U.S. patent application number 12/515999 was filed with the patent office on 2010-01-28 for pulsating cooling system.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V.. Invention is credited to Ronaldus Maria Aarts, Joris Adelbert Maria NIEUWENDIJK, Antonius Johannes Jo Wismans.
Application Number | 20100018675 12/515999 |
Document ID | / |
Family ID | 39179713 |
Filed Date | 2010-01-28 |
United States Patent
Application |
20100018675 |
Kind Code |
A1 |
Aarts; Ronaldus Maria ; et
al. |
January 28, 2010 |
PULSATING COOLING SYSTEM
Abstract
A cooling device comprising at least one transducer (1) having a
membrane adapted to generate pressure waves at a working frequency,
characterized by a first and a second cavity (3, 4), said
transducer being arranged between said first and second cavities,
such that said membrane forms an fluid tight seal between said
cavities, each cavity having at least one opening (7, 8) adapted to
emit a pulsating net output fluid flow, wherein said cavities and
openings are formed such that, at said working frequency, a first
harmonic fluid flow emitted by said opening(s) (7) of a first one
of said cavities is in anti-phase with a second harmonic fluid flow
emitted by said opening(s) (8) of a second one of said cavities, so
that a sum of harmonic fluid flow from said openings is essentially
zero. With this design, sound reproduction at the working frequency
is largely cancelled due to the counter phase of the outlets
resulting in a close to zero far-field volume velocity.
Inventors: |
Aarts; Ronaldus Maria;
(Eindhoven, NL) ; NIEUWENDIJK; Joris Adelbert Maria;
(Eindhoven, NL) ; Wismans; Antonius Johannes Jo;
(Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS
N.V.
EINDHOVEN
NL
|
Family ID: |
39179713 |
Appl. No.: |
12/515999 |
Filed: |
November 27, 2007 |
PCT Filed: |
November 27, 2007 |
PCT NO: |
PCT/IB07/54796 |
371 Date: |
May 22, 2009 |
Current U.S.
Class: |
165/104.19 ;
165/109.1 |
Current CPC
Class: |
H01L 23/467 20130101;
H01L 2924/0002 20130101; H01L 2924/0002 20130101; H01L 23/4735
20130101; H01L 2924/3011 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/104.19 ;
165/109.1 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2006 |
EP |
06125061.9 |
Claims
1. A cooling device comprising at least one transducer (1) having a
membrane adapted to generate pressure waves at a working frequency,
characterized by a first and a second cavity (3, 4), said
transducer being arranged between said first and second cavities,
such that said membrane forms a fluid tight seal between said
cavities, each cavity having at least one opening (7, 8) adapted to
emit a pulsating net output fluid flow, wherein said cavities and
openings are formed such that, at said working frequency, a first
harmonic fluid flow emitted by said opening(s) (7) of a first one
of said cavities is in anti-phase with a second harmonic fluid flow
emitted by said opening(s) (8) of a second one of said cavities, so
that a sum of harmonic fluid flow from said openings is essentially
zero.
2. The device according to claim 1, wherein each cavity has more
than one opening.
3. The device according to claim 1, wherein two transducers (34,
35) are arranged in opposite positions between said cavities (31,
32).
4. The device according to claim 1 wherein a distance d between any
two openings is less than 0.2.lamda., and preferably less than
0.1.lamda., where .lamda. is the wave length in said fluid
corresponding to the working frequency.
5. The device according to claim 1 wherein said working frequency
is chosen such that velocities of said first and second harmonic
flows have a local maximum at this working frequency.
6. The device according to claim 1 wherein said cavities (3, 4)
have essentially equal volume.
7. The device according to claim 1 wherein said openings (7, 8)
have essentially equal cross section area.
8. The device according to claim 1 wherein said openings are
connected to respective cavity via a channel (5, 6).
9. The device according to claim 8, wherein said channels (5, 6)
have essentially equal length.
10. The device according to claim 8, wherein said channels (5, 6)
have essentially equal cross section.
11. The device according to claim 8, wherein a channel connecting
at least one opening of said first cavity extends through said
second cavity, so that said at least one opening is located on the
same side of said device as the openings of said second cavity.
12. The device according to claim 1, realized using micro
electromechanical system (MEMS) technology.
13. The device according to claim 12, wherein the transducer is
formed by etching a silicon substrate.
14-15. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a pulsating cooling system,
i.e. a cooling system where a transducer induces an oscillation
creating a pulsating fluid stream that can be directed towards an
object that is to be cooled. It may be advantageous to drive the
system at, or at least close to, its resonance frequency, in order
to obtain a high fluid velocity.
BACKGROUND OF THE INVENTION
[0002] The need for cooling has increased in various applications
due to higher heat flux densities resulting from newly developed
electronic devices, being, for example, more compact and/or higher
power than traditional devices. Examples of such improved devices
include, for example, higher power semiconductor light-sources,
such as lasers or light-emitting diodes, RF power devices and
higher performance micro-processors, hard disk drives, optical
drives like CDR, DVD and Blue ray drives, and large-area devices
such as flat TVs and luminaries.
[0003] As an alternative to cooling by fans, document WO
2005/008348 discloses a synthetic jet actuator and a tube for
cooling purposes. The tube is connected to a resonating cavity, and
a pulsating jet stream is created at the distal end of the tube,
and can be used to cool an object. The cavity and the tube form a
Helmholtz resonator, i.e. a second order system where the air in
the cavity acts as a spring, while the air in the tube acts as the
mass.
[0004] Another example is given by N. Beratlis et al, Optimization
of synthetic jet cooling for microelectronics applications,
19.sup.th SEMITHERM San Jose, 2003. Here a synthetic jet is
disclosed having two diaphragms each communicating with the same
orifice.
[0005] A pulsating fluid stream (typically air stream) of this kind
has been found to be more efficient for cooling than laminar flow,
as typically used in conventional cooling systems (e.g. cooling
fans). The resonance cooling systems further require less space,
and generates less noise.
[0006] However, in previously proposed systems, e.g. as disclosed
in WO 2005/008348, a certain level of sound reproduction, related
to the frequency of the oscillating air flow, remains.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to reduce the noise
level in a pulsating cooling system even further.
[0008] According to the present invention, this and other objects
are achieved by a cooling device comprising two cavities, the
transducer being arranged between the two cavities, such that the
membrane forms a fluid tight seal between the cavities, each cavity
having at least one opening adapted to emit a pulsating net output
fluid flow, wherein the cavities and openings are formed such that,
at the working frequency, a first harmonic fluid flow emitted by
the opening(s) of a first one of the cavities is in anti-phase with
a second harmonic fluid flow emitted by the opening(s) of a second
one of the cavities, so that a sum of harmonic fluid flow from the
openings is essentially zero.
[0009] The transducer arranged between two cavities will act as a
dipole, i.e. two acoustical sources in anti-phase. The invention is
based on the idea that the harmonic parts of the sound from these
two sources will cancel out. The non-harmonic parts, which
represent the dominating part of the cooling effect, will not add
coherently, and will thus not cancel out.
[0010] With this design, an improved cooling effect is achieved by
means of an oscillating air stream, while at the same time sound
reproduction at the working frequency is largely cancelled due to
the counter phase of the outlets resulting in a close to zero
far-field volume velocity. Consequently, the cooling system
according to the present invention has significantly lower sound
reproduction than prior art "synthetic jet" cooling devices.
[0011] The cooling device according to the present invention may be
used for cooling a large variety of objects through directed
outflow of various liquid or gaseous fluids, not only air. It is,
however, particularly useful for air-cooling of such objects as
electronic circuitry.
[0012] Each cavity may have only one opening, or have more than one
opening. It is important however that the sum of harmonic
contributions from all openings is essentially zero.
[0013] More than one transducer may be arranged between the
cavities. For example, two, oppositely positioned transducers
operating in counter phase will result in a larger air flow. By
"oppositely positioned" is intended a situation where pressure
waves from one transducer are directed into one cavity, while
pressure waves of the other transducer are directed into the other
cavity.
[0014] A "transducer" is here a device capable of converting an
input signal to a corresponding pressure wave output. The input
signal may be electric, magnetic or mechanical. Examples of
suitable transducers include various types of membranes, pistons,
piezoelectric structures and so on. In particular, a suitably
dimensioned electrodynamic loudspeaker may be used as a
transducer.
[0015] The distance between the openings should be short compared
to the wavelength at the working frequency. For two sources (e.g.
two openings) of strength A at a distance d from each other, the
pressure p at distance r from these sources will be
p = Akd sin ( .theta. ) r , ##EQU00001##
where k is the wave number (.omega./c) and .theta. is the angle of
observation. In order to keep this pressure small, according to a
preferred embodiment, the distance d is less than 0.2.lamda., and
even more preferably less than 0.1.lamda..
[0016] There are no absolute requirements on the working frequency.
However, the working frequency is preferably chosen such that the
air velocities and air displacement through the openings have a
local maximum, and typically this occurs in a neighborhood of a
resonance frequency of the device, i.e. a frequency corresponding
to a local maximum of the electric input impedance of the device
(the transducer in combination with the cavities and openings).
Typically the lowest such frequency is chosen.
[0017] Alternatively, the working frequency can be chosen such that
the cone excursion of said transducer has a local minimum at this
working frequency. Typically, this occurs at an anti-resonance
frequency of the device, i.e. a frequency corresponding to a local
minimum of the electric input impedance of the device.
[0018] One way of ensuring that the air velocities are of
essentially equal size and in counter-phase is to provide equal
circumstances for all air streams. For example, the cavities can be
formed to have equal volume, and the openings can be formed to have
equal cross section area. However, this is not a requirement, and
canceling air streams may be achieved also with different sized
cavities and/or openings.
[0019] According to one embodiment, the openings are connected to
respective cavity via a channel (or pipe). This allows for more
design freedom, as the channels can be formed to direct several air
streams towards the same location, and with desired direction. For
the same reason as above, the channels can be formed to have equal
length and cross section area.
[0020] According to one embodiment, such channels are sufficiently
long to act more as tube resonators. According to an alternative
embodiment, the length of the channels is instead sufficiently
short to allow the cavities to act as conventional Helmholtz
resonators.
[0021] A channel connecting at least one opening of the first
cavity can extend through the second cavity, so that this opening
is located on the same side of said device as the openings of the
second cavity. In a case where the cavities have essentially planar
extension and are arranged on top of each other (i.e. like two
discs on top of each other), such a design will enable locating all
the openings on the top or bottom side of the device.
[0022] Two or more devices according to the present invention may
be combined, to form a cooling arrangement with a multiple of two
openings. The average distance between the openings of a first
device and the openings of a second device is then subject to the
same requirements as the distance between the two openings of each
device, and should thus preferably be less than 0.2.lamda., and
even more preferably less than 0.1.lamda..
[0023] According to this design, four (or more) outlets are
arranged close to each other, in relation to the wavelength at the
working frequency. This results in a further reduction of noise
during operation of the cooling arrangement. This is partly due to
a more perfect symmetry of geometry, because of the presence of two
(mirrored but identical) transducers, and partly due to a better
compensation of nonlinear distortion generated by the two identical
loudspeakers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] This and other aspects of the present invention will now be
described in more detail, with reference to the appended drawings
showing a currently preferred embodiment of the invention.
[0025] FIG. 1 shows a cooling system according to a first
embodiment of the present invention.
[0026] FIG. 2 shows an example of the frequency responses of
respectively the electric input impedance, the air velocities, the
air displacement, and the cone displacement.
[0027] FIG. 3 shows a cooling system according to a second
embodiment of the present invention.
[0028] FIG. 4 shows a cooling system according to a third
embodiment of the present invention.
[0029] FIG. 5 shows a cooling system according to a variant of the
third embodiment of the present invention.
[0030] FIG. 6 shows a cooling system according to another variant
of the third embodiment of the present invention.
[0031] FIG. 7 shows a cooling system according to a fourth
embodiment of the present invention.
[0032] FIG. 8 shows a cooling system according to a fifth
embodiment of the present invention.
DETAILED DESCRIPTION
[0033] The cooling system in FIG. 1 comprises a transducer 1
arranged in an enclosure 2. The transducer 1 is arranged to divide
the enclosure into two cavities 3, 4 having volumes V1 and V2
respectively. Each cavity is connected to the ambient atmosphere
respectively via two passages, here pipes 5, 6 having lengths Lp1
and Lp2, and cross section areas Sp1 and Sp2. The pipes 5, 6 have
outlets 7 and 8 positioned on a distance d from each other. The
openings are illustrated as having round shape, but the invention
is not limited to this shape. On the contrary, the openings may
have any shape, and may also be tapered to influence the airflow in
a desired manner.
[0034] The volumes V1 and V2 and the form of the pipes 5, 6 are
chosen such that in use, the transducer will act as a pressure wave
dipole, cause a pulsating flows of fluid present in the cavities
through the outlets which are essential equal and in counter phase.
When driving the transducer at a working frequency, the two fluid
flows will thus counteract each other, thereby suppressing any
pressure waves escaping from the dipole (i.e. disturbing
sound).
[0035] It is noted that the principle is not limited any particular
fluid, but the present description will be based on a device
operated in air, i.e. a device that generates oscillating air
streams.
[0036] According to the illustrated example, this is ensured by
letting respectively V.sub.1 and V.sub.2, L.sub.p1 and L.sub.p2,
and S.sub.p1 and S.sub.p2 have the same value.
[0037] By keeping the distance d short compared to the wavelength,
e.g. less than 0.1.lamda., where .lamda. is the wavelength in air
corresponding to the working frequency, the air pressure radiating
from the dipole is kept very small.
[0038] The volumes V.sub.1 and V.sub.2 and the form of the pipes 5,
6 (from FIG. 1) can be chosen such that there is a specific
frequency for which the air velocities v.sub.1 and v.sub.2 through
each outlet 7, 8 have coinciding local maximums and are in counter
phase. The working frequency can then be chosen to coincide with
this frequency, to ensure a maximum air velocity and thereby
cooling effect. Often, these local maxima coincide with the most
left electric input impedance peak on the frequency scale. This
corresponds to a resonance frequency of the device.
[0039] According to an exemplifying embodiment, a device may have
the following properties:
TABLE-US-00001 Moving mass = 0.57 g Resonance frequency = 370 Hz
Bl-factor = 2.57 N/A Effective diameter = 24 mm DC Resistance =
6.63 .OMEGA. Volumes: V.sub.1 = 3.77 cm.sup.3 V.sub.2 = 3.65
cm.sup.3 Port sizes: L.sub.p1 = L.sub.p2 = 8 cm S.sub.p1 = S.sub.p2
= .pi. (0.0025).sup.2 m2 Electric Input: 2.83 V (1 Watt
nominally)
[0040] For this device, FIG. 2a) to 2d) show the frequency
responses of respectively the electric input impedance, the air
velocities v.sub.1 and v.sub.2, the displacement of the air
particles in the outlets 7 and 8, and the transducer cone
displacement. It is clear that in this illustrated case, the maxima
of the v.sub.1 and v.sub.2 curves coincide with the first resonance
frequency of the system (first local maximum of the input
impedance). Note that, for reasons of clarity, the volumes V.sub.1
and V.sub.2 have been chosen slightly different, so that the curves
in FIG. 2 do not coincide completely.
[0041] Another embodiment is illustrated in FIG. 3, where the tubes
5 and 6 are curved to minimize the footprint, and to minimize the
distance d. The unit consists of two spiral like elements 11,
sandwiching between them a middle plate 12, and closed on their
upper and lower sides by end plates 13. The membrane 14 of the
transducer 1 is arranged in the center of the middle plate 12. The
innermost space 15 of each spiral corresponds to the volumes
V.sub.1 and V.sub.2 in FIG. 1.
[0042] Yet another embodiment is depicted in FIG. 4, where two
cavities 21, 22 are arranged on top of each other, separated by a
middle plate with a membrane 23. In the illustrated example, no
pipes connect the cavities with the ambient air, only two holes, or
very short tubes 24, 25 in the end plates 26, 27. In use, acoustic
waves will radiate from the holes 24, 25 in anti phase, resulting
in combination in very modest sound level.
[0043] The holes 24, 25 need not be arranged on opposite sides of
the cavities. As shown in FIG. 5, they may also be located on the
sides of each cavity. In the illustrated example, the holes 24a-d
and 25a-d, are located pair-wise on respective cavities. The
distribution of holes depends on the desired orientation of the
resulting cooling jet, in FIG. 5 illustrated by arrow A.
[0044] In another variant of the device in FIG. 4, the air from
both cavities 21, 22 may be directed through holes in one of the
end plates 26. As shown in FIG. 6, this can be accomplished by
providing channels 27 leading from the upper cavity 21 through the
lower cavity 22 to holes 28 in the bottom end plate 26. Other holes
29 in the bottom plate 26 lead to the lower cavity 22. In order to
provide similar passages from each cavity, the holes 29 are also
connected to the lower cavity 22 via channels 30, similar in length
and cross section to channels 27.
[0045] As a general comment, it is noted that the number of
channels from each cavity must not be equal. For example, in the
embodiments in FIGS. 5 and 6, there may be more holes from one of
the cavities than the other. It is important, however, that the
total air flow from one cavity is equal in size and in counter
phase compared to the air flow from the other cavity.
[0046] FIG. 7 shows a further embodiment of the invention. In this
case, two cavities 31, 32 are separated by a wall 33 supporting two
oppositely arranged transducers 34, 35, operated in anti-phase. An
advantage with this design is that any differences in geometry
caused by the transducer are compensated for (see e.g. in FIG. 1,
where the transducer consumes more volume in the cavity 4).
Returning to FIG. 7, this embodiment also features one pipe 36
divided in two channels 37, 38 leading to the respective
cavities.
[0047] According to yet another embodiment, illustrated in FIG. 8,
two devices according to one of the previously described
embodiments are used in combination, here devices 41, 42 according
to the embodiment in FIG. 3. The two devices form a cooling system
with two transducers 1 and four openings 7a, 7b, 8a, 8b. All four
openings should preferably be arranged in close proximity, most
preferably within a distance D less than 0.2.lamda., as described
above. Further, as long as the distance is sufficiently small, the
direction of the air streams from the various openings is not
important. It should thus be realized that the openings need not be
parallel and in the same plane, as in the example in FIG. 8, but on
the contrary may be arranged in many other configurations. It
should also be noted that the two devices 41 and 42 need not be
identical, as in the present example. On the contrary, any two
dipole devices may be advantageously combined.
[0048] The person skilled in the art realizes that the present
invention by no means is limited to the preferred embodiments
described above. On the contrary, many modifications and variations
are possible within the scope of the appended claims. For example,
the number of transducers may be increased further, and the
placement and form of openings and channels may be varied depending
on the application.
[0049] Further, the transducer may be implemented in micro
electromechanical system (MEMS) technology, i.e. realized on a very
small scale. More specifically, on such a small scale, an entire
cooling device, including transducer, cavities, openings and any
channels, can be completely embodied in silicon using e.g. etching
technology. Such a device can advantageously be integrated with an
IC to be cooled, e.g. a micro processor. By providing cooling by
means of a cooling device on the same scale as the object to be
cooled, the cooling may be made more efficient. Of course, a
silicon device can be combined with additional channels connected
to the silicon substrate.
* * * * *