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HEAT TRANSFER ENHANCEMENTUSING NANO FLUIDS

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Introduction

Preparation methods

Thermal conductivity & viscosity measurement

Effect of various parameters on k

Applications of nanofluids

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Nanofluids are the suspension of ultra-fine metallic or nonmetallic particlesin a base fluids.

Fig: Principle of Nanofluids

TYPES: Metallic nanofluids and Nonmetallic nanofluids

Materials used as nanoparticles include chemically stable metals(e.g.Aluminium, copper)

metal oxides (e.g., alumina, silica, zirconia, titania)

carbon in various forms (e.g., diamond, graphite, carbonnanotubes, fullerene).

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Conventional method to increase heat flux rates:

- extended surfaces such as fins and micro-channels

- increasing flow rates increases pumping power

In 1974 Scientist Norio Taniguchi first used the termNanotechnology.

Choi et al. first prepared nanofluids by mixing nano particles

with base fluids.

In recent years, many researchers have investigated the effectsof nanofluids on the enhancement of heat transfer in thermal

engineering devices.

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PREPARATION METHODS FOR NANOFLUIDS

SINGLE STEP TECHNIQUE:

The single step simultaneously makes and disperses the

nanoparticles directly into a base fluid; Best for metallic nanofluids.

One-step physical method is not suitable for synthesizing

nanofluids in large scale and the cost is also high.

Fig: One-step preparation process of nanofluids

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Nanoparticles was first produced as dry powders anddispersed into the base fluids with the help of ultrasonic

agitation.

Good for oxides nanoparticles.

Most economic method.

To increase the stability, surfactant is also used.

TWO STEP TECHNIQUE:

Fig: Two step preparation process of nanofluids

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TRANSIENT HOT-WIRE METHOD (THW):

Fig: Construction details of test Section

knf=

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Fig: Schematic diagram of experimental setup for measuring CuO nanofluid dynamic viscosity

Fig:Photographic view of Brook field viscometer apparatus

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Hilding et al. conducted this expt. With water-propylene glycol based CuO nanofluid, themeasured viscosity of the CuO nanofluids was observed to be decreasing exponentially with an

increase in the nanofluid temperature .

It can be also observed from the results that the trend in the change of viscosity with temperaturefor all the concentrations of CuO nanofluid is similar.

Fig: Variation of absolute viscosity with the temperature

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The four possible mechanisms in nano fluids which may

contribute to thermal conduction are,

(i) Brownian motion of Nano particles.

(ii) Liquid layering at the liquid/particle interface.

(iii) Ballistic nature of heat transport in nanoparticles.

(iv) Nano particle clustering in Nano fluids.

HEAT CONDUCTION MECHANISMS IN NANOFLUIDS:

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FACTORS INFLUENCING THE THERMAL CONDUCTIVITY OF

NANOFLUIDS:

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EFFECT OF VARIOUS PARAMETERS ON THERMAL

CONDUCTIVITY OF NANOFLUIDS:

TEMPERATURE: PARTICAL SIZE:

Fig:Variation of thermal conductivity of CuO nanofluids withtemperatures for different volume concentrations

Fig: Effect of particle size for CuO in ethylene glycol

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VOLUME CONCENTRATION:

Fig: Effect of volume concentration of SiC in water

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APPLICATIONS OF NANOFLUIDS

Industrial cooling applications

Space and defense vehicles

Solar absorption

Transformer cooling

Transportation

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Nanofluids, i.e., well-dispersed metallic nanoparticles at low volumefractions in liquids, enhance the mixturesthermal conductivity over the

base-fluid values.

Nanofluids provide a promising technical selection for enhancing heat

transfer.

The performance of nanofluid critically depends upon the size, quantity

(volume percentage), shape and distribution of dispersoids, and their

ability to remain suspended.

Development of suitable surfactants for better stability of nanofluids

may be a topic of interest.

Fault free economic production technique is the most important thing

for the commercialization of nanofluids.

CONCLUSIONS

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