Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLUID DISC PUMP
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The illustrative embodiments of the invention relate generally to a
pump for fluid
and, more specifically, to a pump in which the pumping cavity is substantially
a disc-shaped,
cylindrical cavity having substantially circular end walls and a side wall.
2. Description of Related Art
[0002] The generation of high amplitude pressure oscillations in closed
cavities has
received significant attention in the fields of thermo-acoustics and pump type
compressors.
Recent developments in non-linear acoustics have allowed the generation of
pressure waves with
higher amplitudes than previously thought possible.
[0003] It is known to use acoustic resonance to achieve fluid pumping from
defined
inlets and outlets. This can be achieved using a cylindrical cavity with an
acoustic driver at one
end, which drives an acoustic standing wave. In such a cylindrical cavity, the
acoustic pressure
wave has limited amplitude. Varying cross-section cavities, such as cone, horn-
cone, bulb have
been used to achieve high amplitude pressure oscillations thereby
significantly increasing the
pumping effect. In such high amplitude waves the non-linear mechanisms with
energy
dissipation have been suppressed. However, high amplitude acoustic resonance
has not been
employed within disc-shaped cavities in which radial pressure oscillations are
excited until
recently. International Patent Application No. PCT/GB2006/001487, published as
WO
2006/111775 (the '487 Application), discloses a pump having a substantially
disc-shaped cavity
with a high aspect ratio, i.e., the ratio of the radius of the cavity to the
height of the cavity.
[0004] Such a pump has a substantially cylindrical cavity comprising a side
wall closed
at each end by end walls. The pump also comprises an actuator that drives
either one of the end
walls to oscillate in a direction substantially perpendicular to the surface
of the driven end wall.
The spatial profile of the motion of the driven end wall is described as being
matched to the
spatial profile of the fluid pressure oscillations within the cavity, a state
described herein as
mode-matching. When the pump is mode-matched, work done by the actuator on the
fluid in the
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cavity adds constructively across the driven end wall surface, thereby
enhancing the amplitude of
the pressure oscillation in the cavity and delivering high pump efficiency. In
a pump which is
not mode-matched there may be areas of the end wall wherein the work done by
the end wall on
the fluid reduces rather than enhances the amplitude of the fluid pressure
oscillation in the fluid
within the cavity. Thus, the useful work done by the actuator on the fluid is
reduced and the
pump becomes less efficient. The efficiency of a mode-matched pump is
dependent upon the
interface between the driven end wall and the side wall. It is desirable to
maintain the efficiency
of such pump by structuring the interface so that it does not decrease or
dampen the motion of
the driven end wall thereby mitigating any reduction in the amplitude of the
fluid pressure
oscillations within the cavity.
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SUMMARY
[0005] According to one embodiment of the invention, the actuator of the pump
described above causes an oscillatory motion of the driven end wall
("displacement oscillations")
in a direction substantially perpendicular to the end wall or substantially
parallel to the
longitudinal axis of the cylindrical cavity, referred to hereinafter as "axial
oscillations" of the
driven end wall within the cavity. The axial oscillations of the driven end
wall generate
substantially proportional "pressure oscillations" of fluid within the cavity
creating a radial
pressure distribution approximating that of a Bessel function of the first
kind as described in the
'487 Application which is incorporated by reference herein, such oscillations
referred to
hereinafter as "radial oscillations" of the fluid pressure within the cavity.
A portion of the driven
end wall between the actuator and the side wall provides an interface with the
side wall of the
pump that decreases dampening of the displacement oscillations to mitigate any
reduction of the
pressure oscillations within the cavity, that portion being referred to
hereinafter as an "isolator."
The illustrative embodiments of the isolator are operatively associated with
the peripheral
portion of the driven end wall to reduce dampening of the displacement
oscillations.
[0006] According to another embodiment of the invention, a pump comprises a
pump
body having a substantially cylindrical shape defining a cavity formed by a
side wall closed at
both ends by substantially circular end walls, at least one of the end walls
being a driven end
wall having a central portion and a peripheral portion adjacent the side wall,
wherein the cavity
contains a fluid when in use. The pump further comprises an actuator
operatively associated
with the central portion of the driven end wall to cause an oscillatory motion
of the driven end
wall in a direction substantially perpendicular thereto with a maximum
amplitude at about the
centre of the driven end wall, thereby generating displacement oscillations of
the driven end wall
when in use. The pump further comprises an isolator operatively associated
with the peripheral
portion of the driven end wall to reduce dampening of the displacement
oscillations caused by
the end wall's connection to the side wall of the cavity. The pump further
comprises a first
aperture disposed at about the centre of one of the end walls, and a second
aperture disposed at
any other location in the pump body, whereby the displacement oscillations
generate radial
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oscillations of fluid pressure within the cavity of said pump body causing
fluid flow through said
apertures.
[0007] Other objects, features, and advantages of the illustrative embodiments
will
become apparent with reference to the drawings and detailed description that
follow.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Figure 1A shows a schematic cross-section view of a first pump
according to an
illustrative embodiment of the inventions that provide a positive pressure, a
graph of the
displacement oscillations of the driven end wall of the pump, and a graph of
the pressure
oscillations within the cavity of pump.
[0009] Figure 1B shows a schematic top view of the first pump of Figure 1A.
[0010] Figure 2A shows a schematic cross-section view of a valve for use with
the
pumps according to the illustrative embodiments of the invention.
[0011] Figures 2A(1) and 2A(2) show a section of the valve of Figure 2A in
operation.
[0012] Figure 2B shows a schematic top view of the valve of Figure 2A.
[0013] Figure 3 shows a schematic cross-section view of a second pump
according to an
illustrative embodiment of the inventions that provides a negative pressure.
[0014] Figure 4 shows a schematic cross-section view of a third pump according
to an
illustrative embodiment of the inventions having a frusto-conical base.
[0015] Figure 5 shows a schematic cross-section view of a fourth pump
according to
another illustrative embodiment of the invention including two actuators.
[0016] Figure 6 shows an exploded schematic section of the edge of the pump of
Figures
lA and 1B illustrating a first embodiment of an isolator and the corresponding
graphs of the
displacement and pressure oscillations within the cavity.
[0017] Figures 7A and 7B show schematic cross-section views of the pump of
Figure 3
illustrating different embodiments of the isolator of Figure 3.
[0018] Figure 8 shows a schematic cross-section view of the pump of Figure 1
illustrating another embodiment of an isolator.
[0019] Figure 9 shows a schematic cross-section view of the pump of Figure 1
illustrating yet another embodiment of an isolator.
[0020] Figure 10 shows a schematic cross-section view of the pump of Figure 1
illustrating yet another embodiment of an isolator and the corresponding
graphs of the
displacement and pressure oscillations within the cavity.
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DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] In the following detailed description of several illustrative
embodiments,
reference is made to the accompanying drawings that form a part hereof, and in
which is shown
by way of illustration specific preferred embodiments in which the invention
may be practiced.
These embodiments are described in sufficient detail to enable those skilled
in the art to practice
the invention, and it is understood that other embodiments may be utilized and
that logical
structural, mechanical, electrical, and chemical changes may be made without
departing from the
spirit or scope of the invention. To avoid detail not necessary to enable
those skilled in the art to
practice the embodiments described herein, the description may omit certain
information known
to those skilled in the art. The following detailed description is, therefore,
not to be taken in a
limiting sense, and the scope of the illustrative embodiments are defined only
by the appended
claims.
[0022] Figure lA is a schematic cross-section view of a pump 10 according to
an
illustrative embodiment of the invention. Referring also to Figure 1B, pump 10
comprises a
pump body having a substantially cylindrical shape including a cylindrical
wall 19 closed at one
end by a base 18 and closed at the other end by an end plate 17 and a ring-
shaped isolator 30
disposed between the end plate 17 and the other end of the cylindrical wall 19
of the pump body.
The cylindrical wall 19 and base 18 may be a single component comprising the
pump body and
may be mounted to other components or systems. The internal surfaces of the
cylindrical wall
19, the base 18, the end plate 17, and the isolator 30 form a cavity 11 within
the pump 10
wherein the cavity 11 comprises a side wall 14 closed at both ends by end
walls 12 and 13. The
end wall 13 is the internal surface of the base 18 and the side wall 14 is the
inside surface of the
cylindrical wall 19. The end wall 12 comprises a central portion corresponding
to the inside
surface of the end plate 17 and a peripheral portion corresponding to the
inside surface of the
isolator 30. Although the cavity 11 is substantially circular in shape, the
cavity 11 may also be
elliptical or other shape. The base 18 and cylindrical wall 19 of the pump
body may be formed
from any suitable rigid material including, without limitation, metal,
ceramic, glass, or plastic.
[0023] The pump 10 also comprises a piezoelectric disc 20 operatively
connected to the
end plate 17 to foul' an actuator 40 that is operatively associated with the
central portion of the
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end wall 12 via the end plate 17. The piezoelectric disc 20 is not required to
be formed of a
piezoelectric material, but may be formed of any electrically active material
such as, for
example, an electrostrictive or magnetostrictive material. The end plate 17
preferably possesses
a bending stiffness similar to the piezoelectric disc 20 and may be formed of
an electrically
inactive material such as a metal or ceramic. When the piezoelectric disc 20
is excited by an
oscillating electrical current, the piezoelectric disc 20 attempts to expand
and contract in a radial
direction relative to the longitudinal axis of the cavity 11 causing the end
plate 17 to bend,
thereby inducing an axial deflection of the end wall 12 in a direction
substantially perpendicular
to the end wall 12. The end plate 17 alternatively may also be formed from an
electrically active
material such as, for example, a piezoelectric, magnetostrictive, or
electrostrictive material. In
another embodiment, the piezoelectric disc 20 may be replaced by a device in a
force-
transmitting relation with the end wall 12 such as, for example, a mechanical,
magnetic or
electrostatic device, wherein the end wall 12 may be formed as an electrically
inactive or passive
layer of material driven into oscillation by such device (not shown) in the
same manner as
described above.
100241 The pump 10 further comprises at least two apertures extending from the
cavity
11 to the outside of the pump 10, wherein at least a first one of the
apertures may contain a valve
to control the flow of fluid through the aperture. Although the aperture
containing a valve may
be located at any position in the cavity 11 where the actuator 40 generates a
pressure differential
as described below in more detail, one preferred embodiment of the pump 10
comprises an
aperture with a valve located at approximately the centre of either of the end
walls 12,13. The
pump 10 shown in Figures 1 A and 1B comprises a primary aperture 16 extending
from the cavity
11 through the base 18 of the pump body at about the centre of the end wall 13
and containing a
valve 46. The valve 46 is mounted within the primary aperture 16 and permits
the flow of fluid
in one direction as indicated by the arrow so that it functions as an outlet
for the pump 10. The
second aperture 15 may be located at any position within the cavity 11 other
than the location of
the aperture 16 with the valve 46. In one preferred embodiment of the pump 10,
the second
aperture is disposed between the centre of either one of the end walls 12,13
and the side wall 14.
The embodiment of the pump 10 shown in Figures 1A and 1B comprises two
secondary
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apertures 15 extending from the cavity 11 through the actuator 40 that are
disposed between the
centre of the end wall 12 and the side wall 14. Although the secondary
apertures 15 are not
valved in this embodiment of the pump 10, they may also be valved to improve
performance if
necessary. In this embodiment of the pump 10, the primary aperture 16 is
valved so that the fluid
is drawn into the cavity 11 of the pump 10 through the secondary apertures 15
and pumped out
of the cavity 11 through the primary aperture 16 as indicated by the arrows to
provide a positive
pressure at the primary aperture 16.
[0025] Referring to Figure 3, the pump 10 of Figure 1 is shown with an
alternative
configuration of the primary aperture 16. More specifically, the valve 46' in
the primary
aperture 16' is reversed so that the fluid is drawn into the cavity 11 through
the primary aperture
16' and expelled out of the cavity 11 through the secondary apertures 15 as
indicated by the
arrows, thereby providing suction or a source of reduced pressure at the
primary aperture 16'.
The teiin "reduced pressure" as used herein generally refers to a pressure
less than the ambient
pressure where the pump 10 is located. Although the term "vacuum" and
"negative pressure"
may be used to describe the reduced pressure, the actual pressure reduction
may be significantly
less than the pressure reduction normally associated with a complete vacuum.
The pressure is
"negative" in the sense that it is a gauge pressure, i.e., the pressure is
reduced below ambient
atmospheric pressure. Unless otherwise indicated, values of pressure stated
herein are gauge
pressures. References to increases in reduced pressure typically refer to a
decrease in absolute
pressure, while decreases in reduced pressure typically refer to an increase
in absolute pressure.
[0026] The valves 46 and 46' allow fluid to flow through in substantially one
direction as
described above. The valves 46 and 46' may be a ball valve, a diaphragm valve,
a swing valve, a
duck-bill valve, a clapper valve, a lift valve, or any other type of check
valve or any other valve
that allows fluid to flow substantially in only one direction. Some valve
types may regulate fluid
flow by switching between an open and closed position. For such valves to
operate at the high
frequencies generated by the actuator 40, the valves 46 and 46' must have an
extremely fast
response time such that they are able to open and close on a timescale
significantly shorter than
the timescale of the pressure variation. One embodiment of the valves 46 and
46' achieve this by
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employing an extremely light flap valve which has low inertia and consequently
is able to move
rapidly in response to changes in relative pressure across the valve
structure.
[0027] Referring more specifically to Figure 2A, a schematic cross-section
view of one
embodiment of a flap valve 50 is shown mounted within the aperture 16 (or
16'). The flap valve
50 comprises a flap 51 disposed between a retention plate 52 and a sealing
plate 53 and biased
against the sealing plate 53 in a "closed" position which seals the flap valve
50 when not in use,
i.e., the flap valve 50 is normally closed. The valve 50 is mounted within the
aperture 16 so that
the upper surface of the retention plate 52 is preferably flush with the end
wall 13 to maintain the
resonant quality of the cavity 11. The retention plate 52 and the sealing
plate 53 both have vent
holes 54 and 55 respectively that extend from one side of the plate to the
other as represented by
the dashed and solid circles, respectively, in Figure 2B which is a top view
of the flap valve 50
of Figure 2A. The flap 51 also has vent holes 56 which are generally aligned
with the vent holes
54 of the retention plate 52 to provide a passage through which fluid may flow
as indicated by
the dashed arrows in Figure 2A(1). However, as can be seen in Figures 2A and
2B, the vent
holes 54 of the retention plate 52 and the vent holes 56 of the flap 51 are
not in alignment with
the vent holes 55 of the sealing plate 53 which are blocked by the flap 51
when in the "closed"
position as shown so that fluid cannot flow through the flap valve 50.
[0028] The operation of the flap valve 50 is a function of the change in
direction of the
differential pressure (AP) of the fluid across the flap valve 50. In Figure
2A, the differential
pressure has been assigned a negative value (-AP) as indicated by the downward
pointing arrow.
This negative differential pressure (-AP) drives the flap 51 into the fully
closed position as
described above wherein the flap 51 is sealed against the sealing plate 53 to
block the vent holes
55 and prevent the flow of fluid through the flap valve 50. When the
differential pressure across
the flap valve 50 reverses to become a positive differential pressure (+AP) as
indicated by the
upward pointing arrow in Figure 2A(1), the biased flap 51 is motivated away
from the sealing
plate 53 against the retention plate 52 into an "open" position. In this
position, the movement of
the flap 51 unblocks the vent holes 55 of the sealing plate 53 so that fluid
is permitted to flow
through vent holes 55 and then the aligned vent holes 56 of the flap 51 and
vent holes 54 of the
retention plate 52 as indicated by the dashed arrows. When the differential
pressure changes
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back to a negative differential pressure (-AP) as indicated by the downward
pointing arrow in
Figure 2A(2), fluid begins flowing in the opposite direction through the flap
valve 50 as
indicated by the dashed arrows which forces the flap 51 back toward the closed
position shown
in Figure 2A. Thus, the changing differential pressure cycles the flap valve
50 between closed
and open positions to block the flow of fluid after closing the flap 51 when
the differential
pressure changes from a positive to a negative value. It should be understood
that flap 51 could
be biased against the retention plate 52 in an "open" position when the flap
valve 50 is not in use
depending upon the application of the flap valve 50, i.e., the flap valve
would then be normally
open.
[00291 Referring now to Figure 4, a pump 70 according to another illustrative
embodiment of the invention is shown. The pump 70 is substantially similar to
the pump 10 of
Figure 1 except that the pump body has a base 18' having an upper surface
forming the end wall
13' which is frusto-conical in shape. Consequently, the height of the cavity
11 varies from the
height at the side wall 14 to a smaller height between the end walls 12,13' at
the centre of the
end walls 12,13'. The frusto-conical shape of the end wall 13' intensifies the
pressure at the
centre of the cavity 11 where the height of the cavity 11 is smaller relative
to the pressure at the
side wall 14 of the cavity 11 where the height of the cavity 11 is larger.
Therefore, comparing
cylindrical and frusto-conical cavities 11 having equal central pressure
amplitudes, it is apparent
that the frusto-conical cavity 11 will generally have a smaller pressure
amplitude at positions
away from the centre of the cavity 11: the increasing height of the cavity 11
acts to reduce the
amplitude of the pressure wave. As the viscous and thermal energy losses
experienced during
the oscillations of the fluid in the cavity 11 both increase with the
amplitude of such oscillations,
it is advantageous to the efficiency of the pump 70 to reduce the amplitude of
the pressure
oscillations away from the centre of the cavity 11 by employing a frusto-
conical cavity 11
design. In one illustrative embodiment of the pump 70 where the diameter of
the cavity 11 is
approximately 20 mm, the height of the cavity 11 at the side wall 14 is
approximately 1.0 mm
tapering to a height at the centre of the end wall 13' of approximately 0.3
mm. Either one of the
end walls 12,13 or both of the end walls 12,13 may have a frusto-conical
shape.
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[0030] Referring now to Figure 5, a pump 60 according to another illustrative
embodiment of the invention is shown. The pump 60 is substantially similar to
the pump 10 of
Figure 1 except that it includes a second actuator 62 that replaces the base
18 of the pump body.
The actuator 62 comprises a second disc 64 and a ring-shaped isolator 66
disposed between the
disc 64 and the side wall 14. The pump 60 also comprises a second
piezoelectric disc 68
operatively connected to the disc 64 to form the actuator 62. The actuator 62
is operatively
associated with the end wall 13 which comprises the inside surfaces of the
disc 64 and the
isolator 66. The second actuator 62 also generates an oscillatory motion of
the end wall 13 in a
direction substantially perpendicular to the end wall 13 in a manner similar
to the actuator 40
with respect to the end wall 12 as described above. When the actuators 40, 62
are activated,
control circuitry (not shown) is provided to coordinate the axial displacement
oscillations of the
actuators. It is preferable that the actuators are driven at the same
frequency and approximately
out-of-phase, i.e. such that the centres of the end walls 12, 13 move first
towards each other and
then apart.
[0031] The dimensions of the pumps described herein should preferably satisfy
certain
inequalities with respect to the relationship between the height (h) of the
cavity 11 and the radius
(r) of the cavity which is the distance from the longitudinal axis of the
cavity 11 to the side wall
14. These equations are as follows:
r/h > 1.2; and
h2/r > 4x10-1 meters.
[0032] In one embodiment of the invention, the ratio of the cavity radius to
the cavity
height (r/h) is between about 10 and about 50 when the fluid within the cavity
11 is a gas. In this
example, the volume of the cavity 11 may be less than about 10 ml.
Additionally, the ratio of
h2/r is preferably within a range between about 10-3 and about 10-6 meters
where the working
fluid is a gas as opposed to a liquid.
[0033] In one embodiment of the invention the secondary apertures 15 are
located where
the amplitude of the pressure oscillations within the cavity 11 is close to
zero, i.e., the "nodal"
points of the pressure oscillations. Where the cavity 11 is cylindrical, the
radial dependence of
the pressure oscillation may be approximated by a Bessel function of the first
kind and the radial
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node of the lowest-order pressure oscillation within the cavity occurs at a
distance of
approximately 0.63r 0.2r from the centre of the end wall 12 or the
longitudinal axis of the
cavity 11. Thus, the secondary apertures 15 are preferably located at a radial
distance (a) from
the centre of the end walls 12,13, where (a) "z 0.63r 0.2r, i.e., close to
the nodal points of the
pressure oscillations.
[0034] Additionally, the pumps disclosed herein should preferably satisfy the
following
inequality relating the cavity radius (r) and operating frequency (f) which is
the frequency at
which the actuator 40 vibrates to generate the axial displacement of the end
wall 12. The
inequality equation is as follows:
k0(c) < r < ko(cf)
277f 27-tf
wherein the speed of sound in the working fluid within the cavity 11(c) may
range between a
slow speed (cs) of about 115 m/s and a fast speed (et) equal to about 1,970
m/s as expressed in
the equation above, and ko is a constant (k0 = 3.83). The frequency of the
oscillatory motion of
the actuator 40 is preferably about equal to the lowest resonant frequency of
radial pressure
oscillations in the cavity 11, but may be within 20% therefrom. The lowest
resonant frequency
of radial pressure oscillations in the cavity 11 is preferably greater than
500Hz.
[0035] Referring now to the pump 10 in operation, the piezoelectric disc 20 is
excited to
expand and contract in a radial direction against the end plate 17 which
causes the actuator 40 to
bend, thereby inducing an axial displacement of the driven end wall 12 in a
direction
substantially perpendicular to the driven end wall 12. The actuator 40 is
operatively associated
with the central portion of the end wall 12 as described above so that the
axial displacement
oscillations of the actuator 40 cause axial displacement oscillations along
the surface of the end
wall 12 with maximum amplitudes of oscillations, i.e., anti-node displacement
oscillations, at
about the centre of the end wall 12. Referring back to Figure 1A, the
displacement oscillations
and the resulting pressure oscillations of the pump 10 as generally described
above are shown
more specifically in Figures 1A(1) and 1A(2), respectively. The phase
relationship between the
displacement oscillations and pressure oscillations may vary, and a particular
phase relationship
should not be implied from any figure.
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[0036] Figure 1A(1) shows one possible displacement profile illustrating the
axial
oscillation of the driven end wall 12 of the cavity 11. The solid curved line
and arrows represent
the displacement of the driven end wall 12 at one point in time, and the
dashed curved line
represents the displacement of the driven end wall 12 one half-cycle later.
The displacement as
shown in this figure and the other figures is exaggerated. Because the
actuator 40 is not rigidly
mounted at its perimeter, but rather suspended by the isolator 30, the
actuator 40 is free to
oscillate about its centre of mass in its fundamental mode. In this
fundamental mode, the
amplitude of the displacement oscillations of the actuator 40 is substantially
zero at an annular
displacement node 22 located between the centre of the end wall 12 and the
side wall 14. The
amplitudes of the displacement oscillations at other points on the end wall 12
have amplitudes
greater than zero as represented by the vertical arrows. A central
displacement anti-node 21
exists near the centre of the actuator 40 and peripheral displacement anti-
node 21' exists near the
perimeter of the actuator 40.
[0037] Figure 1A(2) shows one possible pressure oscillation profile
illustrating the
pressure oscillation within the cavity 11 resulting from the axial
displacement oscillations shown
in Figure 1A(1). The solid curved line and arrows represent the pressure at
one point in time,
and the dashed curved line represents the pressure one half-cycle later. In
this mode and higher-
order modes, the amplitude of the pressure oscillations has a central pressure
anti-node 23 near
the centre of the cavity 11 and a peripheral pressure anti-node 24 near the
side wall 14 of the
cavity 11. The amplitude of the pressure oscillations is substantially zero at
the annular pressure
node 25 between the pressure anti-nodes 23 and 24. For a cylindrical cavity
the radial
dependence of the amplitude of the pressure oscillations in the cavity 11 may
be approximated
by a Bessel function of the first kind. The pressure oscillations described
above result from the
radial movement of the fluid in the cavity 11, and so will be referred to as
"radial pressure
oscillations" of the fluid within the cavity 11 as distinguished from the
axial displacement
oscillations of the actuator 40.
[0038] Referring to Figures 3 and 1A(2), the operation of the flap valve 50 as
described
above within the pump 10 causes fluid to flow in the direction indicated by
the dashed arrows in
Figure 2A(1) creating a negative pressure outside the primary aperture 16' of
the pump 10.
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Referring more specifically to Figure 3, the flap valve 50 is disposed within
the primary aperture
16' so that the fluid is drawn into the cavity 11 through the primary aperture
16' and expelled
from the cavity 11 through the secondary apertures 15 as indicated by the
solid arrows, thereby
providing a source of reduced pressure at the primary aperture 16'. The fluid
flow through the
primary aperture 16' as indicated by the solid arrow pointing upwards
corresponds to the fluid
flow through the vent holes 54 and 55 of the flap valve 50 as indicated by the
dashed arrows in
Figure 2A(1) that also point upwards. As indicated above, the operation of the
flap valve 50 is a
function of the change in direction of the differential pressure (AP) of the
fluid across the flap
valve 50. The differential pressure (AP) is assumed to be substantially
uniform across the entire
surface of the retention plate 52 because its position corresponds to the
centre pressure anti-node
23 as shown in Figure 1A(2), which is generally aligned with the primary
aperture 16' in the
base 18 of the pump 10 and, therefore, a good approximation that there is no
spatial variation in
the pressure across the valve 50. When the differential pressure across the
flap valve 50 reverses
to become a positive differential pressure (+AP) as shown in Figure 2A(1), the
biased flap 51 is
motivated away from the sealing plate 53 against the retention plate 52 into
the open position. In
this position, the movement of the flap 51 unblocks the vent holes 55 of the
sealing plate 53 so
that fluid is permitted to flow through the vent holes 55 and then the aligned
vent holes 54 of the
retention plate 52 and vent holes 56 of the flap 51 as indicated by the dashed
arrows. This
provides a source of reduced pressure outside the primary aperture 16' in the
base 18 of the
pump 10 as also indicated by the dashed arrows. When the differential pressure
changes back to
a negative differential pressure (-AP) as indicated in Figure 2A(2), fluid
begins flowing in the
opposite direction through the flap valve 50 as indicated by the dashed
arrows, which forces the
flap 51 back toward the closed position shown in Figure 2A. Thus, as the
differential pressure
(AP) cycles the flap valve 50 between the closed and open positions, the pump
10 provides a
reduced pressure every half cycle when the flap valve 50 is in the open
position.
[0039] With further reference to Figures 1A(1) and 1A(2), it can be seen that
the radial
dependence of the amplitude of the axial displacement oscillations of the
actuator 40 (the "mode-
shape" of the actuator 40) should approximate a Bessel function of the first
kind so as to match
more closely the radial dependence of the amplitude of the desired pressure
oscillations in the
14
CA 02764332 2011-12-02
WO 2010/139916 PCT/GB2009/050613
cavity 11 (the "mode-shape" of the pressure oscillation). By not rigidly
mounting the actuator 40
at its perimeter and allowing it to vibrate more freely about its centre of
mass, the mode-shape of
the displacement oscillations substantially matches the mode-shape of the
pressure oscillations in
the cavity 11, thus achieving mode-shape matching or, more simply, mode-
matching. Although
the mode-matching may not always be perfect in this respect, the axial
displacement oscillations
of the actuator 40 and the corresponding pressure oscillations in the cavity
11 have substantially
the same relative phase across the full surface of the actuator 40 wherein the
radial position of
the annular pressure node 25 of the pressure oscillations in the cavity 11 and
the radial position
of the annular displacement node 22 of the axial displacement oscillations of
actuator 40 are
substantially coincident.
[0040] As the actuator 40 vibrates about its centre of mass, the radial
position of the
annular displacement node 22 will necessarily lie inside the radius of the
actuator 40 when the
actuator 40 vibrates in its fundamental mode as illustrated in Figure 1A(1).
Thus, to ensure that
the annular displacement node 22 is coincident with the annular pressure node
25, the radius of
the actuator (ract) should preferably be greater than the radius of the
annular pressure node 25 to
optimize mode-matching. Assuming again that the pressure oscillation in the
cavity 11
approximates a Bessel function of the first kind, the radius of the annular
pressure node 25 would
be approximately 0.63 of the radius from the centre of the end wall 13 to the
side wall 14, i.e.,
the radius of the cavity 11(r) as shown in Figure 1. Therefore, the radius of
the actuator 40 (ract)
should preferably satisfy the following inequality: 0.63r.act
[0041] Referring now to Figure 6, which is an exploded cross-section of the
edge of the
pump 10 of Figure 1, the isolator 30 is a flexible membrane 31 which enables
the edge of the
actuator 40 to move more freely as described above by bending and stretching
in response to the
vibration of the actuator 40 as shown by the displacement of the peripheral
displacement
oscillations 21' in Figure 6(a). The flexible membrane 31 overcomes the
potential dampening
effects of the side wall 14 on the actuator 40 by providing a low mechanical
impedance support
between the actuator 40 and the cylindrical wall 19 of the pump 10 thereby
reducing the
dampening of the axial oscillations of the peripheral displacement
oscillations 21' of the actuator
40. Essentially, flexible membrane 31 minimizes the energy being transferred
from the actuator
CA 02764332 2011-12-02
WO 2010/139916 PCT/GB2009/050613
40 to the side wall 14, which remains substantially stationary. Consequently,
the annular
displacement node 22 will remain substantially aligned with the annular
pressure node 25 so as
to maintain the mode-matching condition of the pump 10. Thus, the axial
displacement
oscillations of the driven end wall 12 continue to efficiently generate
oscillations of the pressure
within the cavity 11 from the centre pressure anti-node 23 (Figure 1A) to the
peripheral pressure
anti-node 24 at the side wall 14.
[0042] For a flexible membrane 31 formed from a simple sheet as described
above
having a uniform thickness (gm) and a Young's modulus (Em) that spans an
annular gap (g)
between the edge of the actuator 40 and the side wall 14 of the cavity 11, the
force per unit
length required to displace the edge of the flexible membrane 31 (Fstreta) by
an axial
displacement (u) may be approximated by the following equation:
Emu'oõ,
Frtretch
2g 2
where u and 8,õ are much less than g. This may be compared with the
approximate force per unit
length required to bend the edge of a disc embodiment of the actuator 40
(Fbend) by the same
displacement:
Eaug:
Fbend = _______________
2R3
where the actuator 40 has an effective Young's modulus (E,,), thickness ((S),
and radius (R). For
the edge of the actuator 40 to vibrate freely, Fstretch should be much smaller
than Fbend which
suggests that the simple flexible membrane 31 should preferably have a
thickness (gm)
characterized by the following inequality:
Eag28,3
E suR3
[0043] In one embodiment wherein the actuator 40 comprises a steel end plate
17 and
piezoceramic disc 20 having overall dimensions of g=-1 mm, 8õ=1 mm, R=10 mm,
and u=10
this inequality requires that the thickness of a flexible membrane 31 composed
of Kapton is
preferably 8,õ << 1,000 microns, and the thickness of a flexible membrane 31
composed of steel
is preferably 8,, << 100 microns.
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WO 2010/139916 PCT/GB2009/050613
[0044] In one non-limiting example, the diameter of the actuator 40 may be 1-2
mm less
than the diameter of the cavity 11 such that the flexible membrane 31 spans
the peripheral
portion of the end wall 12. The peripheral portion may be an annular gap of
0.5-1.0 mm between
the edge of the actuator 40 and the side wall 14 of the cavity 11. Generally,
the annular width of
the flexible membrane 31 should be relatively small compared to the cavity
radius (r) such that
the actuator diameter is close to the cavity diameter so that the diameter of
the annular
displacement node 22 is approximately equal to the diameter of the annular
pressure node 25,
while being large enough to facilitate and not restrict the vibrations of the
actuator 40. The
flexible membrane 31 may be made from a polymer sheet material of uniform
thickness such as,
for example, PET or Kapton. In one embodiment, the flexible membrane 31 may be
made from
Kapton sheeting having a thickness of less than about 200 microns. The
flexible membrane 31
may also be made from a thin metal sheet of uniform thickness such as, for
example, steel or
brass, or any other suitable flexible material. In another embodiment, the
flexible membrane 31
may be made from steel sheeting having a thickness of less than about 20
microns. The flexible
membrane 31 may be made of any other flexible material suitable to facilitate
vibration of the
actuator 40 as described above. The flexible membrane 31 may be glued, welded,
clamped,
soldered, or otherwise attached to the actuator 40 depending on the material
used, and either the
same process or a different process may be used to attach the flexible
membrane 31 to the side
wall 14.
[0045] While the primary component of motion of the edge of the actuator 40 is
substantially perpendicular to the driven end wall 12 or substantially
parallel to the longitudinal
axis of the cavity 11 (the "axial motion"), the edge of the actuator 40 also
has a smaller
component of "radial motion" occurring in the plane perpendicular to the
longitudinal axis of the
cavity 11. For at least this reason, the flexible membrane 31 should also be
designed to stretch in
a radial direction. Such radial stretching may be achieved by forming the
actuator 40 from a thin
elastic material as described above or by incorporating structural features
into the flexible
membrane 31 to enhance the radial flexibility of the flexible member 31 to
stretch and compress,
i.e., the stretch-ability of the flexible membrane 31, with the radial
movement of the actuator 40
to further facilitate the vibration of the actuator 40.
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[0046] Referring more specifically to Figures 7A and 7B, additional
embodiments of the
flexible membrane 31 having structural features that enhance the stretch-
ability of the flexible
member 31 to facilitate the radial motion of the actuator 40 are shown.
Referring more
specifically to Figure 7A, a first embodiment of a structurally modified
flexible membrane 32 is
shown that includes an annular concertina portion 33 extending between the
actuator 40 and the
side wall 14. The concertina portion 33 comprises annular bends in the
flexible membrane 32
appearing as waves in Figure 7A that expand and contract with the motion of
the actuator 40 like
an accordion. The concertina portion 33 of the flexible membrane 32
effectively reduces the
radial stiffness of the flexible membrane 32 thereby enhancing the stretch-
ability of the flexible
membrane 32 and enabling the actuator 40 to expand and contract more easily in
a radial
direction.
[0047] Referring more specifically to Figure 7B, a second embodiment of a
structurally
modified flexible membrane 34 is shown that includes annular, semi-circular
grooves 35
staggered on each side of the flexible membrane 34 between the actuator 40 and
the side wall 14.
The annular grooves 35 of the flexible membrane 34 may be formed by chemical
etching,
grinding, or any similar processes, or may be formed by laminations. The
annular grooves 35 of
the flexible membrane 34 effectively reduce the radial stiffness of the
flexible membrane 34
thereby enhancing the stretch-ability of the flexible membrane 34 to
facilitate the expansion and
contraction of the actuator 40 in the radial direction. Note that the
structures shown in Figures
7A and 7B and similar structures may also beneficially reduce the force
required to bend the
isolators 32, 34 in the axial direction.
[0048] Although the isolator 30 and flexible membranes 31, 32 and 34 shown in
the
previous figures are ring-shaped components extending between the side wall 14
and the actuator
40, the isolator 30 may also have different shapes and be supported by the
cylindrical wall 19 in
different ways without extending fully to the side wall 14 of the cavity 11.
Referring to Figures
8 and 9, alternative embodiments of the flexible membrane 31 are shown
including flexible
membranes 36 and 37, respectively, that function in a fashion similar to the
other flexible
membranes 31, 32 and 34. Referring more specifically to Figure 8, the flexible
membrane 36 is
formed in the shape of a disc, the inside surface of which forms the end wall
12, rather than the
18
CA 02764332 2015-12-09
end plate 17. The end plate 17 which remains operatively connected to the
upper surface of the
flexible membrane 36 as shown. In the embodiments of Figures 8 and 9, the end
wall 12 still
comprises the central portion operatively connected to the actuator 40, and
the peripheral portion
functioning as the isolator 30 between the side wall 14 and the actuator 40.
As such, the flexible
member 36 operates in a fashion similar to that of the other flexible
membranes 31, 32 and 34.
[0049] Referring more specifically to Figure 9, the cylindrical wall 19 of the
pump body
includes a lip portion 19a extending radially inward from the side wall 14 of
the pump body.
The inside surface of the lip portion 19a facing the cavity 11 forms an outer
portion of the
peripheral portion of the end wall 12 that is disposed adjacent the side wall
14. The flexible
membrane 37 may be ring-shaped or disc-shaped as shown and attached to the
inside surface of
the lip 19a of the cylindrical wall 19 to form the remaining portion of the
end wall 12 as
described above. Regardless of the shape of the flexible membrane 37, the end
:vvall 12 still
comprises the central portion operatively connected to the actuator 40, and a
peripheral portion
functioning as the isolator 30 between the actuator 40 and the lip 19a of the
cylindrical wall 19.
As such, the flexible member 37 operates in a fashion similar to that of the
other flexible
membranes 31, 32 and 34. It should be apparent that the structure, suspension
and shape of the
isolator 30 is not limited to these embodiments, but is susceptible to various
changes and
modifications without departing from the inventions described herein.
[0050] In the previous embodiments of the pump 10 shown in Figures 1-9, the
side wall
14 extends continuously between the end walls 12,13 of the cavity 11, and the
radius of the
actuator 40 (ract) is less than the radius of the cavity 11(r). In such
embodiments, the side wall
14 defines an uninterrupted surface from which the radial acoustic standing
wave formed in the
cavity 11 is reflected during operation. However, it may be desirable for the
radius of the
actuator (ract) to extend all the way to the side wall 14 making it about
equal to the radius of the
cavity (r) to ensure that the annular displacement node 22 of the displacement
oscillations is
more closely aligned with the annular pressure node 25 of the pressure
oscillations so as to
maintain more closely the mode-matching condition described above.
[0051] Referring more specifically to Figure 10, yet another embodiment of the
pump 10
is shown wherein the actuator 40 has the same radius as the diameter of the
cavity 11 and is
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CA 02764332 2015-12-09
supported by a flexible membrane 38 having the same characteristics as the
flexible membrane
31 shown in Figure 5. Because the flexible membrane 38 must enable the edge of
the actuator
40 to move freely as it bends in response to the vibration of the actuator 40,
the cylindrical wall
19 of the pump body comprises an annular step 19b in the upper, inside surface
of the cylindrical
wall 19 extending radially outward from the side wall 14 to an annular edge
19c. The annular
step 19b is cut sufficiently deep into the upper surface of the cylindrical
wall 19 so as not to
interfere with the bending of the flexible membrane 38 to enable the actuator
40 to vibrate freely.
The step 19b should be sufficiently deep to accommodate the bending of the
flexible membrane
38, but not so deep as to significantly diminish the resonant quality of the
cavity 11 referred to
above.
[0052] As can be seen in Figures 10 and 10(A), the driven end wall 12
comprises the
lower surface of the end plate 17 and the flexible membrane 38, and has a
radius (rend) that is
greater than the radius of the cavity 11, i.e., rend > r. Thus, the peripheral
portion of the end wall
12 extends beyond the side wall 14 of the cavity 11. Referring more
specifically to Figures
10(A) and 10(B), the axial oscillation of the actuator 40 and the
corresponding pressure
oscillation in the cavity 11 continue to have substantially the same relative
phase across the full
surface of the actuator 40 with the amplitudes of the displacement
oscillations and the pressure
oscillations being more closely proportional at the side wall 14. As a result,
the radial position of
the annular pressure node 25 of the pressure oscillation in the cavity 11 and
the radial position of
the annular displacement node 22 of the axial oscillation of the actuator 40
may be more
coincident to further enhance mode-matching.
[0053] To ensure that the side wall 14 still defines a substantially
uninterrupted surface
from which the radial acoustic standing wave is reflected within the cavity
11, the depth of the
step 19b is preferably minimized as described above. In one non-limiting
example, the depth of
the step 19b may be sized to maintain so far as possible the resonant
qualities of the pump cavity
11. For example, the depth of the step 19b may be less than or equal to 10% of
the height of the
cavity 11.
[0054] Although preferred embodiments of the invention have been disclosed for
illustrative purposes, those skilled in the art will appreciate that many
additions, modifications,
CA 02764332 2015-12-09
and substitutions are possible and that the scope of the claims should not be
limited by the
embodiments set forth herein, but should be given the broadest interpretation
consistent with the
description as a whole.
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