electroncs cooling

8/11/2019 electroncs cooling

1/42

The topic itself is made up of 2 Words-ELECTRONICS + COOLING

Electronic equipment has made its way in to practically every

aspect of modern lifeElectronic components depend on the passage of electric currentso there is heat generation due to i^2R losses. Which needs tobe cooled.


2/42

Eects of !amaging "eat

E#tremetemperaturescauses$

%. &udden and totalfailure from which

recovery is notpossible

2. '() based devicesmay e#perienceintermittent

*uctuations inoutput

+. Reducedoperational life


3/42

Eects of !amaging "eat

,et us tae an e#ample

,aptop fans govern the cooling of the internal components.&hould the fan begin to fail then the hard drive/ as ane#ample/ may sustain damage. This can result in slow

performance/ data loss and eventually a hard drive crash. "eat-related damage is among the worst because it causes

additional stress to 0ust about everything that maes yourcomputer function. 1nce the interior of a computer beginsto heat up to 3)4 serious hardware damage will occur.

This damage will be irreversible if the heat problem is notaddressed quicly.

"ence electronic cooling is very essential


4/42

Thermal resistance is the temperature dierence/at steady state/ between two de5ned surfaces ofa material or construction that induces a unitheat *ow rate through a unit area/ 67m2(W

T"ER89, RE&'&T9:)E


5/42

Thermal interface materials;T'8s is generated between thetwo metals and the E8> generated depends on the temperature dierence.

To illustrate the &eebec Eect let us loo at a simple thermocouple circuit asshown in >igure

The thermocouple conductors are two dissimilar metals denoted as 8aterial # and

8aterial y. 'n a typical temperature measurement application/ thermocouple 9 is used as a

?reference? and is maintained at a relatively cool temperature of Tc. Thermocouple= is used to measure the temperature of interest ;Th< which/ in this e#ample/ ishigher than temperature Tc. With heat applied to thermocouple =/ a voltage willappear across terminals Tl and T2. This voltage ;@o


7/42

Aeltier eect

'f we modify our thermocouple circuit to obtain the con5guration shownin >igure it will be possible to observe an opposite phenomenon nownas the Aeltier Eect.

'f a voltage ;@in< is applied to terminals Tl and T2 an electrical current;'< will *ow in the circuit. 9s a result of the current *ow/ a slight coolingeect ;Bc< will occur at thermocouple 0unction 9 where heat is absorbedand a heating eect ;Bh< will occur at 0unction = where heat is e#pelled.:ote that this eect may be reversed whereby a change in the directionof electric current *ow will reverse the direction of heat *ow.


8/42

"eat transferringtechniques

conduction

convection

radiation

:atural >orced

Watercooling

9ir cooling


9/42

9ir cooling

Air coolingis a method of dissipating heat.

't wors by maing the ob0ect to be cooled have a larger surface areaor have an increased *ow of air over its surface/ or both. 9n e#ample ofthe former is to add 5ns to the surface of the ob0ect/ either by maingthem integral or by attaching them tightly to the ob0ectCs surface ;to

ensure eDcient heat transfer


10/42

)onduction cooling

This is de5ned as the transfer of heat from one hot part to another coolerpart by direct contact.

The heat is generated in components whenever the electronic system is inoperation. 9s the heat is generated/ the temperature of the componentincreases and heat attempts to *ow through any path it can 5nd.

'f the heat source is constant/ the temperature within the componentcontinues to rise until the rate of the heat being generated is equal to therate of the heat *owing away from the component.

When the electronic system is operating/ the electronic components are itshottest parts.

To control the hot spot component temperatures/ the heat *ow path mustbe controlled. 'f this is not done properly/ the component temperatures are

forced to rise in an attempt to balance the heat *ow. Eventually/ thetemperatures may become so high that the component is destroyed if aprotective circuit or a thermal cuto switch is not used.

)onduction heat transfer in an electronic system is generally a slowprocess. "eat *ow will not occur until a temperature dierence has beenestablished. This means that each member along the heat *ow path must

e#perience a temperature rise before the heat will *ow to the ne#t pointalong the path. This process continues until the 5nal heat sin is reached/


11/42

:atural convection This involves the transfer of heat from a power device by the action of the

natural air *ow ;air is actually a low-density *uid< surrounding and contactingthe device. 8any power devices are rated for natural convection cooling aslong as the air surrounding the unit remains within a limited temperaturerange that is cooler than the device. The advantage of convection coolingis that no fans are required.

)onvection cooling wors best when the products have a natural circulating

source of air. >or enclosed applications/ to insure a natural e#change of air/ anumber of vents should be provided at various locations in the case.

:atural convection is based on the *uid motion caused by the densitydierences in a *uid due to temperature dierence. 9 *uid e#pands whenheated and becomes less dense. 'n a gravitational 5eld/ this lighter *uidrises and initiates a motion in *uid called natural convection currents

)ontd


12/42

Electronic components or A)=s placed in enclosures suchas a T@ or !@! player are cooled by natural convectionby providing a suDcient number of vents on the case to

enable the cool air to enter and the heated air to leavethe case freely. >rom the heat transfer point of view/ thevents should be as large as possible to minimiFe the *owresistance and should be located at the bottom of thecase for air entering and at the top for air leaving. =ut

equipment and human safety requirements dictate thatthe vents should be quite narrow to discourageunintended entry into the bo#.


13/42

orced convection

The convection heat transfer between a solid surface and a*uid is proportional to the velocity of the *uid.

The higher the velocity/ the larger the *ow rate and the higherthe heat transfer rate.

The *uid velocities associated with natural convection currents

are naturally low/ and thus natural convection cooling islimited to low-power electronic systems.

When natural convection cooling is not adequate/ we simplyadd a fan and blow air through the enclosure that houses theelectronic components.

'n other words/ we resort to forced convection in order toenhance the velocity and thus the *ow rate of the *uid as wellas the heat transfer.

=y doing so/ we can increase the heat transfer coeDcient by afactor of up to about %3/ depending on the siFe of the fan. Thismeans we can remove heat at much higher rates .


14/42

Radiant cooling

This is the transfer of heat by means of electromagnetic radiation; energy waves< that *ows from a hot ob0ect ;e.g./ power device< toa cooler ob0ect.

True radiant heat transfer can tae place in a vacuum and does notrequire air. >or e#ample/ our &un not only emits light waves/ but/also infrared heat waves through great distances in space/ whichresults in our Earth having daylight and various degrees of warmth.

Thermal radiation is a direct result of the random movements ofatoms and molecules in matter.

&ince these atoms and molecules are composed of chargedparticles ;protons and electrons


15/42


16/42

9dvantages of air cooling 'ts light in weight

1perated in e#treme climates

8aintenance is easy

!isadvantages of air cooling :oise production is high


17/42

,iquid cooling

'n the future/ new processors might generate too much heat tobe dissipated through direct air cooling and it would follow thatsuch direct cooling for computers and their components willbecome obsolete.

Water cooling is somewhat popular in very high-power

situations.'t is a method of heat removal from components andindustrial equipment.

9s opposed to air cooling/ water is used as the heat conductor.Water cooling is commonly used for cooling steam electricpower plants/ hydroelectric generators/ petroleum

re5neries and chemical plants. 1ther uses include cooling the barrels of machine guns/ cooling

of lubricant oil in pumpsI for cooling purposes in heate#changers/ and recently/ cooling of various ma0or componentsinside high-end personal computers.


18/42

'n most computers/ fans do apretty good 0ob of eepingelectronic components cool. =utfor people who want to use high-end hardware or coa# their A)sinto running faster/ a fan might

not have enough power for the0ob.

'f a computer generates too muchheat/ liquid cooling/ also nownas !ater cooling/ can be a bettersolution.

't might seem a littlecounterintuitive to put liquids neardelicate electronic equipment/ butcooling with water is far moreeDcient than cooling with air.

9 liquid-cooling system for a A)wors a lot lie the cooling

system of a car. =oth taeadvanta e of a basic rinci le

,iquid cooling


19/42

,iquid cooling


20/42

Advantages

Water is ine#pensive and non-to#ic. >or cooling )AJ cores its primary advantage is that its tremendously increased

ability to transport heat away from source to a secondary cooling surface allows forlarge/ more optimally designed radiators rather than small/ ineDcient 5ns mounted

directly on the heat source.

Disadvantages

Water accelerates corrosion of metal parts and is a favorable medium forbiological growth.

!issolved minerals in natural water supplies are concentrated by evaporation toleave deposits called scale.

)ooling water often requires addition of chemicals to minimiFe corrosion andinsulating deposits of scale.

,iquid cooling


21/42

Electronics cooling methods in

industries

$eat sin%s 9 heat sin transfers thermal energy from a higher temperature

device to a lower temperature *uid medium. The *uid medium isfrequently air/ but can also be water

"eat sins are needed when the heat transfer to the ambient air directly

from the top pacage or via the system board is not suDcient to eep thesemiconductor device within the allowable temperature range.

'n electronic systems/ a heat sin%is a heat e#changer that cools a deviceby dissipating heat into the surrounding medium. 'n computers/ heat sinsare used to cool central processing units . "eat sins are used with high-power semiconductor devices such as power transistors / where the heatdissipation ability of the basic device is insuDcient to moderate its

temperature.


22/42

$eat sin%s

9 fan inside the electronic device moves air across the heat sin and out the device.8ost devices also have an additional fan installed directly above the heat sin tohelp properly cool the processor. "eat sins with these additional fans are calledactive heat sins/ while those with the single fan are called passive heat sins.

"eat sins are usually made of metal/ which serves as the thermal conductor thatcarries heat away from the electronic device. "owever/ there are pros and cons to

using every type of metal. >irst/ each metal has a dierent level of thermalconductivity. The higher the thermal conductivity of the metal/ the more eDcient it isat transferring heat.

1ne of the most common metals used in heat sins is aluminum that metal canconduct. 9luminum is also cheap to produce and is lightweight. When a heat sin isattached/ its weight puts a certain level of stress on the motherboard/ which the

motherboard is designed to accommodate. Ket the lightweight mae up of aluminumis bene5cial because it adds little weight and stress to the motherboard.

1ne of the best and most common materials used to mae heat sins is copper.)opper has a very high thermal conductivity. 't is/ however/ heavier than aluminumand more e#pensive. =ut for operating systems that require an e#tensive amount of

heat dissipation/ copper is frequently used.


23/42

9ll electronic components/ from microprocessors to high end powerconverters/ generate heat and re0ection of this heat is necessary fortheir optimum and reliable operation.

9s electronic design allows higher through put in smaller pacages/

dissipating the heat load becomes a critical design factor.

8any of todayLs electronic devices require cooling beyond thecapability of standard metallic heat sins. The heat pipe is meetingthis need and is rapidly becoming a main stream thermal

management tool.

"eat pipes have been commercially available since the mid %MN3Os.1nly in the past few years/ however/ has the electronics industryembraced heat pipes as reliable/ cost-eective solutions for high endcooling applications.

$eat &i&es


24/42

"eat pipes


25/42


26/42

"eat pipe


27/42


28/42

Eective "eat Aipe Thermal

Resistance

9 main heat pipe design consideration is the eective heat pipethermal resistance or overall heat pipe T at a given design power.

9s the heat pipe is a two-phase heat transfer device/ a constanteective thermal resistance value cannot be assigned.

The eective thermal resistance is not constant but a function of alarge number of variables/ such as heat pipe geometry/evaporator length/ condenser length/ wic structure/ and woring*uid.

The total thermal resistance of a heat pipe is the sum of theresistances due to conduction through the wall/ conductionthrough the wic/ evaporation or boiling/ a#ial vapor *ow/

condensation/ and conduction losses bac through the condensersection wic and wall.


29/42


30/42

8odeling stimulation studies

8any stimulationsoftwares present toanalyse the eects

dierent coolingdevices1ne such software is*ow stimulation by&olidworsives a insight onwhat/ how/ when.Easier option toe#periment and select

proper components.


31/42

9AA,')9T'1:&

Aersonal computers

&oldering

=atteries 9lso useful in variety of industries.>rom small scale to large scale. >romdistribustion to manufacturing.Everywhere.


32/42

Aersonal )omputersThe bacside of a

laptop showingfans.

9 heat sin with fan.

"eat sins mounted on A)=


33/42

&oldering

9 schematic representation ofsoldering heat sin

"eat sin for soldering


34/42

=atteries

"eat sin on a motor in carbattery

"eat sin on a

:itro as Engine for R) car.


35/42

1ther applications

"eat sin for ,E!

"eat Aipe assemblies have beenused to solve thermal problems inmotor drives/ &8A&/ transportationapplications/

destop(noteboo(computer serversand telecommunication


36/42


37/42

!ual pieFoelectric cooling 0ets


38/42

&ynthetic Set cooling

&ynthetic 0ets are produced by theoscillation of a diaphragm bounding a

cavity and are comprised of the ambient*uid surrounding the 0et module. This

method of producing an unsteady/turbulent air 0et enables compact and

unique form factors for cooling electronics.9lso/ since synthetic 0ets are inherentlypulsating and turbulent/ they producehigher heat transfer coeDcients thantypical fan *ows and can remove heat

from a surface with lesser air*ow. &everalcase studies were presented to show the

eDcacy of synthetic 0et cooling. &omeunique cooling methodologies that are not

possible with traditional fans were also

described.


39/42

:ano lighting


40/42

Ahase )hange 8aterials and "eat 9ccumulators

Ahase change materials are successfully used as heat-storing materials for airconditioning/ cool bo#es/ eDcient 5re-retarding powders/ as functional materials forself-heating insoles for boots and many other industrial applications. Their use forelectronics thermal management is limited to applications where time-dependentphenomena play a role. >or e#ample/ reference NPU discusses the use of phasechange materials as compared to copper for use in a power semiconductor unit.

)hemical heat accumulators should also be mentioned. >or e#ample/ the use of

composite materials based on granulated open-porous matri# 5lled with ahygroscopic substance can be seen as a new approach to accumulate heat NNU.

The advantage is a signi5cant increase in the heat that can be stored as comparedto sensible heat and latent heat. >or e#ample/ for a %33Q) temperature rise copperabsorbs V3 S(g. Evaporation of water is associated with an absorption of 22N3S(g. The enthalpy of a reversible chemical reaction can reach a value of 333S(g. 9 principal advantage of reversible chemical reactions for heat accumulation

is their ability to store the accumulated energy for a long time/ if the reaction iscontrolled by the presence of either a catalyst or a reagent. "ence/ the ma0orapplications are in the 5eld of summer-winter heat storage for buildings/ etc.)hemical heat accumulators could potentially be used for outdoor electronicapplications when a night-day rhythm is present.


41/42

Thermionic and Thermotunneling )ooling

Thermionic cooling is based on the principle that a high-wor-functioncathode preferentially emits hot electrons VNU. 8aterials available have awor function of 3. e@ or higher/ which limits the use to the highertemperature ranges ;P33 6


42/42

Electrohydrodynamic and Electrowetting )ooling

Date post:	02-Jun-2018
Category:	Documents
Upload:	vishwarocks1011178
View:	219 times
Download:	0 times

electroncs cooling

Documents