Nanofluids Report by jalisantosh

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CONTENTS:

1. INTRODUCTION

2. ABSTRACT

3. LITERATURE REVIEW

4. PREPARATION METHODS FOR NANOFLUIDS

5. THERMAL CONDUCTIVITY OF NANO FLUIDS

6. MATERIALS USED FOR NANOPARTICLES AND

BASE FLUIDS

7. ADVANTAGES OF NANOFLIDS

8. LIMITATION

9. APPLICATION OF NANOFLUIDS

10. CONCLUTION

11. REFERENCES

Department of Mechanical Engineering, MSRITPage 1 of 22

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INTRODUCTION

Nanofluids are engineered colloidal suspensions of nanoparticles in a base fluid.Ingeneral the

size of these nanoparticles vary from 1-100nm.The type of nanoparticleused is directly

dependent on the enhancement of a required property of the basefluid.

All physical mechanisms have a critical length scale, below which the physical properties of

materials are changed. Therefore particles<100 nm exhibit properties that are considerably

deferent from those of conventional solids. The noble properties ofnanophase materials come

from the relatively high surface area to volume ratio that is due to the high proportion of

constituent atoms residing at the grain boundaries. The thermal, mechanical, optical, magnetic,

and electrical properties of nanophasematerials are superior to those of conventional materials

with coarse grain structures.


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ABSTRACT

Suspended nano particles in conventional fluids are called nanofluids. Recent

development of nanotechnology brings out a new heat transfer coolant called ‘nanofluids. these

fluids exhibit larger thermal properties than conventional coolants. Nanofluids can be

considered to be the next-generation heat transfer fluids because they offer exciting new

possibilities to enhance heat transfer performance compared to pure liquids. Micrometer-sized

particle-fluid suspensions exhibit no such dramatic enhancement. Nanofluids are expected to

have superior properties compared to conventional heat transfer fluids, as well as fluids

containing micro-sized metallic particles. The much larger relative surface area of

nanoparticles, compared to those of conventional particles, not only significantly improves heat

transfer capabilities, but also increases the stability of the suspension.


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Literature Review

Nanofluids are suspensions of nanoparticles in a base fluid, typically water. The term

nanoparticle comes from the Latin prefix ‘nano’. It prefix is used to denote the 10-9 part of a

unit. In this context, nano-particles can be termed as the particles with a size in the range of a

few nanometers. Traditionally, nanoparticles have a size between 100-2500 nm. Particles

smaller than 100 nm are termed ultrafine. These objects are being extensively explored due to

their possible applications in medical, optical and electronics fields.

The most popular nano-particles that use to produce nanofluids are: aluminum oxide (Al2O3),

copper (II) oxide (CuO), copper (Cu). Water, oil, decene, acetone and ethylene glycol are the

most common base fluids being used in producing nanofluids.

“Nano-particles can be produced from several processes such as gas

condensation, mechanical attrition or chemical precipitation techniques. Gas

condensation processing has an advantage over other techniques.” (“Critical

Review of heat transfer….,” 2007)


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PREPARATION METHODS FOR NANOFLUIDS

1. TWO-STEP METHOD

Two-step method is the most widely used method for preparing nanofluids.

Nanoparticles,Nanofibers, nanotubes or other nanomaterials used in this method are first

produced as dryPowders by chemical or physical methods. Then the nanosized powder will be

dispersedInto a fluid in the second processing step with the help of intensive magnetic force

agitation,Ultrasonic agitation, high-shear mixing, homogenizing and ball milling. Two-step

method isThe most economic method to produce nanofluids in large scale, because

nanopowderSynthesis techniques have already been scaled up to industrial production levels.

Due to theHigh surface area and surface activity, nanoparticles have the tendency to aggregate.

TheImportant technique to enhance the stability of nanoparticles in fluids is the use

ofSurfactants. However the functionality of the surfactants under high temperature is also aBig

concern, especially for high temperature applications.

2. SINGLE-STEP METHOD

In the single step method the nanoparticles are produced and dispersed

Simultaneously into the base fluid.

Figure: Schematic diagram of nanofluid production Evaporation of materials into low-

vapour-pressure liquids system designed for direct.


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THERMAL CONDUCTIVITY OF NANO FLUIDS

The fluids that have been traditionally used for heat transfer applications have a rather

low thermal conductivity. Taking into account the rising demands of modern technology, it has

been recently proposed that dispersion of small amounts of nanometres-sized solids in the fluid

called nanofluids can enhance the thermal conductivity of the fluids.

• This increase in the thermal conductivity is predicted to be because of the

Following reasons:

1. Brownian motion

2. Interfacial layer (nanolayer)

3. Volume fraction of particles


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Brownian motion

It has been found that the Brownian motion of nanoparticles at the molecular and

nanoscale level is a key mechanism governing the thermal behaviour of nanoparticle–fluid

suspensions ("nanofluids"). The enhancement in the effective thermal conductivity of

nanofluids is due mainly to the localized convection caused by the Brownian movement of the

nanoparticles.

• It is postulated that the enhanced thermal conductivity of a nanofluids, when

Compared to conventional predictions, is mainly due to

• Brownian motion which produces micro-mixing.

• This effect is additive to the thermal conductivity of a static dilute suspension.

• Keff = kstatic + kbrownian

• Since the speed of thermal wave propagation is much faster than the particle

Brownian motion, the static part cannot be neglected


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Fig: Brownian motion of nanoparticles

Interfacial layer (nanolayer)

Although liquid molecules close to a solid surface are known to form Layered

structures, little is known about the connection between this Nanolayer and the thermal

properties of solid/liquid suspensions. It is assumed that the solid-like nanolayer acts as a

thermal bridge between a solid nanoparticle and a bulk liquid and so is key to Enhancing

thermal conductivity. From this thermally bridging nanolayer idea, a structural model of

nanofluids that consists of solid was suggested. Nanoparticles, bulk liquid and solid-like

nanolayers. Conventional pictures of solid/liquid suspensions do not have this nanolayer.The

thermal conductivity of the nanolayer on the surface of the nanoparticle is not known.

However, because the layered molecules are in an intermediate


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Physical state between a bulk liquid and a solid the solid-like nanolayer of liquid molecules

would be expected to lead to a higher thermal Conductivity than that of the bulk liquid.

Fig: Schematic cross section of nanofluids structure consisting of nanoparticles, bulk

liquid, and nanolayers at solid/liquid interface.

Fig: Single spherical particle with interfacial layer in a fluid medium.


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Volume fraction

Highly conductive nanoparticles of very low volume fractions distributed in a quiescent liquid

(called ‘nanofluids’) may measurably increase the effective thermal conductivity of the

suspension when compared to the pure liquid.

Graph: thermal conductivity vs volume fraction


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MATERIALS USED FOR NANOPARTICLES

AND BASE FLUIDS

NANOPARTICLE MATERIALS INCLUDE

Oxide ceramics – Al2O3, CuO

Metal carbides – Sic

Nitrides – AlN, SiN

Metals – Al, Cu

Non-metals – Graphite, carbon nanotubes

Layered – Al + Al2O3, Cu + C

BASE FLUIDS INCLUDE

Water

Ethylene- or tri-ethylene-glycols and other coolants

Oil and other lubricants

Bio-fluids

Polymer solution


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ADVANTAGES OF NANOFLUIDS

High specific surface area and therefore more heat transfer surface between particles

and fluids.

High dispersion stability with predominant Brownian motion of particles.

Reduced pumping power as compared to pure liquid to achieve equivalent heat transfer

intensification.

Reduced particle clogging as compared to conventional slurries, thus promoting system

miniaturization.

Adjustable properties, including thermal conductivity and surface wet ability, by

varying particle concentrations to suit different applications.

LIMITATION

. Lower specific heat

From the literatures, it is found that specific heat of nanofluids is lower than basefluid.

Namburu et al. [28] reported that CuO/ethylene glycol nanofluids, SiO2/ethylene glycol

nanofluids and Al2O3/ethylene glycol nanofluids exhibit lower specific heat compared to

basefluids. An ideal coolant should possess higher value of specific heat which enable the

coolant to remove more heat.


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High cost of nanofluids

Higher production cost of nanofluids is among the Reasons that may hinder the application of

nanofluids in industry. Nanofluids can be produced by either one step or two steps methods.

However both methods require advanced and sophisticated equipments. Lee and Mudawar [24]

and Pantzali etal. stressed that high cost of nanofluids is among the drawback of nanofluids

applications.

Difficulties in production process

Previous efforts to manufacture nanofluids have often employed either a single step that

simultaneously makes and disperses the nanoparticles into base fluids, or a two-step approach

that involves generating nanoparticles and subsequently dispersing them into a base fluid.

Using either of these two approaches, nanoparticles are inherently produced from processes

that involve reduction reactions or ion exchange. Furthermore, the base fluids contain other

ions and reaction products that are difficult or impossible to separate from the fluids. Another

difficulty encountered in nanofluid manufacture is nanoparticles’ tendency to agglomerate into

larger particles, which limits the benefits of the high surface area nanoparticles. To counter this

tendency, particle dispersion additives are often added to the base fluid with the nanoparticles.

Unfortunately, this practice can change the surface properties of the particles, and nanofluids

prepared in this way may contain unacceptable levels of impurities. Most studies to date have

been limited to sample sizes less than a few hundred milliliters of nanofluids. This is

problematic since larger samples are needed to test many properties of nanofluids and, in

particular, to assess their potential for use in new applications


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APPLICATION OF NANOFLUID

This section explains applications of nanofluids in industrial, commercial, residential

and transportation sectors based on available literatures.

HEAT TRANSFER INTENSIFICATION

Since the origination of the nanofluids concept about a decade ago, the potentials of

nanofluids in heat transfer applications have attracted more and more attention. Up to now,

there are some review papers, which present overviews of various aspects of nanofluids

including preparation and characterization, techniques for the measurements of thermal

conductivity, theory and model, thermo physical properties, convective heat transfer. In this

part, we will summarize the applications of nanofluids in heat transferEnhancement.

ELECTRONIC APPLICATIONS

Due to higher density of chips, design of electronic components with more compact

makes heat dissipation more difficult. Advanced electronic devices face thermal management

challenges from the high level of heat generation and the reduction of available surface area for

heat removal. So, the reliable thermal management system is vital for the smooth operation of

the advanced electronic devices. In general, there are two approaches to improve the heat

removal for electronic equipment. One is to find an optimum geometry of Cooling devices;

another is to increase the heat transfer capacity. Recent researches illustrated that nanofluids

could increase the heat transfer coefficient by increasing the thermal conductivity of a coolant.

Jang et al. designed a new cooler, combined micro channel Heat sink with nanofluids. Higher

cooling performance was obtained when compared to the device using pure water as working

medium. Nanofluids reduced both the thermal resistance and the temperature difference

between the heated micro channel wall and the coolant. A combined micro channel heat sink

with nanofluids had the potential as the next generation cooling devices for removing ultra-

high heat flux. Nguyen et al. designed a closed liquid-circuit to investigate the heat transfer

enhancement of a liquid cooling system, By replacing the base fluid (distilled water) with a

nanofluid composed of distilled water and Al2O3 nanoparticles at various concentrations.

Measured data have clearly shown that the inclusion of nanoparticles within the distilled water

has produced a considerable enhancement in convective heat transfer coefficient of the cooling


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block. With particle loading 4.5 vol%, the enhancement is up to 23% with respect to that of the

base fluid. It has also been observed that an augmentation of particle concentration has

produced a clear decrease of the junction temperature between the heated component and the

cooling block. Silicon micro channel heat sink performance using nanofluids containing Cu

nanoparticles was analyzed. It was found nanofluids could enhance the performance as

compared with that using pure water as the coolant. The enhancement was due to the increase

in thermal conductivity of coolant and the nanoparticle thermal dispersion effect. The other

Advantage was that there was no extra pressure drop since the nanoparticle was small and

particle volume fraction was low. The thermal requirements on the personal computer become

much stricter with the increase in thermal dissipation of CPU. One of the solutions is the use of

heat pipes. Nanofluids, employed as working medium for conventional heat pipe, have shown

The suspended nanoparticles tend to bombard the vapour bubble during The bubble formation.

Therefore, it is expected that the nucleation size of vapour bubble is much smaller for fluid

with suspended nanoparticles than that without them. This may be the major reason for

reducing the thermal resistance of heat pipe.. For example, at the input power of 80.0 W,

diamond nanofluid could reduce the temperature difference between the evaporator and the

condenser from 40.9 to 24.3°C. This study would accelerate the development of a highly

efficient cooling device for ultrahigh-heat-flux electronic systems. The thermal performance

investigation of heat pipe indicated that nanofluids containing silver or titanium nanoparticles

could be used as an efficient cooling fluid for devices with high energy density. For a silver

nanofluid, the Temperature difference decreased 0.56-0.65℃ compared to water at an input

power of 30-50 W. For the heat pipe with titanium nanoparticles at a volume concentration of

0.10%, the thermal efficiency is 10.60% higher than that with the based working fluid. These

positive results are promoting the continued research and development of nanofluids for such

applications.

TRANSPORTATION

Nanofluids have great potentials to improve automotive and heavy-duty engine cooling

rates by increasing the efficiency, lowering the weight and reducing the complexity of thermal

management systems. The improved cooling rates for automotive and truck engines can be

used to remove more heat from higher horsepower engines with the same size of cooling

system. Alternatively, it is beneficial to design more compact cooling system with smaller and


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lighter radiators. It is in turn benefit the high performance and high fuel economy of car and

truck. Ethylene glycol based nanofluids have attracted much attention in the application as

engine coolant due to the low-pressure operation compared with a 50/50 mixture of ethylene

glycol and water, which is the nearly universally used automotive coolant. The nanofluids has a

high boiling point, and it can be used to increase the normal coolant operating temperature and

then reject more heat through the existing coolant system . The experimental platform was the

transmission of a four-wheel drive vehicle. The used nanofluids were prepared by dispersing

Cut and Al2O3 nanoparticles into engine transmission oil. The results showed that

CuOnanofluids produced the lower transmission temperatures both at high and low rotating

speeds. From the thermal performance viewpoint, the use of nanofluid in the transmission has a

clear advantage. The researchers of Argonne National Laboratory have assessed the

applications of nanofluids for transportation. The use of high-thermal conductive nanofluids in

radiators can lead to a reduction in the frontal area of the radiator up to 10%. The fuel saving is

up to 5% due to the reduction in aerodynamic drag. It opens the door for new aerodynamic

automotive designs that reduce emissions by lowering drag. The application of nanofluids also

contributed to a reduction of friction and wear, reducing parasitic losses, operation of

components such as pumps and compressors, and subsequently leading to more than 6% fuel

savings. In fact, nanofluids not only enhance the efficiency and economic performance of car

engine, but also will greatly influence the structure design of automotives. For example, the

engine radiator cooled by a nanofluid will be smaller and lighter. It can be placed elsewhere in

the vehicle, allowing for the redesign of a far more aerodynamic chassis. By reducing the size

and changing the location of the radiator, a reduction in weight and wind resistance could

enable greater fuel efficiency and subsequently lower exhaust emissions. Computer simulations

from the US department of energy’s office of vehicle technology showed that nanofluid

coolants could reduce the size of truck radiators by 5%. This would result in a 2.5% fuel saving

at highway speeds.

INDUSTRIAL COOLING APPLICATIONS

The application of nanofluids in industrial cooling will result in great energy savings

and emissions reductions. For US industry, the replacement of cooling and heating water with

nanofluids has the potential to conserve 1 trillion Btu of energy. For the US electric power

industry, using nanofluids in closed loop cooling cycles could save about 10-30 trillion Btu per


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year (equivalent to the annual energy consumption of about 50,000–150,000 households). The

associated emissions reductions would be approximately 5.6 millionMetric tons of carbon

dioxide, 8,600 metric tons of nitrogen oxides, and 21,000 metric tons of sulphur dioxide.

Experiments were performed using a flow-loop apparatus to explore the performance of

polyalphaolefinnanofluids containing exfoliated graphite nanoparticle fibres in cooling. It was

observed that the specific heat of nanofluids was found to be 50% higher for nanofluids

compared with polyalphaolefin and it increased with temperature. The thermalDiffusivity was

found to be 4 times higher for nanofluids. The convective heat transfer was enhanced by ~10%

using nanofluids compared with using polyalphaolefin. Ma et al proposed the concept of nano

liquid-metal fluid, aiming to establish an engineering route to make the highest conductive

coolant with about several dozen times larger thermal conductivity than that of water. The

liquid metal with low melting point is expected to be an idealistic base fluid for making super

conductive solution which may lead to the ultimate coolant in a wide variety of heat transfer

enhancement area. The thermal conductivity of the liquid-metal fluid can be enhanced through

the addition of more Conductive nanoparticles.

HEATING BUILDINGS AND REDUCING POLLUTION

Nanofluids can be applied in the building heating systems. Kulkarni et al. evaluated

how they perform heating buildings in cold regions. In cold regions, it is a common practice to

use ethylene or propylene glycol mixed with water in different proportions as a heat transfer

fluid. So 60:40 ethylene glycol/water (by weight) was selected as the base fluid. The results

showed that using nanofluids in heat exchangers could reduce volumetric and mass flow rates,

resulting in an overall pumping power savings. Nanofluids necessitate smaller heating systems,

which are capable of delivering the same amount of thermal energy as larger heating systems,

but are less expensive this lowers the initial equipment cost excluding nanofluids cost. This

will also reduce environmental pollutants because smaller heating units use less power, and the

heat transfer unit has less liquid and material waste to discard at the end of its life cycle.


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NUCLEAR SYSTEMS COOLING

The Massachusetts Institute of Technology has established an interdisciplinary centre for

nanofluids technology for the nuclear energy industry. The researchers are exploring the

nuclear applications of nanofluids, specifically the following three: 1) main reactor coolant for

pressurized water reactors (PWRs). It could enable significant power up rates in current and

future PWRs, thus enhancing their economic performance. Specifically, the use of nanofluids

with at least 32% higher critical heat flux (CHF) could enable a 20% power density up rate in

current plants without changing the fuel assembly design and without reducing the margin to

CHF; 2) coolant for the emergency core cooling systems (ECCSs) of Both PWRs and boiling

water reactors. The use of a nanofluids in the ECCS accumulators and safety injection can

increase the peak-cladding-temperature margins (in the nominal-power core) or maintain them

in up rated cores if the nanofluids has a higher post-CHF heat transfer rate; 3) coolant for in-

vessel retention of the molten core during severe accidents in high-power- density light water

reactors. It can increase the margin to vessel breach by 40% during severe accidents in high-

power density systems such as Westinghouse APR1000 and the Korean APR1400. While there

exist several significant gaps, including the nanofluids thermal-hydraulic performance at

prototypical reactor conditions and the compatibility of the nanofluids chemistry with the

reactor materials. Much work should be done to overcome these gaps before any applications

can be implemented in a nuclear power plant.

SPACE AND DEFENCE

Due to the restriction of space, energy and weight in space station and aircraft, there is a

strong demand for high efficient cooling system with smaller size. You et al. And Vassalo et al.

have reported order of magnitude increases in the critical heat flux in pool

Boiling with nanofluids compared to the base fluid alone. Further research of nanofluids will

lead to the development of next generation of cooling devices that incorporate nanofluids for

ultrahigh-heat-flux electronic systems, presenting the possibility of raising chip power in

electronic components or simplifying cooling requirements for space applications. A number of

military devices and systems require high-heat flux cooling to the level of tens of MW/m2. At

this level, the cooling of military devices and system is vital for the reliable operation.


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Nanofluids with high critical heat fluxes have the potential to provide the required cooling in

such applications as well as in other military systems, including military vehicles, submarines,

and high-power laser diodes. Therefore, nanofluids have wide application in space and defence

fields where power density is very high and the components should be smaller and weight less

Cancer Theraupetics

There is a new initiative which takes advantage of several properties of certain nanofluids to use in cancer imaging and drug delivery. This initiative involves the use of iron-based nanoparticles as delivery vehicles for drugs or radiation in cancer patients. Magnetic nanofluids are to be used to guide the particles up the bloodstream to a tumor with magnets. It will allow doctors to deliver high local doses of drugs or radiation without damaging nearby healthy tissue, which is a significant side effect of traditional cancer treatment methods. In addition, magnetic nanoparticles are more adhesive to tumor cells than non-malignant cells and they absorb much more power than microparticles in alternating current magnetic fields tolerable in humans; they make excellent candidates for cancer therapy.

Magnetic nanoparticles are used because as compared to other metal-type nanoparticles, these provide a characteristic for handling and manipulation of the nanofluid by magnetic force [41]. This combination of targeted delivery and controlled release will also decrease the likelihood of systemic toxicity since the drug is encapsulated and biologically unavailable during transit in systemic circulation. The nanofluid containing magnetic nanoparticles also acts as a super-paramagnetic fluid which in an alternating electromagnetic field absorbs energy producing a controllable hyperthermia. By enhancing the chemotherapeutic efficacy, the hyperthermia is able to produce a preferential radiation effect on malignant cells [42].There are numerous biomedical applications that involve nanofluids such as magnetic cell separation, drug delivery, hyperthermia, and contrast enhancement in magnetic resonance imaging. Depending on the specific application, there are different chemical syntheses developed for various types of magnetic nanofluids that allow for the careful tailoring of their properties for different requirements in applications. Surface coating of nanoparticles and the colloidal stability of biocompatible water-based magnetic fluids are the two particularly important factors that affect successful application [43, 44].

.

For most biomedical uses the magnetic nanoparticles should be below 15 nm in size and stably dispersed in water. A potential magnetic nanofluid that could be used for biomedical applications is one composed of FePt nanoparticles. This FePtnanofluid possesses an intrinsic chemical stability and a higher saturation magnetization making it ideal for biomedical applications. However, before magnetic nanofluids can be used as drug delivery systems, more


http://www.hindawi.com/journals/ame/2010/519659/#B24




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research must be conducted on the nanoparticles containing the actual drugs and the release mechanism.

Cooling of Microchips

A principal limitation on developing smaller microchips is the rapid heat dissipation. However, nanofluids can be used for liquid cooling of computer processors due to their high thermal conductivity. It is predicted that the next generation of computer chips will produce localized heat flux over 10 MW/, with the total power exceeding 300 W. In combination with thin film evaporation, the nanofluid oscillating heat pipe (OHP) cooling system will be able to remove heat fluxes over 10 MW/and serve as the next generation cooling device that will be able to handle the heat dissipation coming from new technology So as to obtain experimental data while maintaining the integrity of the OHP system, Arif employed neutron imaging to study the liquid flow in a 12-turn nanofluid OHP. As a consequence of the high intensity neutron beam from an amorphous silicon imaging system, they were able to capture dynamic images at 1/30th of a second. The nanofluid used was composed of diamond nanoparticles suspended in water.

Even though nanofluids and OHPs are not new discoveries, combining their unique features allows for the nanoparticles to be completely suspended in the base liquid increasing their heat transport capability. Since nanofluids have a strong temperature-dependent thermal conductivity and they show a nonlinear relationship between thermal conductivity and concentration, they are high performance conductors with an increased CHF. The OHP takes intense heat from a high-power device and converts it into kinetic energy of fluids while not allowing the liquid and vapor phases to interfere with each other since they flow in the same direction.

However, as the heat input increases, the oscillating motion increases and the resultant temperature difference between the evaporator and condenser does not continue to increase after a certain power input. This phenonmenon inhibits the effective thermal conductivity of the nanofluid from continuously increasing. However, at its maximum power level of 336 W, the temperature difference for the nanofluid OHP was still less than that for the OHP with pure water, Figure 2. Hence, it has been shown that the nanofluid can significantly increase the heat transport capability of the OHP.


http://www.hindawi.com/journals/ame/2010/519659/fig2/

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Lin et al. investigated nanofluids in pulsating heat pipes by using silver nanoparticles, and discovered encouraging results. The silver nanofluid improved heat transfer characteristics of the heat pipes.Nguyen et al. investigated the heat transfer enhancement and behavior of -water nanofluid with the intention of using it in a closed cooling system designed for microprocessors or other electronic devices. The experimental data supports that the inclusion of nanoparticles into distilled water produces a significant increase of the cooling convective heat transfer coefficient. At a given particle concentration of 6.8%, the heat transfer coefficient increased as much as 40% compared to the base fluid of water. Smaller nanoparticles also showed higher convective heat transfer coefficients than the larger ones.

Further research of nanofluids in electronic cooling applications will lead to the development of the next generation of cooling devices that incorporate nanofluids for ultrahigh-heat-flux electronic systems.


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ENERGY APPLICATIONS

Energy storage

Solar absorption

MECHANICAL APPLICATIONS

Friction reduction

Magnetic sealing

Nanocryosurgery

BIOMEDICAL APPLICATION

Antibacterial activity

Nanodrug delivery

OTHER APPLICATIONS

Intensify micro reactors

Nanofluids as vehicular brake fluids

Nanofluids based microbial fuel cell

Nanofluid detergents


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CONCLUSIONS

Downscaling, or miniaturization, has been the major trend in modern science and

technology. Stable suspensions of carbon nanotubes, oxide and metallic nanoparticles in

conventional heat transfer fluids can be achieved by maintaining the particle size below a

threshold level. Studies of nanofluids reveals high thermal conductivities and heat transfer

coefficients compared to those of conventional fluids.

Nanofluids are important because they can be used in numerous applications involving heat transfer, and other applications such as in detergency. Colloids which are also nanofluids have been used in the biomedical field for a long time, and their use will continue to grow. Nanofluids have also been demonstrated for use as smart fluids. Problems of nanoparticle agglomeration, settling, and erosion potential all need to be examined in detail in the applications. Nanofluids employed in experimental research have to be well characterized with respect to particle size, size distribution, shape and clustering so as to render the results most widely applicable. Once the science and engineering of nanofluids are fully understood and their full potential researched, they can be reproduced on a large scale and used in many applications. Colloids which are also nanofluids will see an increase in use in biomedical engineering and the biosciences.

Further research still has to be done on the synthesis and applications of nanofluids so that they may be applied as predicted. Nevertheless, there have been many discoveries and improvements identified about the characteristics of nanofluids in the surveyed applications and we are a step closer to developing systems that are more efficient and smaller, thus rendering the environment cleaner and healthier.


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