Acoustic pump utilizing radial pressure oscillations
A fluid pump comprising one or more actuators, two end walls, a side wall; a cavity which, in use, contains fluid, the cavity having a substantially cylindrical shape bounded by the end walls and the side walls, at least two apertures through the cavity walls, at least one of which is a valved aperture, wherein the cavity radius, a, and height, h, satisfy the following inequalities: a/h is greater than 1.2; and h 2 /a is greater than 4×10 −10 m; and wherein, in use, the actuator causes oscillatory motion of one or both end walls in a direction perpendicular to the plane of the end walls; whereby, in use, the axial oscillations of the end walls drive radial oscillations of fluid pressure in the cavity.
1. A fluid pump comprising:
one or more actuators;
two end walls;
a side wall;
a cavity which, in use, contains fluid, the cavity having a substantially cylindrical shape bounded by the end walls and the side wall;
at least two apertures through the cavity walls, at least one of which is a valved aperture;
wherein the cavity radius, a, and height, h, satisfy the following inequalities:
a
h
is greater than 1.2; and
h
2
a
is greater than 4×10 −10 m; and
wherein, in use, the one or more actuators cause oscillatory motion of one or both end walls in a direction substantially perpendicular to the plane of the end walls;
whereby, in use, the axial oscillations of the end walls drive radial oscillations of fluid pressure in the cavity;
wherein the cavity radius, a, also satisfies the following inequality:
k
0
·
c_min
2
π
f
<
a
<
k
0
·
c_max
2
π
f
,
where c_min is 115 m/s, c_max is 1970 m/s, f is the operating frequency and k 0 is a constant (k 0 =3.83); and
wherein, in use, the motion of the driven end wall(s) and the pressure oscillations in the cavity are mode-shape matched and the frequency of the oscillatory motion is within 20% of the lowest resonant frequency of radial pressure oscillations in the cavity.
2. A pump according to claim 1 , wherein the ratio
a
h
is greater than 20.
3. A pump according to either claim 1 or claim 2 , wherein the volume of the cavity is less than 10 ml.
4. A pump according to claim 1 , wherein, in use, the frequency of the oscillatory motion is equal to the lowest resonant frequency of radial pressure oscillations in the cavity.
5. A pump according to claim 1 , wherein, in use, the lowest resonant frequency of radial fluid pressure oscillations in the cavity is greater than 500 Hz.
6. A pump according to claim 1 , wherein one or both of the end walls have a frusto-conical shape such that the end walls are separated by a minimum distance at the centre and by a maximum distance at the edge.
7. A pump according to claim 1 , wherein the actuator is a piezoelectric device.
8. A pump according to claim 1 , wherein the actuator is a magnetostrictive device.
9. A pump according to claim 1 , wherein the actuator includes a solenoid.
10. A pump according to claim 1 , wherein the amplitude of end wall motion approximates the form of a Bessel function.
11. A pump according to claim 1 , wherein any unvalved apertures in the cavity walls are located at a distance of 0.63a plus or minus 0.2a from the centre of the cavity, where a is the cavity radius.
12. A pump according to claim 1 , wherein any valved apertures in the cavity walls are located near the centre of the end walls.
13. A pump according to claim 1 , wherein the ratio
h
2
a
is greater than 10 −7 meters and the working fluid is a gas.
14. A pair of pumps according to claim 1 , wherein the cavity comprises two pump cavities that are separated by a common cavity end wall.
15. A pair of pumps according to claim 14 , wherein the common cavity end wall is formed by an actuator.
16. A pair of pumps according claim 1 , wherein the pumps are connected in series or in parallel.
17. A pump for moving a fluid from an input to an output, comprising:
a body having a substantially cylindrical sidewall and two end walls, each of the end walls closing one end of the sidewall to form a cylinder therein having a radius (a) and a height (h);
an actuator responsive to a source of energy to provide a mechanical displacement oscillating at a frequency (f) and disposed in mechanical communication with one of the end walls for displacing the end wall in a substantially axial direction oscillating at the frequency (f) of the source;
at least two apertures extending through the end walls and functioning as the input and output of said pump with at least one of the apertures being about 0.63(a)±0.2(a) from the center of one of the end walls;
a valve disposed within at least one of the apertures to close and open in response to the oscillating motion;
wherein the radius (a) and height (h) of the cylinder are related to each other and the frequency (f) of the source by the following equations:
a
h
>
1.2
,
and
h
2
a
>
4
×
10
-
10
m
,
and
k
0
c
slow
2
π
f
≤
a
≤
k
0
c
fast
2
π
f
,
where
c slow ≈115 m/s,
c fast ≈1970 m/s,
k o ≈3.83, and
whereby, the oscillating end wall creates radial oscillations of fluid pressure in the cylinder to move the fluid from the input to the output of the pump in response to application of the energy source to said actuator.