32 and the lower diaphragm 34 may move in opposite directions and/or in unison, in some cases, one of the upper diaphragm 32 or lower diaphragm 34 may be electrostatically moved while the other remains stationary.

[Para 30] In order to provide for electrostatic actuation of upper diaphragm 32 and lower diaphragm 34, it will be recognized that upper diaphragm 32, lower diaphragm 34, surface 1 8 and surface 22 may each include a corresponding electrode. Electrodes may be formed of any suitable material, using any suitable technique. By applying voltages between appropriate electrodes, upper diaphragm 32 and lower diaphragm 34 may be moved as desired via electrostatic forces. In some instances, each of the electrodes (not illustrated) may include one or more dielectric layers, either under or above each electrode, to help prevent electrical shorts between the electrodes, particularly when the corresponding components engage one another. [Para 31 ] Figure 3 is an exploded view of a micro pump 40 including upper section 12 as discussed with respect to Figure 2 and a lower section 42. Upper diaphragm 32 and lower diaphragm 34 function and are constructed as discussed previously. In this illustrative embodiment, angle β is shown to be about zero degrees, and thus lower section 42 includes a surface 44 that is disposed at least substantially parallel with chamber midline 16 (Figure 1 ). In some cases, the lower diaphragm 34 may not need to be electrostatically pulled down toward surface 44, as elastic restoring forces may provide this function. However, in some embodiments, the lower diaphragm 34 is electrostatically pulled down toward surface 44. [Para 32] Figures 4 through 9 are diagrammatic cross-sections showing an illustrative pumping cycle employing micro pump 30 (Figure 2). In particular, these Figures illustrate a pumping sequence where the inlet is on the bottom, and the outlet is on the top. An opposite configuration is equally appropriate since the illustrative micro pump may be completely reversible. As referenced previously, and in some illustrative embodiments, upper diaphragm 32 and lower diaphragm 34 may be electrostatically actuated between various positions. As they move, upper diaphragm 32 and lower diaphragm 34 may be considered as defining an upper volume 48, a lower volume 50 and a middle volume 52.

[Para 33] It should be noted that the spacing between individual components has been exaggerated for clarity in Figures 4 through 9. In many cases, upper diaphragm 32 and lower diaphragm 34 would actually be in physical contact when moving in unison, as shown, for example, in Figures 4, 5 and 6.

[Para 34] Upper volume 48 is formed between portion 20 of surface 1 8 and upper diaphragm 32, lower volume 50 is formed between lower diaphragm 34 and portion 24 of surface 22, and middle volume 52 is formed between upper diaphragm 32 and lower diaphragm 34. It will be recognized that at particular pumping cycle stages, one or more of upper volume 48, lower volume 50 and middle volume 52 may essentially disappear (i.e. become zero or substantially zero), depending on the relative positions of upper diaphragm 32 and lower diaphragm 34.

[Para 35] In Figure 4, upper diaphragm 32 and lower diaphragm 34 have both been electrostatically pulled down, thereby sealing port 28. At this point, fluid (e.g. gas or liquid) is assumed to be contained within upper volume 48, while lower volume 50 and middle volume 52 are essentially eliminated by the position of upper diaphragm 32 and lower diaphragm 34. As can be seen, upper apertures 36 and lower apertures 38 do not align with each other or with either of port 26 or port 28, in order to affect desired seals during each cycle. [Para 36] Figure 5 illustrates initiation of the pump stroke by simultaneously electrostatically pulling upper diaphragm 32 and lower diaphragm 34 towards the top, thus pushing the fluid that is contained within upper volume 48 through port 26. In the illustrative embodiment, this may be accomplished by providing appropriate voltages between the electrodes on portion 20 of surface 18 and the upper diaphragm 32 and/or lower diaphragm 34. In some cases, elastic restoring forces may supplement the movement of the upper diaphragm 32 and lower diaphragm 34 to the position shown in Figure 5, or may be used exclusively. Figure 6 illustrates completion of this pump stroke, with both upper diaphragm 32 and lower diaphragm 34 electrostatically pulled up to seal port 26. At this point, all of the fluid that was in upper volume 48 has been pushed out and expelled through port 26. During this same stroke new fluid is drawn in to lower volume 50 via port 28.

[Para 37] In Figure 7, upper diaphragm 32 remains in sealing relationship with port 26 while lower diaphragm 34 is electrostatically and/or elastically pulled down, thereby causing the fluid in lower volume 50 to transfer into middle chamber 52 via lower apertures 38 (Figure 2) within lower diaphragm 34. Figure 8 illustrates the orientation of lower diaphragm 34 completely pulled down electrostatically to seal port 28 while upper diaphragm 32 remains in position sealing port 26. Finally, Figure 9 illustrates the midpoint of movement of upper diaphragm 32 down toward lower diaphragm 34, wherein fluid may be pulled from middle volume 52 into upper volume 48. Eventually, the upper diaphragm 32 is pulled down until it is adjacent to the lower diaphragm 34, as shown in Figure 4, thus completing the pump cycle. The above-described pumping cycle may be repeated to pump more fluid from port 28 to port 26. [Para 38] In some illustrative embodiments, micro pumps such as micro pump 30 or micro pump 40 may be assembled into micro pump arrays. By arranging micro pumps 30 or micro pumps 40 in series, i.e. the output of a first micro pump 30 or micro pump 40 may be provided to an input of a second micro pump 30 or micro pump 40. This may create a greater pressure build-up across the micro pump assembly. By arranging micro pumps 30 or micro pumps 40 in parallel, greater pumping volume may be achieved. In some instances, two or more micro pumps 30 or micro pumps 40 may be arranged in series, and a number of the series of micro pumps 30 or micro pumps 40 may then be arranged in parallel to provide a two dimensional pumping array that provides both an improved pressure differential as well as greater pumping volume. Figures 10 through 14 show particular examples of some illustrative micro pump arrays. [Para 39] Figure 10 illustrates a micro pump array 54 that includes an upper micro pump 56 and a lower micro pump 58. It should be noted that designations of upper and lower are arbitrary, as micro pump array 54 can be inverted. In the illustrative embodiment, upper micro pump 56 and lower micro pump 58 may be constructed and function as discussed previously with respect to micro pump 40 (Figure 3). Upper micro pump 56 includes an inlet 60 and an outlet 62. Lower micro pump 58 includes an inlet 64 and an outlet 66, with the inlet in fluid communication with the outlet 62 of upper micro pump 56. [Para 40] Upper micro pump 56 includes an upper diaphragm 68 and a lower diaphragm 70, as discussed previously with respect to upper diaphragm 32 and lower diaphragm 34 (Figures 2 and 3). Similarly, lower micro pump 58 includes an upper diaphragm 72 and a lower diaphragm 74. Upper diaphragm 68 includes several apertures 76, and lower diaphragm includes several other apertures 78 that are misaligned with apertures 76 of the upper diaphragm 68. Similarly, upper diaphragm 72 includes several apertures 80, while lower diaphragm 74 includes several misaligned apertures 82. [Para 41 ] During use, fluid enters inlet 60 and is pumped through to outlet 62 as discussed previously with respect to Figure 3. The fluid then enters inlet 64 and is pumped through to outlet 66. The fluid pressure increases between inlet 60 and outlet 62, and then increases again between inlet 64 and outlet 66. The total pressure differential across the pump array may be the sum of these fluid pressure increases.

[Para 42] Figure 1 1 illustrates a micro pump array 84 that includes an upper micro pump 86, an intermediate micro pump 88 and a lower micro pump 90. Upper micro pump 86 has an inlet 92 and an outlet 94. Intermediate micro pump 88 has an inlet 96 and an outlet 98, where the inlet 96 is in fluid communication with outlet 94 of the upper micro pump 86. Lower micro pump 90 has an inlet 100 and an outlet 102, wherein the inlet 100 is in fluid communication with the outlet 98 of the intermediate micro pump 88. Construction and function of upper micro pump 86, intermediate micro pump 88 and lower micro pump 90 may be the same as described with respect to Figure 10 and thus is not further discussed in detail here. [Para 43] During use, fluid enters inlet 92 and is pumped through to outlet 94 as discussed previously with respect to Figure 10. The fluid then enters inlet 96 and is pumped through to outlet 98. Fluid then enters inlet 100 and is pumped through to outlet 102. As discussed, the fluid pressure may increase as the fluid passes through each of upper micro pump 86, intermediate micro pump 88 and lower micro pump 90. It is contemplated that any number of micro pumps may be stacked in a similar manner to achieve a desired pressure increase. [Para 44] Figure 12 illustrates a micro pump array 144 that includes a number of pumps (such as micro pump 40 of Figure 3) arranged in series, with two or more series of pumps arranged in parallel. In the illustrative embodiment, micro pump array 144 includes a first micro pump series 146, a second micro pump series 148, a second-to-last micro pump series 1 50 and a last micro pump series 1 52. Each of first micro pump series 146, second micro pump series 148, second-to- last micro pump series 150, last micro pump series 1 52, and each of the intermediate micro pump series (not shown) function as discussed with respect to micro pump array 1 30 (Figure 1 1 ). By placing a number of micro pump series (or arrays) in parallel, fluid pumping capacity may be increased. Also, by placing a number of micro pumps in parallel, the reliability of the pumping system may be increased because if one or more pump cell fails, others may provide compensation, and/or other unused (redundant) micro-pumps may be activated.

[Para 45] The invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the invention can be applicable will be readily apparent to those of skill in the art upon review of the instant specification.

Claims

What is claimed is:

1. A micro pump comprising: a chamber having a chamber midline; a first surface including a first portion extending at a first acute angle with respect to the chamber midline; a second surface opposite the first surface, the second surface including a second portion extending at a second acute angle with respect to the chamber midline; a first diaphragm disposed within the chamber, at least one first aperture disposed within the first diaphragm; and a second diaphragm disposed within the chamber, at least one second aperture disposed with the second diaphragm; wherein the second angle is less than the first angle.

2. The micro pump of claim 1 , wherein each of the first diaphragm and the second diaphragm are adapted to be electrostatically actuated between a position proximate the first surface and a position proximate the second surface.

3. The micro pump of claim 1 , wherein when the first diaphragm and the second diaphragm are situated adjacent to one another, the at least one first aperture disposed within the first diaphragm is/are not aligned with the at least one second aperture disposed within the second diaphragm.

4. The micro pump of claim 1 , wherein the first surface further comprises a first port, and the first diaphragm is adapted to be electrostatically actuated to a position in which the first diaphragm seals the first port.

5. The micro pump of claim 1 , wherein the second surface further comprises a second port, and the second diaphragm is adapted to be electrostatically actuated to a position in which the second diaphragm seals the second port.

6. The micro pump of claim 1 , wherein the second angle is at least about 0.25 degrees less than the first angle.

7. The micro pump of claim 1 , wherein the first angle is in the range of about 0.5 to about 5.0 degrees.

8. The micro pump of claim 1 , wherein the second angle is less than about 4.75 degrees.

9. The micro pump of claim 1 , wherein the second surface is at least substantially parallel with the chamber midline.

10. A micro pump comprising: a micro pump chamber having a lower first surface and a non- parallel upper second surface, a first port disposed within the lower first surface and a second port disposed within the second upper surface; and a dual diaphragm disposed within the micro pump chamber, the dual diaphragm comprising a first diaphragm having at least one first apertures and a second diaphragm having at least one second apertures, wherein none of the at least one second apertures is/are aligned with the any of the at least one first apertures when the first diaphragm is situated adjacent to the second diaphragm, and wherein the first lower surface of the micro pump chamber extends parallel or substantially parallel to the first diaphragm when the first diaphragm is un-activated and at rest.

1 1 . The micro pump of claim 1 0, wherein the first diaphragm and the second diaphragm are adapted to be independently electrostatically actuated within the micro pump chamber.

12. The micro pump of claim 1 1 , wherein the first diaphragm is adapted to be electrostatically actuated into a position in which the first diaphragm seals the first port.

1 3. The micro pump of claim 1 1 , wherein the second diaphragm is adapted to be electrostatically actuated into a position in which the second diaphragm seals the second port.

14. A vertical stack micro pump array comprising: a first dual diaphragm chamber comprising: a first angled upper surface having a first input port; an opposing first angled lower surface having a first output port, wherein the first angled upper surface is situated at a different relative angle than the opposing first angled lower surface; and a first dual diaphragm comprising a first upper diaphragm and a first lower diaphragm; and a second dual diaphragm chamber comprising: a second angled upper surface having a second input port; an opposing second angled lower surface having a second output port, wherein the second angled upper surface is situated at a different relative angle than the opposing second angled lower surface; and a second dual diaphragm comprising a second upper diaphragm and a second lower diaphragm; wherein the second input port is in fluid communication with the first output port.

1 5. The vertical stack micro pump array of claim 14, wherein the first dual diaphragm comprises a first upper diaphragm having an upper first plurality of apertures and a first lower diaphragm having a lower first plurality of apertures misaligned with the upper first plurality of apertures.

16. The vertical stack micro pump array of claim 14, wherein the second dual diaphragm comprises a second upper diaphragm having an upper second plurality of apertures and a second lower diaphragm having a lower second plurality of apertures misaligned with the upper second plurality of apertures.

1 7. The vertical stack micro pump array of claim 14, further comprising: a third dual diaphragm chamber comprising: a third angled upper surface having a third input port; an opposing third angled lower surface having a third output port, wherein the third angled upper surface is situated at a different relative angle than the opposing third angled lower surface; and a third dual diaphragm comprising a third upper diaphragm and a third lower diaphragm; wherein the third input port is in fluid communication with the second output port.

1 8. The vertical stack micro pump array of claim 14 wherein the first dual diaphragm chamber includes a chamber midline, and the first angled upper surface is situated at a first angle relative to the chamber midline and the opposing first angled lower surface is situated at a second angle relative to the chamber midline, wherein the first angle is different from the second angle.

19. The vertical stack micro pump of claim 1 8 wherein the second angle is zero or substantially zero.

20. The vertical stack micro pump array of claim 14, further comprising another vertical stack micro pump situated in a parallel relationship.