HEAT TRANSFER ENHANCEMENT USING NANO FLUIDS

HEAT HEA T TRANSFER ENHANCEME ENHANCEMENT NT USING NANO FLUIDS

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Introduction

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Preparation methods

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 Thermal conductivity & viscosity measurement

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Effect of various parameters on „k‟

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Applications of nanofluids

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

Fig: Principle of Nanofluids 

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TYPES: Metallic nanofluids and Nonmetallic nanofluids Materials used as nanoparticles include chemically stable Aluminium, copper) metal oxides (e.g., alumina, silica, zirconia, titania) carbon in various forms (e.g., diamond, graphite, nanotubes, fullerene).

metals(e.g.

carbon

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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

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In 1974 Scientist Norio Taniguchi first used the term “Nanotechnology”.

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Choi et al. first prepared nanofluids by mixing nano particles with base fluids.

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In recent years, many researchers have investigated the effects of nanofluids on the enhancement of heat transfer in thermal engineering devices.

PREPARATION METHODS FOR NANOFLUIDS

SINGLE STEP TECHNIQUE:

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Fig: One-step preparation process of nanofluids

 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.

TWO STEP TECHNIQUE:

Fig: Two step preparation process of nanofluids

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Nanoparticles was first produced as dry powders and dispersed 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.

 TRANSIENT HOT-WIRE METHOD (THW):

Fig: Construction details of test Section

knf =

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

Fig: Variation of absolute viscosity with the temperature 

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Hilding et al. conducted this expt. With water-propylene glycol based CuO nanofluid, the measured 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 temperature for all the concentrations of CuO nanofluid is similar.

HEAT CONDUCTION MECHANISMS IN NANOFLUIDS:

 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.

FACTORS INFLUENCING THE THERMAL CONDUCTIVITY OF NANOFLUIDS:

EFFECT OF VARIOUS PARAMETERS CONDUCTIVITY OF NANOFLUIDS:

 TEMPERATURE:

Fig:  V ariation of thermal conductivity of CuO nanofluids with temperatures for different volume concentrations

ON

THERMAL

PARTICAL SIZE:

Fig: Effect of particle size for CuO in ethylene glycol

 VOLUME CONCENTRATION:

Fig: Effect of volume concentration of SiC in water

APPLICATIONS OF NANOFLUIDS

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Industrial cooling applications

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Space and defense vehicles

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Solar absorption

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 Transformer cooling

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 Transportation

CONCLUSIONS

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Nanofluids, i.e., well-dispersed metallic nanoparticles at low volume fractions in liquids, enhance the mixture‟s thermal conductivity over the base-fluid values.

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Nanofluids provide a promising technical selection for enhancing heat transfer.

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 The performance of nanofluid critically depends upon the size, quantity (volume percentage), shape and distribution of dispersoids, and their ability to remain suspended.

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Development of suitable surfactants for better stability of nanofluids may be a topic of interest.

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Fault free economic production technique is the most important thing for the commercialization of nanofluids.