WO2015113938A1

WO2015113938A1 - Cooled component enclosure

Info

Publication number: WO2015113938A1
Application number: PCT/EP2015/051506
Authority: WO
Inventors: Gwendolyn Anita Luiten
Original assignee: Koninklijke Philips N.V.
Priority date: 2014-02-03
Filing date: 2015-01-26
Publication date: 2015-08-06

Abstract

An enclosure for one or more electronics components has an air movement device within the outer housing, but its output flow communicates with the outside of the outer housing through a passageway.

Description

Cooled component enclosure

FIELD OF THE INVENTION

This invention relates to enclosures for housing components which generate heat and therefore require cooling. The invention further relates to a module comprising the enclosure and also to a method of cooling electronics components.

BACKGROUND OF THE INVENTION

Sealed electronic enclosures are preferred for use in harsh or outdoor environments. Such enclosures are limited in their ability to provide thermal cooling. The heat transfer characteristics at the outside of the enclosure limit the power dissipation and therefore the possible performance of the electronics inside. To increase the heat transfer at the outside of the enclosure, it is known to employ cooling fins and/or air movement devices at the outside of the enclosure.

Especially for electronics enclosures that are mounted in masts or towers, such as outdoor lighting products or telecommunications modules, the size, weight and lifetime of the electronics modules are key indicators. Personnel working in a mast can often only use one hand for instalment so that weight and size need to be kept down. Furthermore, both mounting volume and weight bearing capabilities of a mast are limited. Increasing the volume and weight availability by installing new masts is extremely expensive and subject to planning regulations.

Maintenance such as fan replacement can be prohibitively expensive dependant on the location of the mast or tower.

Passive cooling options (such as heat sinks) offer limited heat transfer coefficients. In order to increase the cooling of the outside surface of an enclosure, either an increased surface area, or an increased flow of cooling air must be supplied. An increase of the cooling surface adds to the volume and the mass of the enclosure, and an increase in the flow of cooling air using movement devices at the outside of the enclosure can limit the module lifetime, because the air movement device is subjected to the harsh environment that required the sealed enclosure in the first place. There is therefore a need for an enclosure for electronics components which enables a level of cooling to be provided while reducing difficulties with maintenance or repair. The enclosure should enable the volume and weight of the module (i.e. the enclosure and its contained components) to be kept low.

SUMMARY OF THE INVENTION

The invention at least partly fulfils the aforementioned goal.

The invention is defined by the independent claims. The dependent claims provide advantageous embodiments.

The enclosure design of the invention mounts an air movement device within the outer housing. A passageway extends to the outside of the outer housing. In this way cooling can be provided by an air movement device, while the air movement device is protected from the environment in the same way as the other components to be protected. There are known air movement devices which can operate over a distance, for example with the use of a (resonant) tube. Unlike a fan, the air movement device and passageway can provide a seal to the inner end of the passageway so that the passageway does not connect the inner enclosure volume to the exterior environment. The only moving part in contact with the outside environment can be a column of air in the passageway.

This seal can be implemented by the design of the air movement device, which has a single output so that no flow passes through the device. In addition, if a long passageway is provided, a plug of air in the passageway can remain inside the passageway while the device is in use, which also provides a form of seal which reduces or prevents the external air reaching the internal components. The term "seal" should be understood accordingly.

The enclosure can have a plurality of passageways extending from the air movement device to the outside of the outer housing. The enclosure can also have multiple air movement devices.

The, or each passageway preferably comprises a tube. This preferably is designed to provide a resonant column of air, which is excited into resonance by the air movement device. However, design of the tube can also be to provide non-resonant column of air. The, or each tube can have an open end outside the outer housing which is directed parallel to an adjacent surface of the outer housing. In this way, a flow of air along the outer surface of the outer housing is provided giving cooling of extended surface area. The enclosure can further comprise a heat sink located outside the outer housing. The passageway can then have an open end outside the outer housing which is directed to the heat sink. The heat sink improves the cooling function.

The air movement device can comprise a resonant synthetic jet device and the or each passageway comprises a resonant air tube. The air movement device can be a diaphragm device (similar in structure to a loudspeaker), a piezoelectric jetting device or a piston device.

Some devices rely on resonance within the passageway. A mass can be provided within or around the passageway for controlling the resonance frequency of air within the passageway.

According to the invention there is provided a module, comprising an enclosure according to the invention and an electronic system within the enclosure. The module may encompass the electronic system.

The electronic system can be any electronic apparatus which will benefit from cooling (for example to enable an increase in power or to enable increased lifetime) and which may be deployed outdoors or in other harsh environments where protection is desired. By way of example the electronic system can be a lighting system or telecommunications apparatus. The electronic system can be a computer or (central) processor unit ((C)PU) of some kind that needs to operate in harsh environment such as in automotive (car, boat or aircraft) where such devices must operate under the hood, or fuselage, in cowlings of engines of such devices. The module may be a lighting module, luminair, wireless communications module, radar module, board computer for any purpose, etc. having the relevant electronics inside. Electronics can be based on integrated circuits of semiconductor chips and/or of conventional discrete electrical elements.

According to the invention there is also provided a method of cooling one or more electronics components with advantages as described for the enclosure and/or the module.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows a first example of enclosure;

Fig. 2 shows a second example of enclosure;

Fig. 3 shows a third example of enclosure; Fig 4 shows a fourth example of enclosure;

Fig 5 shows a fifth example of enclosure; and

Fig 6 shows a sixth example of enclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to the invention there is provided an enclosure for one or more electronics components in which an air movement device is within the outer housing but its output flow communicates with the outside of the outer housing through a passageway.

In embodiments, the air movement device generates a so-called synthetic jet. Synthetic jets are formed by periodic suction and ejection of fluid out of an orifice bounding a cavity, and for example caused by periodic motion of a diaphragm. This diaphragm can be built into one of the walls of the cavity or suspended within the cavity or driven to reciprocate within the cavity.

During an ejection phase a vortex, accompanied by a jet, is created and flows downstream from the jet exit. The primary jet induces a secondary flow, thus creating an increase in flow rate. Once the vortex flow has propagated downstream, ambient fluid from the vicinity of the orifice is entrained. The bulk of the high speed fluid has moved away from the orifice, avoiding re-entrainment, while quiescent fluid from around the orifice is sucked into the orifice.

A synthetic jet is known as a "zero-mass-flux" jet because it is comprised entirely of the ambient fluid. This property means that the output orifice can be the only opening to the interior of the device.

By coupling the output orifice to a passageway, the synthetic jet device can essentially terminate the passageway in a sealed manner, so that the synthetic jet device can be located inside an enclosure, deliver flow to the outside of the enclosure through the passageway, yet not require any flow communication between the inside and outside of the enclosure. This offers the advantage of being able to protect (vulnerable) components from harsh environments by enclosing them in an enclosure and provide cooling for the components with a cooling device that is itself protected by the enclosure.

Fig. 1 shows an example of enclosure for one or more electronics components

10. The enclosure comprises an outer housing 12 which provides a sealed environment for the components 10. An air movement device 14 is provided within the outer housing 12 and a passageway 16 extends from the air movement device to the outside of the outer housing. The outer housing 12 is sealed around the passageway 16 so that the inner volume remains sealed. The air movement device 14 provides an airtight seal between the inside and outside of the outer housing. This is possible if the air intake to the air movement device and the expelled air are both from the ambient air outside the outer housing 12.

The air movement device is a zero -mass- flux device, and has a single orifice which functions both as the intake and outlet port. This single orifice connects to one end of the passageway inside the outer housing 12, whereas the other end of the passageway is outside the outer housing 12.

The passageway is shown as a tube in Fig. 1, and the open end at the outside of the outer housing 12 is directed parallel to an adjacent surface of the outer housing. In this way, an air flow is created along the surface of the outer housing 12, to carry heat away from the outer surface. The flow can be directed to regions corresponding to the location of heat generating components within the enclosure.

Fig. 1 shows an air movement device 14 with a single output passage.

Fig. 2 shows the air movement device with three output passageways, each providing an external air flow to a respective portion of the outer housing 12. There can instead be multiple air flow devices each with one or more outlet passages.

Figs. 1 and 2 shows schematically how the jet of air at the outlet entrains ambient air (represented by arrows at the tube exits) as explained above.

Fig. 2 also shows one possible use of the enclosure, in which the electronic components 10 comprise a lighting system e.g including a Light Emitting Diode (LED). Reflectors are shown as 22. This arrangement can for example be used for outdoor luminaires such as street lighting. The size of the luminaire is limited which limits the passive cooling properties. Use of finned heat sink surfaces may not be desired for aesthetic reasons. LEDs in particular are lighting systems that can generate a lot of heat and thus may need cooling, especially in situations where intensive light is needed such as e.g. with street lighting or other outdoor luminairs.

For lighting applications, the outer housing can be transparent or translucent. It may be diffusive or scattering, depending on the desired optical effect seen from the outside.

By creating a synthetic air jet, the heat transfer coefficient can typically be increased by a factor of 2 to 3 compared to natural convection. For the luminaire, this means that a considerably smaller cooling surface can be used, giving considerable savings of weight and volume. For applications where a heat sink is not considered aesthetically undesirable, a heat sink can be strategically placed, as shown in Fig. 3. The heat sink 30 is placed on the opposite side of the outer housing to the location of the heat generating components, such as LEDs 20. The passageway at the outlet of the air movement device 14 can then be directed towards the heat sink. A sufficient distance is provided between the heat sink 30 and the exit of tube 16 to enable entrainment of outside air.

The air movement device can take various forms. A synthetic jet can essentially be created using a diaphragm to cause a change in volume of a cavity so that fluid is expelled from the cavity. The volume change is typically more than 1% of the volume. A diaphragm displacement of more than the diameter of the output orifice is used to generate a jet flow. Essentially, a chamber with an output orifice has a controllable volume so that air is expelled and drawn in through the orifice.

It is known that that synthetic jet devices with tubes (functioning as long ports) can function outside the resonance frequency, but they operate much more efficiently if they are in resonance. This is shown in the article "Synthetic Jet Cooling Part II: Experimental Results of an Acoustic Dipole Cooler" by Lasance, C.J.M. et. al, 2008 Twenty-Fourth Annual IEEE Semiconductor Thermal Measurement and Management Symposium : 16 - 20 March 2008, (pp. 26-32).

The arrangement uses a flow device with a relatively long output tube. The function of this configuration is that the synthetic jet device sucks in a volume of air in a first half of the cycle and ejects this as a jet in the second half of the cycle. A body of air is present in the output tube that bounces up and down and functions to physically separate the environment inside the enclosure from the environment outside of the enclosure.

The fast moving jet of air that is ejected in the second half of the cycle entrains the outside air, thus converting a small volume of high velocity air into a much larger volume of slower moving air. It is this entrained air flow that cools the enclosure or the heat sink.

There are restrictions on the size of the tube. The volume inside the tube should be larger than the volume that is sucked in and ejected, to provide the separation between the air at each end of the tube.

The tube acts as an acoustic transmission line. This functionality is for example described in US 2009/0168343.

As explained in this document, the tube length can be designed to exceed λ/10 to avoid Helmholz resonance, where λ is the wavelength of the pressure wave set up in the tube, and which is set by the drive frequency of the device. It can be shown that the transmission line behaviour of the tube will result in a velocity gain if the tube is up to λ/4 in length. In fact, if the tube has a length of (2n+l)* λ/4, then an advantageous gain is obtained, because there will be a standing wave in the tube. It is also known that design modifications can be made to the tube, in order to obtain a more advantageous resonant length of the port, e.g. modifications to the tube wall.

The distance between the end of the tube and a surface area that is to be cooled is also one of the design parameters. In order to obtain good entrainment of air, the end of the tube should be removed some distance from the surface area to be cooled, for example a heat sink on the outside of the sealed enclosure. It has been shown that a distance between 5 and 10 tube diameters works well but in different designs different distances can also work out well. It is known that specific geometries are especially advantageous to maximise entrainment of air (e.g. "air amplifiers", where a fast moving jet emerges from a ring shaped exit and entrains a larger volume of slower moving air through the ring) and these can be applied as well.

Different mechanical actuators can be used as part of the air movement device.

Fig. 4 schematically shows a suspended diaphragm 40 which can be electromagnetically actuated by using a loudspeaker type construction.

Fig. 5 schematically shows the movement 50 of side walls of an enclosure to induce the required volume change. The side walls can be moved by piezoelectric control. Fig. 5 also shows that additional mass 52 can be applied to the passageway (or it can be designed with suitable mass and shape) to influence a resonance frequency.

Fig. 6 schematically shows the movement of a piston 60 to induce the required volume change. The piston can be controlled to oscillate periodically by an external electromagnet system 62.

Thus, it can be seen that there are various different possible implementations of an enclosure with an air movement device.

An example of lighting system has been given above. The enclosure can be used for any luminair or outdoor lighting application such as street lighting, stadium lighting, and automotive lighting (car, boat, aircraft). There are many other applications, such as telecommunications equipment, for example transceiver electronics of a base station or of radar equipment. Of particular interest are tower mounted units, such as radio transmitters and receivers, repeaters, base stations etc. The electronic system can be a computer or CPU of some kind that needs to operate in harsh environment (such as high temp or corrosive fluid or gas phase environment). One example may be in certain automotive applications (car, boat aircraft) where such electronic devices of board computers sometimes must operate under the hood of a car or within cowlings of aircraft engines within high or low temperature regions and/or when travelling through contaminated air (volcano eruptions etc).

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An enclosure for one or more electronics components, comprising:

an outer housing;

an air movement device within the outer housing;

a passageway extending from the air movement device to the outside of the outer housing,

wherein the outer housing is sealed around the passageway, and the air movement device and passageway provide a seal between the inside and outside of the outer housing.

2. An enclosure as claimed in Claim 1, comprising a plurality of passageways extending from the air movement device to the outside of the outer housing.

3. An enclosure as claimed in Claim 1 or 2, wherein the or each passageway comprises a tube.

4. An enclosure as claimed in Claim 3, wherein the or each tube has an open end outside the outer housing which is directed parallel to an adjacent surface of the outer housing.

5. An enclosure as claimed in any preceding claim, further comprising a heat sink located outside the outer housing.

6. An enclosure as claimed in Claim 5, wherein the passageway has an open end outside the outer housing which is directed to the heat sink.

7. An enclosure as claimed in any preceding claim, wherein the air movement device comprises a resonant synthetic jet device and the or each passageway comprises a resonant air tube.

8. An enclosure as claimed in any one of Claims 1 to 6, wherein the air movement device comprises a diaphragm device.

9. An enclosure as claimed in any one of Claims 1 to 6, wherein the air movement device comprises a piezoelectric jetting device.

10. An enclosure as claimed in any one of Claims 1 to 6, wherein the air movement device comprises a piston device.

11. An enclosure as claimed in any preceding claim, comprising a mass within the passageway for controlling a resonance frequency of air within the passageway.

12. A module, comprising:

an enclosure as claimed in any preceding claim; and

an electronic component within the enclosure.

13. A module as claimed in Claim 12, wherein the electronic component comprises a single or more of any one of the following:

a lighting component,

a computer, processor unit (PU),

a part of a telecommunications apparatus, or

a part of a radar apparatus.

14. A method of cooling one or more electronics components, comprising:

providing the electronics components within an enclosure comprising an outer housing;

providing an air movement device within the outer housing and providing a passageway extending from the air movement device to the outside of the outer housing sealed around the passageway,

operating the air movement device to provide movement of air at an open end of the passageway but also to provide a seal between the inside and outside of the outer housing.