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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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