Research for Nano-coolants, A Review

1. Summary of
“ Nano fluid as a coolant in automobile radiator”
Source : International Journal of Scientific and Research Publications,Volume 3, Issue8,August 2013 1 ISSN 2250 -
3153
In automotive systems, heatexchangersaveryvital role.The improvedheattransfermethodscould
leadto smallerheatexchangerswhichinturnreduce weightof the vehicleandimprove mileage.The
heatflowcan be increasedbyincreasingthe temperature differenceandincreasingheattransferarea.
In automotive systems, the heattransferareacanonlybe increasedbyincreasingsize of the heat
exchanger,whichwillfurtherleadtoincrease inthe weight. Heattransfercanalsobe increase by
increasingthe heattransfercoefficient‘h’.
The heat transfersystemswhichemployforcedconvectionof gasforheattransferexhibitgreaterheat
transfercoefficientthansystemswhichemployfree convectionof gas.Additiveslike glycolare often
addedincoolantto depressthe freezingpointof the coolantandincrease the boilingpointof the
coolant.
Nanofluidscanalsobe usedinautomobilestocool engines.The nanofluidcoolantcanalsoflow
throughtinypassagesinMEMS to improve itsefficiency.A “nanofluid”consistingof coppernanometer-
sizedparticlesdispersedinethyleneglycol hasamuch highereffectivethermal conductivitythaneither
pure ethylene glycolorethylene glycol containingthe same volume fractionof dispersedoxide nano
particles.Thermal conductivityof ethylene glycol canbe increasedby40 % fora nano fluidsconsistingof
ethylene glycol containingapproximately0.3vol % Cu nano particlesof meandiameter<10nm. A nano
fluidconsistingof Copperoxide (CuO) andIronoxide (Fe2O3) nanoparticlesdispersedinwaterhas
much higherheattransfercoefficientthanpure water. The nanofluidsshow greateroverall heat
transfercoefficientincomparisonwithwaterupto 9%. The thermal conductivityof CuO/waternano
fluidsismuchhigherthanthat of base fluidwater.Eventhe heattransfercoefficientincreases. The
higherthermal conductivityandlargersurface areaof copper nano particlesare attributedtothis
improvement.Itisalsonotedthatthermal conductivityincreaseswithparticlesvolume fractionbut
decreaseswithelapsedtime. The thermal conductivityof nano fluidsisaffectedbypHlevel andaddition
of surfactantduringnano fluidspreparationstage.
Thermal conductivity notonly depend onthe nano particlesconcentrationbutalsoonthe temperature.
So itwill be more beneficial if nano fluidsare usedinhightemperature applications.The nanofluids
provide higherthermal conductivitycomparedtobase fluids.Itsvalue increaseswithparticles
concentration.Temperature,particlessize, dispersionandstabilityalso playimportantrole in
determiningthermal conductivityof nano fluids.Lubricatingoilswithnano particlesadditives(MoS2,
CuO,TiO2, diamond,etc.) exhibitimprovedload-carryingcapacity,anti-wearandfriction-reduction
properties. These featuresmade nano fluidsveryattractiveinsome coolingand/orlubricating
applicationinmanyindustriesincludingmanufacturing,transportation,energy,andelectronics,etc.

2. To improve automotiveandheavy-dutyengine coolingrates byincreasingthe efficiency,loweringthe
weightandreducingthe complexityof thermal managementsystem, the automotiveandtruckengines
can be usedtoremove more heatfromhigherhorsepowerengineswiththe same size of cooling
system.Alternatively, itisbeneficialtodesignmore compactcoolingsystemwithsmallerandlighter
radiators,in turn benefitthe highperformance andhighfuel economyof car andtruck. Ethylene glycol
basednano fluidshave attractedmuchattentioninthe applicationasengine coolant. The reductionof
frictionandwear,reductioninparasiticlosses,operationof componentssuchaspumpsand
compressors,andsubsequentlyleadingtomore than6% fuel savings,so greaterimprovementof
savingscouldbe obtainedinthe future bythe use of nano fluids. Noerosionisobservedinnanofluids
made frombase fluidsethylene andtri-chloroethyleneglycolsbutnanofluidsmade fromcoppershows
erosion.The coppernano fluidproducesahigherwearrate than the base fluidandthisispossiblydue
to oxidationof coppernano particles.A lowerwearandfrictionrate wasseenforaluminanano fluidsin
comparisontothe base fluid.
Because of higherthermal diffusivityof nano fluids,the thermal signalvariationsforknockdetection
increasedby15% overthat predictedusingwateralone.The additionof nano particlestothe standard
engine coolanthasthe potential toimprove automotiveandheavy-dutyengine coolingrates.Such
improvementcanbe usedto remove engine heatwithareduced-size coolantsystem.Smallercoolant
systemsresultinsmallerandlighterradiators,whichinturnbenefitalmosteveryaspectof car and
economy.Thismayreduce the coefficientof dragand thusresultinginlessfuel consumption.
Alternatively,improvedcoolingratesforautomotive andtruckenginescanbe usedtoremove more
heatfrom higherhorsepowerengineswiththe same size of coolantsystem. Pure ethylene glycol isa
poor heattransferfluidcomparedtoa 50-50 mixture of ethyleneglycol andwater.The mostprominent
isthe lowpressure operationof anethylene-glycol-basednanofluidscomparedwitha50/50 mixture of
ethylene glycol andwater.Thisnano fluidalsohasa highboilingpoint,whichisdesirable for
maintainingsingle-phase coolantflow.
A higherboilingpoint coolant can be usedto increase the normal coolant operating temperature and
then rejectmore heatthrough the existingcoolant system.More heat rejectionallowsa variety of
designenhancementsincludingengineswithhigherhorsepower.The more concentrations of the
nano particles,the more enhancementofthe engine heatdissipatingcapacity. Whenthe
concentration reached5%, the heat dissipatingcapacity increasedby 44.1%. With a remarkable
enhancementonheat-transfercapability, the workload of the pump of engine coolingsystemonly
increasedby 6%, which could be acceptable. The trend toward higherengine powerand EGR
inevitablyleadsto larger radiators and increasedfrontal areas, resultinginadditional aerodynamic
drag and increasedfuel consumption.Therefore,coolingisone of the top technical challenges facing
the truck industry.
The limitationsofexistingtechnologiesasfollows:
• Liquid-side:traditional coolantsand oilshave inherentlypoorheat transfer properties.

3. • Air-side:currentradiator designsfor increasingair-side heattransfer have already adopted
extendedsurface technologyto its limits.
But nano fluidsdo not show considerable improvementinheattransfer whenused withcurrent
radiator designs.
A car engine coolant (Al2O3 nano fluid) usinga standard car engine coolant (HP KOOLGARD) as the
base fluid,and studiedthe thermal conductivityand viscosityof the coolant. The prepared nano fluid,
containingonly 3.5% volume fraction of Al2O3 nano particles,displayeda fairlyhigher thermal
conductivitythan the base fluid,and a maximumenhancementof 10.41% of thermal conductivitywas
observedat room temperature.
The longterm stability of nano particlesdispersionisone ofthe basic requirementsofnano fluids
applicationsbut thermal conductivityof ethylene glycol basednano fluidsand nano particles
decreaseswithtime. Freshnano fluidsexhibitedslightlyhigherthermal conductivitiesthannano
fluidsthat were storedup to two months. Long term degradationin thermal performance of nano
fluidscan happen. Particlessettlingmust be examinedcarefullysince it may lead to cloggingof
coolant passages. To overcome particlessettlingwe can use surfactant but the excessquantity of
surfactant has a harmful effecton viscosity,thermal property,chemical stability,and thus it is
strongly recommendedtocontrol the additionof the surfactant with great care. However,the
additionof surfactant wouldmake the particle surface coated, therebyresultinginthe screening
effecton the heat transfer performance of nano particles.
The coolants with higherdensityand viscosityexperience higherpressure drop.This has contributed
to the disadvantagesof nano fluidsapplicationas coolant liquids.The viscosity and densityof nano
fluidsis higherthan the base fluids.The pressure drop and pumpingpowerincreasesin case of a nano
fluid. For a givenheat duty, the requiredvolumetricFlow rates for both the water and the nano fluid
are practically equal,while the necessarypumpingpower in the case of the nano fluidis up to two
timeshigherthan the correspondingvalue for water due to the higher kinematicviscosityof the fluid.
No convective heattransfer improvementwas noticedfor amorphous carbonic nano fluidsin
turbulentflow despite 8% improvementin laminar flow,so substitutionof conventional coolantsby
nano fluidsseemedbeneficial forlaminarflowcompared to turbulent flow.An ideal coolant should
possesshighervalue of specificheat which enablesthe coolant to remove more heat, but the specific
heat of nano fluidis lesserthan the base fluid.
Even the cost ofmanufacture of nano fluidsis quite high incontrast to base fluid.So to use nano
fluids,we have to find itseconomical manufacturing techniques.We have to discovervarious ways to
improve their longterm stabilityalso.