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Int. J. Mech. Eng. & Rob. Res. 2014 Aadarsh Mishra, 2014

ANALYSIS OF NANOFLUIDS

Aadarsh Mishra1*

*Corresponding Author: Aadarsh Mishra,aadarshm9@gmail.com

A colloidal mixture of nano-sized particles in a base liquid called nanofluid, which is the newgeneration of heat transfer fluid for various heat transfer applications with enhanced thermophysical properties and heat transfer performance can be applied in many devices for betterperformances. Specific application of nanofluids in engine cooling, solar water heating, coolingand heating in buildings and cooling of heat exchanging devices have been discussed. Moreover,challenges and future directions of other applications of nanofluids have been presented in thispaper.

Keywords: Nano fluids, Nano sized particles

INTRODUCTIONTo take care of growing demand of energydensity, the miniaturized devices as well aslarge devices require more efficient coolingsystems with greater cooling capacities anddecreased sizes. Thus heat transfer capacityneeds to be increase and this need must bemet in two ways: introducing new designs, suchas microchannels and introducing extendedsurface heat exchanger, and enhancing theheat transfer capability of the fluid itself.Successful employment of nanofluids willsupport the current trend toward componentminiaturization. The thermal conductivities ofthe particle materials are typically an order-of-magnitude higher than those of the base fluidssuch as water, ethylene glycol, and light oils,

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Int. J. Mech. Eng. & Rob. Res. 2014

1 Department of Mechanical Engineering, Manipal Institute of Technology, Manipal University, Manipal, Karnataka 576104, India.

and nanofluids, even at low volumeconcentrations, resulting in significantincreases in thermal performance. Properlyengineered nanofluids possess the followingadvantages: (i) High specific surface area andtherefore more heat transfer surface betweenparticles and fluids. (ii) High dispersion stabilitywith predominant Brownian motion ofparticles, (iii) Reduced pumping power ascompared to pure liquid to achieve equivalentheat transfer intensification, (iv) Reducedparticle clogging as compared to conventionslurries, thus promoting system miniaturization,(v) Adjustable properties, including thermalconductivity and surface wettability, by varyingparticle concentrations to suit differentapplications. The above potentials provided

Research Paper

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Int. J. Mech. Eng. & Rob. Res. 2014 Aadarsh Mishra, 2014

the thrust necessary to begin research innanofluids, with the expectation that thesefluids will play an important role in developingthe next generation of cooling technology.Nanofluids have the potential to reduce thermalresistances, and industrial groups that wouldbenefit from such improvement, includetransportation, electronics, medical, food, andmanufacturing.

APPLICATIONS OFNANOFLUIDSEngine CoolingVehicle thermal management is a crosscuttingtechnology because it directly or indirectlyaffects engine performance, fuel economy,safety and reliability, aerodynamics, driver/passenger comfort, materials selection,emissions, maintenance, and component life.The heat rejection requirements of automobilesand trucks are continually increasing due totrends toward more power output. An ethyleneglycol and water mixture, the nearly universallyused automotive coolant, is a relatively poorheat transfer fluid compared to water alone.Engine oils perform even worse as a heattransfer medium. The addition of nanoparticlesto the standard engine coolant has thepotential to improve automotive and heavy-duty engine cooling rates. Smaller coolantsystems result in smaller and lighter radiators,which in turn benefit almost every aspect ofcar and economy. This may reduce thecoefficient of drag and thus resulting in lessfuel consumption. Alternatively, improvedcooling rates for automotive and truck enginescan be used to remove more heat from higherhorsepower engines with the same size ofcoolant system.

Heat ExchangerCooling is one of the important challengesfaced by many industries. The conventionalway to increase cooling rates is increasing theheat transfer area. There is a balance betweenpumping costs and heat transfer. Furtherincrease of heat transfer area requiresincreasing the size of thermal managementsystem.Nanotechnology may help acceleratethe development of energy-efficient centralheating. When added to water, CNTs disperseto form a nanofluid. Researchers havedeveloped Nanofluids whose rates of forcedconvective heat transfer are four times betterthan the norm by using CNTs. When added toa home’s commercial water boiler, suchNanofluids could make the central heatingdevice 10% more efficient . The newexperimental data concerning the use ofNanofluids in a commercial heat exchangerconfirmed that, besides the physicalproperties, the type of flow (laminar or turbulent)inside the heat exchanging equipment playsan important role in the effectiveness of ananofluid. When the heat exchangingequipment operates under conditions thatpromote turbulence, the use of nanofluids isbeneficial if and only if the increase in theirthermal conductivity is accompanied by amarginal increase in viscosity, which seemsvery difficult to be achieved. On the other hand,if the heat exchanger operates under laminarconditions, the use of nanofluids seemsadvantageous, the only disadvantages so farbeing their high price and the potentialinstability of the suspension. In conclusion, inindustrial heat exchangers, where largevolumes of Nanofluids are involved andturbulent flow is usually developed, thesubstitution of conventional fluids by Nanofluids

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Int. J. Mech. Eng. & Rob. Res. 2014 Aadarsh Mishra, 2014

seems inauspicious. However, in micro-scaleequipment with increased thermal duties,where also volume is a matter, and especiallyin laminar flow, the use of a nanofluid insteadof a conventional fluid seems advantageous.In each case the nanofluid properties shouldbe defined carefully in order to evaluate itsefficacy in a specific heat exchanger. Thebenefits of nanofluid cooling are clear, includingdramatic enhancement of cooling rates whileoperating the advanced cooling system atroom temperature. Furthermore, the possibilityof thermal distortion and flow-induced vibrationwill be eliminated by passing the Nanofluidsthrough micro channels within the silicon mirroritself. Future experimental work on thenanofluid cooled microchannel heat exchangerwill advance the art of cooling high-heat-loadX-ray monochromators.

CHALLENGES OFNANOFLUIDSThe use of Nanofluids in a wide variety ofapplications appears promising. But thedevelopment of the field is hindered by:

• Lack of agreement of results obtained bydifferent researchers.

• Poor characterization of suspensions.

• Lack of the mechanisms responsible forchanges in properties.

Long Term Stability ofNanoparticles DispersionPreparation of homogeneous suspensionremains a technical challenge since thenanoparticles always form aggregates due tovery strong vander Waals interactions. To getstable Nanofluids, physical or chemicaltreatment have been conducted such as an

addition of surfactant, surface modification ofthe suspended particles or applying strongforce on the clusters of the suspendedparticles.

Generally, long term stability of nanoparticles dispersion is one of the basicrequirements of nanofluids applications.Stability of nanofluids have goodcorresponding relationship with theenhancement of thermal conductivity where thebetter dispersion behavior, the higher thermalconductivity of Nanofluids.

Higher ViscosityThe viscosity of nanoparticles-watersuspensions increases in accordance withincreasing particle concentration in thesuspension. So, the particle mass fractioncannot be increased unlimitedly.

CONCLUSIONIt has been found that the improved thermalconductivities of nanofluids are the one of thedriving factors for better performance indifferent applications. It was observed thatthere are inconsistencies in the resultspublished in open literature by manyresearchers. Few researchers’ reported theinconsistencies between model andexperimental results of thermal conductivity ofnanofluids. The proper physical mechanism ofheat transfer enhancement has not beenestablished till date. It is clear that the increaseof thermal conductivity might be offset by theincrease of viscosity, the decrease of effectivespecific heat of nanofluid.

Nanofluids stability and its production costare major factors that hinder thecommercialization of Nanofluids. By solving

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these challenges, it is expected that nanofluidscan make substantial impact as coolant in heatexchanging devices.

ACKNOWLEDGMENTI would also like to dedicate this research workto my father late R S Mishra and mother K LMishra.

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