WO2014118623A2

WO2014118623A2 - A cooling device and a cooling assembly comprising the cooling device

Info

Publication number: WO2014118623A2
Application number: PCT/IB2014/000117
Authority: WO
Inventors: Brian Donnelly; Nicholas Jeffers; Jason STAFFORD
Original assignee: Alcatel Lucent
Priority date: 2013-02-01
Filing date: 2014-01-13
Publication date: 2014-08-07
Also published as: TW201441575A; WO2014118623A3; US20140216696A1

Abstract

A cooling device comprises a heat sink having fins and a piezofan having a piezoelectric element attached to a planar body. The planar body is capable of oscillating at a movable end in response to applying alternating electric current to the piezoelectric element thereby generating an air flow toward an output of the cooling device. A plurality of fins is located between the movable end of the planar body and the output end of the cooling device Each fin has a planar form with a main surface being substantially aligned with the air flow. A cooling assembly comprising such cooling device is also disclosed.

Description

A coou t DEVICE AND A COQUMCS ASSEMBLY COMPRISING THE

COOLING DEVICE

TECH NIC AL FIELD

Ti e prese t inventio is directed _t in general, to ¾ >olfog ©chnt£tues, BACKGROUND

This section introduces aspects that may be helpful in facilitating a better understanding of the disclosure, coordingiy, the statements of this s ction are te be read In this light and are not to be understood as admissions about what is in the prior art or¾ }at is net in th pr or art.

Piezoelectric device® are known, Typfcaiiy piezoelectric device comprises a body of a solid materiat having the property of accumulating electrical charge when a mechanical stress such as a pressure is applied the eupon, Conversely, such piezaeiectrfc body exhibits a mechanical mo^ ent in response to an electric current a plieaf thereto. Some examples of materials exhibiting piezoelectric property are certain crystals or ceramics. One implementation of a piezoelectric device is a piezofan, A piezofan is typically made of a pteoeieetrie element which is physically attached, e,g. boneted, to an end of planar, typicall thin, body (sometimes referred to as blade or cantilever) the other end of the body being free and movable. Wnen an alternating electric current is applied to the piezoelectric element, ihe latter exhibits an oscillating movement, causing the oppssite end of the planar body to move. If the frequency of the alternating current i equal to the resonant frequency of the planar body, the latter produces an oscillating movement the free end thereof, Th oscillation of the free end of the planar body produces an air flow i a similar manner as a conventional hand fan.

Some embodiments of the ilscios re feature a cooing device comprising a heat sink and a piezofan; the heat sink comp ising a plurality of fins of a thermall conductive material and the piezofan comprising a piezoelectric eleme attached to planar body, the planar body being configured to oscillate at a movable end in response to ap lyi g alternating electric curre t to said piezoelectric element and ge ra ing an air flow from an input end of the d&vice to an output end of the device_* wherein a piuraiiy of fins are located between the movable end of the planar body and he output end of the* cooling device; each fin having a planar form with a main surface being mibstantlally aligned with said air flo .

Aeoording to some specific emfeodimersts, the pSezofan and the pluralit of fins are located between s¾e wails

According to some specific, embodiments, a side wail comprises a protuberant portio having a surface configured for directing said ai flow towar said plurality of fins.

According to some specific embodiments., the piezoelectric element and the planar body mm mounted on a support element attached to the heat sink with a damping materia! posiSoned between the support element and heat sink configured for isolating or re w g a vibration caused by the operation of piezofan.

Aeoording t© some specific embodiments, the support element is a rigid rail.

Some embodiments of the disclosure feature a Stali g assembly comprising a heat sink^; and a piezofan; the heat sink comprising a plurality of fins of a thermally conducive material and the piezofa comprising piezoeSectris element attached to a plana body, the planar body being configured to oscillate at a movable end in response to applying aiternatlpg electric current to said pie oelectrfe element and generating an air flow from a input end of the device t© an output end of th«s device, wherein a plurality of fl are located (betwee the movable end of the planar body and the output end of the cooing device; each fin having a planar form wth a main surface being substantially aligned witfi said air tew.

According to some specific embodiments a first c ling assembly with a first pleKofaii is assembled with a second cooling assembly with a second ptezofan, wherein the first ieH?fan is configured to oscillate out of p ase v ih respect to the second p;©2oiari.

BRIEF DESCRIPTION

For a more complet understandiftg of the present diseiosu¾ reference is mw mad to the following descriptions taken in conjunction With fie acfeonipanying dra ings, in which:

FIG. 1 is a exemplary schematic repfeseni on of a front view of a cooling device according to an embodime t;

FiC 2a and 2h are exemplary schematic representations of a cooling device according to a embodiment rs fron view and perspectiv vm respectively; mi

Fli3. 3 Is an exemplary schem tic ep es^nfattd of a eoc#sgi assarrihly composing a plurality of cooling devices aeoordiftg to seme embodiments. iJETAILfip pESGi¾!PTIO«

A trend in p oducing electronic devices is toward: reducing f heir size white enabling such devices of processing i cfeasircgiy larger volumes of data. Processing iarger volume of data ypfea!iy involves higher levels of heat genersion v¾hich in turn would require stronger and nm eff¾ier¾i cooling mechanisms,

One typical option for dissipating heat loads thin electronic eom o rits is the use of passive heat sinks that combine natural convection and radiation heat transfer modes. As component heat loads increase, the size and therefore weight of these heat s ks would typically need to increase to keep TOSpens f temperaiiifes heSpw their threshold values {Le. highest v lue of the temper yr at wjiioh a particular device o erates norrnall ). l-lewever, iacreasing the size of the heat sinks would dause an Increase in the ©verai si¾e of the device w ich is ty lcaify un esirable for fnoderri devices. Therefore, passive moling sy !eiTiS invoive physical limits as to their suitabilit for use In modern electronic devices^

Active coolin§ systems, e.g. the us of rotairig fans, constitute another known solution which, compared to passive codling systems, is typically capable of fer j t larger ya 5itii>¾s of heat from an electronic ooniponeni. l-towever, such active cooling systems typicall suffer from relatively short

equire higher perfomiano a d funcSona!ily couple with lower product votefw . Therefore, ther is a ne« for active ccjoling wlhott lhe ty ical inherent unreliability of f ns lifetime,

Erabodirnerifs of the olsislGsure feature the use of a ie^ an for providinf active cooling, together wil a beat sink fo providing passive cooling, Some solutions directed to the use el a p!ezofa together with a passive beat sink are known.

Howeve , in certain applications it may fee desired to ensure a smooth and yndisturbed flow of the air 1mm the region where the blad is oscillating toward the output of the device. One example of such applications is where various cooing devices are to be assembled adjacent each other, fo xam l in the form of a stack. Indeed in such oases, it is preferred that the air flow is aligned toward the output end of the device substantially undisturbed and as much as possible f e of perturbation .

Herein, the term align as it is referred to air flo Is to be understood to refer t a condition in which air flows in parallel layers and assists the natural buoyanc ' driven tow within the beat sink when; the device is In o e, with no or negligible How disruption between the lay s of the flow and with absence of vortices in these layers,

Referring now to Fig. 1 , there is provided a cooling device 1 comprising a piexofan generally represented by reference nurnerai 11 and ¾ conveetion heat sink generally represente by reference numeral 12· ^'The piezofsn 11 comprises a bas portion 111 and planar portion 112, herein also: r ferred to as a cantilever or a hfade> The base portion may be a piezoelectric element, i.e. ma e of a iezoelect ic material such as for exam l Gera te, Th planar portion 112 is slash ; at a first end to the base portion 111 and has a second end opposite to the first end which is free and movable. The mounting point for the planar portion i 12 may also be on an external rai! or solar shield. The heat stefs 2 comprises plurality of fins 121 disposed a! convenient locations vali lti the eo¾fing device 1 , The eeeiipg device 1 may further comprise side wall® 122. The side-waits may also have geometry to assist the movement of air within the eoo!ing devic as will lie de¾cdt>ed fwrinef below, The device 1 further comprises an input er¾S 123 f om whic air used for cooling may flow Inside the device 1 arid an output end 124 from which such air exits toe device afte being fanned by the operation of the pie¾ofaH 11>

in operation, when it is desired to coo! 8 heat load of an electronic equipment, the piezofan ma be activated. The eat loads of individual electronic components ma be spread across the body of the heat sink has© materia!! in simitar fashion as done in the ease of known e iprneni As d &crlbed_: further afeove, fe applying an aSiernating current hot shewn) to the bas portion 111, the latter which is niade of iez el ct ic material exhibits an opiati g displaoemenf which is then transferred to tti cantilever 112. If the frequ ncy of the alternating current is the same as the resonant frequency of the cantilever. It may paus the tter to oscillate at suc resonant frequency. Such oscillation is mawnu n in amplitude at the free and movable © id of the cantileve and may cause air flow in the surrounding air forcing the latter to flow tow d the output end 124 of the device 1, The oscillation of the movable end of the cantilever 1 Is shown in F f <3. 1 b doui>ie ¾eaded arrow ^"OS ,

The air flow Is forced to move {pushed} away from the regio wh r the movable end of the cantilever 112 Is osolaipg as a result of toe oscillating action of said movabl end. This effect is shown in FK3. by means of arrows Al , A2 and A3, where arrows^■At illustrate th© direction of the low of the air into the coolin devic at the input end 123 thereof, arrows A2 show the direction of few of the air after entering in the deyio 1 and befor r^aohipg the oscillating end of the cantileve 112 and arrows A3 show the direction of flow of the air between the osciaSng end of the ca ntilever 11 and the output end 24 of tii€ coo!ipg device I .

The cowhided effect of th oseiilaio of the movable end of the cantilever and the flow of fie air out of the cooling device may further generate a vacuum effect in the region of the air flow upstrea the oscillating end of the cantilever {i.e. prior to reaching the osciafrig end) which in torn contrijutes to drawing more outside ir inside the cooling device 1 in the direction of arrows A1 and M,

As if is clearly shown in FSG. 1 the plurality of fins that are located betwee the movabl end of th planar body 1 2 a nd the output end 124 of the cooling device serve for aligning the air flew A3 due t their planar form and in particular to the shape of the main surface 1 2a of each fin which assists a smooth aod undisturbed exit of th air ou of th© device 1 , This regio is identified in FIG. by reference rturrterai R1. In the example of FiG. 1 ₍ the device is show to be in vertical position with the gravity vector i!iu f ated by row G. Therefore, it ma be observe that the direction of flow A3 of the air is ligned wit buoyancy force whie i operation opposes the gravity vector G I FiG 1.

in the context of the present disclosure the main surface of a fin, haying planar fo m_* is to fe understood to refer to the surface with the highest area in the three dimensional body of the fin.

In order to ens re an opfimurn undisturbed air fiow in region R1, it is preferred thai the shapes of fins, o any other intervening structure present in said regi n, be designed such that the generation of vortices in the upstream air flow is avoided and fiow is aligned vvih riving buoyaney f or oes so that heat transfer is enhanced, and quality of airflow nt ring any further devices installed upstream a partiGtilar devic (as shown in the exam le of FIG, 3 is improved ,

In FIG. 1 , the surfaces 1:23 of the fins 121 are shown to fee planar and parallel to eac other. However, this Is only exemplary and other Gor¾figu rations of the surface may also be used as long as they ar© within the scope of the claimed invention such surfaces faef!iate a natural convection o the air flow and increased heat transfer surface are f om the oscillating end of the cantilever 112 to the output end of the cooling device substantiall yyithoyt vortices travelog out of the output end of the device (e.g. Into upstream devices}. For example, such surfaces may have a curved shape or the fin¾ rnay e arranged in a noi isaraiiel mariner. v R*a§ 0u&iy, the conduction of the air flew torn the mput end of the cooling device 1 to the osclaiing end of the cantilever 112 (arrows A1 and A2) is also free of vortices at least in a first portion of such air flow. This egion is identified in FIG. 1 by reference numeral R2,

in this manner, air is actively mad© to flow inside the cooling device 1 , through the fins 21 thereby cooling the f and then made to exit the cooling device 1 torn the output end 124.

FIG, 2a shows a /front ie of an exemplary cooing device according to a further e diment of the disclosure a d FIG. 2b shows a perspective view of the device of FIG, 2a. in FlGs. 2a and 2o_t unless otherwise provided, like efements have been given like reference numeral as those of FIG. 1. The embodimen shown in F!Gs. 2a and 2 b is similar to that of FIG. 1 with the exception thai the cooing device of FIGs, 2a and ,2b further cornprise one or more pfotufeeFahi porfiofss 126, 126 on corresponding side walls 122a and 122 b.

The use of s«ch protuberant portions ay be advantageous as they ' may contribute, d«e to their specific geometry and location, to an improved flow o the air in region R1, as long as such geometry does not hinder the buo ancy driven air flow path, at least between the movable end of the cantilever 1 12 and the output end 124 of the cooling device 1 ,

For example I FIG. 2a, incoming air may be drawn inside the cooling device as shown by arrows &1< However when such ai re ches the vlelniy of the protuberant portions S and 1 6, the specific shape f these protuberant portions may deflect the direction of the flow of the air slightly toward the center of the air flow (close to the middle of th ooolng device where the cantilever 12 is located in H , 2a . iuoh defleclro of the flow of the air is shown in FIG. 2a by arrows A2 which ¾ this case, contrary to the arrows $ of FIG, 1 which are sub tantally straight, present certain angle toward the center of the flow. The overall effect of the deftection may therefore be considere as causing air flow to be more concentrated {cente e } toward the Genjer of the osdllation of the movabl end of the cantilever 112, the cantilever 11 asci!tates, it pushe at least a part of the concentrated air to the sides which in turn i §

reflected from the corresponding sun¾oe¾ 12&a and 128a toward the fins 121 u stream the protuberant portions 125 and 126, thereby ear^ytlng to a s ronger or faster air flow tsvv rd the output end 124 of the cooling device 1. in the e¾¾mpi shosi i in FIGs. 2a and 2b^' the proiui»ranL po tions 125 nd 126 present curved surfaces pr^eeting Inside fee cooling de ic fro the side walls 122a and 22ί> respectively, However this is only exemplar and th rotu <efanl portions 12f> and 1:26 may' have an ¹ other convenient shape as long as such shape contributes to an improved flo of the air in gion E1 anel is hot invasive to buoyancy fiows %t>e the device is in operation. For example, the protuberant portions may have piano loped surfaces on each side instead if curved surfaces as shown in FiGs. 2a and 2b: likewise they may be located closer or farther awa from the output end 1 4 ae^f i g to the specific desiig required,

In some embodiments, the protuberant portions may e made of inserts fiat may h Βά ά to the bas strtloture of the cooling device when needed or eri KSved therefrom when such need no longer exists. In some embodi en s such inserts ma be made of plastic or other suitable materia!. This o tion has fne advantage of providing cost optimization as the heat sink may first extrude by standard methods of mass manufacturing and then according to a specie

The cooling device as proposed herein further provides the capability of being ssembled; as is described further below,

FIG. 3 is exem l ry sehernattG representatio of a cooling assembly iO oomprising a plu ality Of cooling devices according to som embodi e ts. I the example shown in FIG 3 twelve individual coolin devices P1-D11 ar s own assembled in two rows LI , 12 and six eoiumns€i« ¾ However, the disotosiire is not so limited and any convenient numbe of cooling devices ma be assembled to form the cooling assembly as proposed herein.

As shown in FIG, 3. an output end of a cooling device located in the tower row L2 is ooupled to an input end ©fan adjacent cooling device located tn tire upper ow? Li, For example with reference to the eoo!ing device D6 in the upper row L1 an the cooling device D 2 in the lower row L2, it may be observed that these two cooling devices are assemfeied variicaly with respect to eac other and that the output end E-D¾2 of the cooling devic 0 2 is coupled to the input end E- S of file cooling device D6.

Herein fie term cou ling is to be understood to refer to an suitable 5 joining or connect irsg of the Output end of a first cooling device to the Input end of a second cooling, device, Irrespective of whether or not such joining of c¾nPeoting involves a dli¾ef physieal contact between the two evices, as Song as such joining or connecting allows for a fiow of air from the output end of the first cooling device to the input d of the second cooling device.

l o M operation, ineoMrig air may enter the corresponding Input ends of the cooling devices D7~D 12 ideated in th lower ow L2_: as shown by arrows A1. The activatio ©f th piezofans provided inside each cooling device may f enerate an air flow towa d the res ctive output ends of each coding device in similar fashion as was already described itft inf enc to F!Qs, 1, 2a and

15 2b. Tne gravity vector is shown fey arrow As the airflow exits the output ends of eac f the cooing devises D?~D12_T i is then entered in ttw corresponding cooling devices D1~D6 through the respective input ends fier of- For example air flo exiing the output end OE^D1 of oooling devic D1 may enter flie input end ΙΕ~Ε)β of coo!sng device Oi. s mentioned with reference to FlGs. 1

20 2a and 2h, the air low exling the lower cooling device D12 and sni ing th tipper cootlng device D8 has b en aligned with rtatara! con entSe« which is advantageous as i enables an asy and smooth flow of the air from fce lower cooling device to the upper cooling device. Furthermore, the absence of additiona obst icive st uGfures a!ong the path of the air flow at the interface

25 between the output end of the lower cooling device and the input end of the upper cooling device ensures a substantially undisturbed mixed convection ich is dvantageous ir¾ particular w s ere a hig number of cooling devices are assembled

The cooling device m disclose here in may comprise additional 30 elements to isolate or substantiaiiy reduce vibration caused by the operation of the p!ezofan. o example such isolation element may be made of a rigid rail whereupo the piezofsn may be mounted. Such rigid rail ma fee f%e4 to the heat sjhk or the: solar shield anange esit with additional damping material postion d between the rail arid eat sink or solar shield,

Another solution to reduced vibration and struc&tre feorne n¾se hen an assembly of devices is used may fee achieved by operating adjacent oscillating s blades out of hase, for example at 90 degrees with respect to each other, thereby educing o eariGeiitng such unwant p enomen .

r¾rfhemwe, the above two solutions m y foe comfoine¾!.

The proposed se!uta according to the various embodiments disclosed erein enables a qpr bined action of an apt ve cooling mela ism with a0 assive cooling mechanish white th use of conv tional 1wm is avoided thereby in i© M¾ reitabi¾, size, lifetime and power consumption,

Anot e advantage of the eeofihg device as roposed In the v rious embodim ts provided eein is that the use of the activ cooling mechanism, Le, activating the piezofan, may be made In a seieAe maftner. In other words,s the piezofan 11 may be turne off when the cooing device car? satisfactorily operate to cool an eiectrohle component using solely the heat sink 12 by natural oonvec o iijassi e cooling ; ni be turned on only wrien an active ooo!ir¾g is required in combination with the natural convection heat sink. This possibility allows for saving in energy consumption and increases the lifetime of0 th device whioh would otherwise occur earlier as the device wou wear out earlier due to eontiftuotis usag¾.

The introduction of the piezofan i a coolin d ice may not degrad heat transfer due to natural convection, t rattier is busyahcy assisting ¾Aich improves heat transfer considerably by increasing the totai air fiew rate, S thereb optij-nmpg the thermal and cost aspects of overall cooling device.

Those skilled in the art to which this application relates will appreciat that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.

Ills to ¼e_: noted that the list of structures as reeled in the claims is not exhaustive and fiat one skilled in the art understands that equivalent structures can be substituted lor the recited stricter© vw Qat departing from the scope of the iSisciosure.

Furthermore, the various rn o N^nls of the present eisc!oare may be combine as k g as .such correlations is corr aibte ancho cs^piinentar .

Claims

WHAT IS CLAIMED IS:

1. A cooling device comprising a heat sink and ¾ piezofap; file heat sink

and tie p zafm com rising a piezoetecirio element attached ip a planar body, the planar body eing configured to oscillate at a movable end in response to applying aMem&ting electric current to said piexoeiectric element and generating an air flow from ah input end of the device to an output end Of the device, wherein plurality of fins are located between the movable end of the planar body and the output end of the sooting device each fin hawing a planar form with a main surface being substantially signed with said air flow,

2. The cooli g device of claim 1 wHereln the pie^ofen and the plurality of ins a e located bet ee side wails. 5 . The eoolng device of ciaim 2, wherein a side wall comprises protufcerar portion having surface co figur d fo directing sai air fl w toward said plurality of fins,

^•4 The coo! ins dovie© of ciaim 1, wherein the iezoelectric element and the 0 plana r body are mo un ed on a support el m nt attached to the heat sink with a dam ing material positione between the support element and heat sink configured for isolating or reducing a yioration caused by the operation of pie^oiap. 5 5, The cooling device of claim 4, wherein the support element is a rigid rail.

&, A cooling assembl ce-rnprising a heat sink and: a piezofan; the heat sink comprising a plurality of fins of a thermally condyctive material and tie piezofa comprising a pie oelectric element attaohed to a planar body, the planar bodyC being configured to osdliat at a movable erwi in response to applying alternating electric current to said piezoelectric element and generatin§ an air How from an !npai end of the device to m output end of the device; h&mm a piumty of Irw are located bet een the movable end of the planar body ar¾l the output end of the cooing device; eac fin having a planar form wit a mai surface being substaritMlv al sed w$h said air flow.

7-

first pseziofan & assembled with a second cooing assembly with a second pte¾ofei, *erei the first j®Eoian is oonfigoreo: to oscillate out of p ases ilh respect to the seoond piezofan.