seminar.pptx 5

7/31/2019 Seminar.pptx 5

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Introduction

Nanostructure

Preparation of nano fluids

Scientific Analysis of Al2O3 based nanofluids

Application of nanofluids

Advantages

Disadvantages

Conclusion

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Heat transfer in cooling processes can be found in many industrialareas.

The conventional methods to increase cooling rates:1- Extended surfaces such as fins2- Increasing flow rates

These conventional methods have their own limitations:1- Fins: undesirable increase in the size of thermal management

system2- Increasing flow rates: increases pumping power

There is an immediate need for new and innovative concepts toachieve ultra high performance cooling.

Nanofluids are promising to meet and enhance the challenges.3


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Nano fluids are a relatively new class of fluids

which consist of a base fluid with nano -sized

particles (1100 nm) suspended within them.

The thermal conductivities of particle material is

higher as compared to base fluids.

A nano fluid is the suspension of nano particles ina base fluid.

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NANO FLUIDS:

Nano fluids have a potential to reduce such problems

Nanofluids, a name conceived by Dr. Choi, in Argonne National

Laboratory, to describe a fluid consisting of solid nanoparticles with

size less than 100 nm suspended on it with solid volume fractions

typically less than 4%.

Fig 1. magnified view 5


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MATERIALSFOR NANOPARTICLES

AND BASE FLUIDS:Materials for nanoparticles and base fluids are diverse:

1. Nanoparticle materials include:

Oxide ceramics Al2O3, CuO

Metal carbides SiC Nitrides AlN, SiN

Metals

Al, Cu Nonmetals Graphite, carbon nanotubes

Layered Al + Al2O3, Cu + C

PCM

2. Base fluids include:

Water

Ethylene- or tri-ethylene-glycols

Oil and other lubricants

Bio-fluids

Polymer solutions

Other common fluids 6


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WHY USE NANOPARTICLES???

Nanoparticles

Better

dispersion

behavior

Less clogging

and abrasion

Much largersurface area-to

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Nano fluid can be produced by two techniques: two-steptechnique and the single-step technique.

Two-step technique: The two step method starts with

producing nanoparticle by one of the physical or chemicalprocesses (e.g., evaporation and inert-gas condensation

processing), and proceeds to disperse them into a base

fluid; most of the nanofluids are produced by two step

method.

Single-step technique: The single step simultaneously

makes and disperses the nanoparticles directly into a base

fluid; best for metallic nanofluids.8


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Liquid molecules close to a solid surface

are known to form layered structures.

With these solid like liquid layers, the

nanofluid structure consists of solid

nanoparticles, solid-like liquid layer, and a

bulk liquid.

The solid-like nano layer acts as a thermal

bridge between a solid nanoparticle and a

bulk liquid and so is key to enhancing thermal

conductivity.

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TRANSIENTHOTWIREMETHOD

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Transient hot-wire apparatus.Transient hot-wire setup.

Hot-wire transition Time 2-8 sec

No convection

Heat applied suddenly

Platinum wire(1.06*10-7m)

k={q/[4(T2

-T1

)]}*ln (t2

/t1

) where k- thermal

conductivity ,T-temperature ,t -time

S.K.Das et al [1]


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SCIENTIFICANALYSISOF AL2O3NANOFLUIDS

Before suggesting a theoretical model for thermal conductivity lets firstlook at the parameters that affect the thermal conductivity of nanofluids from

experiments. According to the report of Argonne National Laboratory, eight parameters

affect the thermal conductivity of nanofluids, they got these results fromabout 124 researchers experiments. These effects are:

1. Particle Volume concentration2. Particle Material

3. Particle Size

4. Particle shape

5. Base fluid material

6. Temperature7. Additive

8. Acidity

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From the experimental results the

general trend is clear thermalconductivity enhancement with

increase in particle volume

concentration(Al2O3 in water)

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EFFECT OF PARTICLE VOLUME CONCENTRATION:

Veeranna and Lakshmi[2]


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The results show increased

thermal conductivity enhancement

for poorer (lower thermalconductivity) heat transfer fluid.

The results show the least

enhancement for water, which is

the best heat transfer fluid with the

highest thermal conductivity of thefluids compared.

EFFECT ON BASE FLUID:



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Experiments show increased

thermal conductivityenhancement with increased

temperature.

(Al2O3 in water)

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EFFECT OF TEMPERATURE:



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Investigator Particles Size (nm) Fluids ObservationsEastman et al

(1997)

Al2O3/CuO/Cu 33/36/ water,oil 60% improvement for 5vol%

CuO particles in water.Lee et al (1999) Al2O3/CuO 24.4,38.4/18.6,23.

6water,EG 20% Improvement for 4 vol%

Cuo/EG mixture.Das et al (2003) Al2O3/CuO 38.4/28.6 water 2-4 fold increase over

range of21oC to 52oC.

Hong et al

(2005)

Fe 10 EG 18% increase for 0.55vol% Fe/EGnanofluids.

Li and Peterson(2006)

Al2O3/CuO

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water

Enhancement withvolume fractionand temperature

Liu et al (2005) CNTs 20-30 m EG,EO 12.4% for EG at 1 vol%,30% for

EO at 2 vol%.

Experimental Studies on Thermal Conductivity of

Nanofluids

Xiang-Qi Wang and Arun S. Mujumdar[4]


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Industrial cooling applications

Electronic cooling

Defense and space

Bio medical applications

Transformer cooling

Nuclear reactor cooling

Heat exchanger

Radiator16


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ADVANTAGES:

Improved Heat Transfer and Stability

Reduced Pumping Power

Minimal CloggingMiniaturized Systems

Cost and Energy Savings

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DISADVANTAGES:

1. Processing cost

2. Use of surfactants for stability which results in lowering

of conductivity due to the formation of a thermal

boundary layer around the particles

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Based on literatures, it has been found that the improvedthermal conductivities of nanofluids are the one of thedriving factors for improved performance in differentapplications. It was found that thermal conductivity of

nanofluids with MWCNT can be increased up to150%[5].

It has been observed that nanofluids can be considered asa potential candidate for many applications.

Nanofluids stability and its production cost are major

factors that hinder the commercialization of nanofluids.By solving these challenges, it is expected thatnanofluids can make substantial impact as coolant in heatexchanging devices.


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REFERENCES

1] S. K. Das, S. U. S. Choi, W. Yu, and T. Pradeep, NanofluidsScience and Technology, John Wiley & Sons, Hoboken, NJ,USA, 2008.

2] Veeranna Sridhara and Lakshmi Narayan Satapathy Al2O3-based nanofluids: a review, Journal of Nanoparticle Research,

vol. 29, no.5, pp.432460, 2008.3] J. Koo and C. Kleinstreuer, A new thermal conductivity

model for nanofluids,Journal of Nanoparticle Research, vol.6,no.6, pp.577588, 2004.

[4] Xiang-Qi Wang, Arun S. Mujumdar, Heat transfercharacteristics of nanofluids: a review, International Journalof thermal science, vol. 46, no.1, pp.1-19, 2007

5] Y. Xuan and Q. Li, Heat transfer enhancement ofnanofluids, International Journal of Heat and Fluid Flow, vol.21, no. 1, pp. 5864, 2000.

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