thermal phenomena in nano-fluids

8/10/2019 Thermal Phenomena in Nano-Fluids

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THERMAL PHENOMENA IN NANOFLUIDS

Presented by

RAJESH CHOUDHARY

(Enrollment No.12923039)

Under the Supervision of

Dr. SUDHAKAR SUBUDHI

Department of Mechanical and Industrial Engineering

IIT Roorkee


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Contents

o Introductiono Nanofluids

o Applications

o Synthesis of Nanofluids

o Rheological Properties of Nanofluids

o Mechanisms of heat transfer in Nanofluids

o Forced Convection System

o Natural Convection System

o Conclusion

o Reference

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Introduction

o Nanofluids ?o Need of high heat flow processes

o Interest in improving the efficiency of existing heat transfer processes

o Increased heat transfer can be achieved by:

(i) Increasing T

(ii) Increasing A

(iii) Increasing h

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Nanofluids

o First prepared by Choi SUS in the year 1995 at the Argonne NationalLaboratory

o High surface areas

o Better suspension stability

o Reduced particle clogging

o Pumping power

o Adjustable properties like thermal conductivity

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Applications of Nanofluid

o Transportation (Engine cooling/vehicle thermal management)o Electronics cooling

o Solar water heating

o Diesel combustion

o Nuclear systems cooling

o Heat exchanger

o Other applications (heat pipes, fuel cell, Defence, Chillers, domestic

refrigerator, Space, Drilling, Lubrications, Thermal storage etc.)

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Synthesis of Nanoparticles and Nanofluids

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Nanoparticles

o Physical methods (Grinding methods, Inert Gas Condensation)

o Chemical methods (Chemical Vapour Deposition, Chemical precipitation,

Micro-emulsions, spray pyrolysis, thermal spraying etc.)

Nanofluidso The one-step method

o The two-step method

Figure 1: Two-step method

Ultrasonic

Nanoparticle

Base Fluid

Direct Mix Dispersant

Nanofluid


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Rheological Properties of Nanofluids

Rheological properties of Nanofluids are very important to understandthe heat transfer enhancement:

Thermal Conductivity

Viscosity

Density

Specific Heat

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Rheological Properties of Nanofluids Cont

Thermal Conductivity of Nanofluido Thermal conductivity enhancement ratio

o Metal particles or metal oxide particles

o Particle size

o Particle volume concentration.

o Metal oxide particle volume concentrations below w= 45%

produces an enhancement level up to about 30% is typical and metal

particles with less than w < 1.5% gives an enhancement in thermal

conductivity up to 40%.

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Viscosity of Nanofluido Pressure drop and pumping power

o A maximum increase in viscosity of Al2O3/water nanofluids

was 2.36 times that of water at 5% volume concentration as

observed by Chandrasekar et al. [17]

o Nguyen et al. found that, in general, nanofluid dynamic viscosityincreases considerably with particle volume concentration but

decreases with a temperature increase.

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Density of Nanofluido Density of nanofluid is proportional to the volume ratio of

solid (nanoparticles) and liquid (base fluid) in the system

o Density of solids is higher than that of the liquids

o In the absence of experimental data, the density of the nanofluids

has been reported to be consistent with the mixing theory [19]given by

= 1 + (1)

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Density of Nanofluido Sommers and Yerkes [19]

measured the density of the

Al2O3/propanol nanofluid at

room temperature using two

methods and compared them.

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Figure 2: Comparison of measured and calculated densities of nanofluid [19].


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Specific Heat of Nanofluido Smaller than that of the base fluid

o The first model is one which is analogous to the mixing theory

and the specific heat of a nanofluid is expressed as

, = 1 , + , (2)

o The second model is based on thermal equilibrium mechanism

and the specific heat of a nanofluid is expressed as

, = 1 ,+ , (3)

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Mechanisms of Enhancement of Heat Transfer

o Enhancement in thermal conductivity is the leading effecto At room temperature, metals in solid phase have higher thermal

conductivities than those of fluids

o For example, the thermal conductivity of copper at room temperature is

about 700 times greater than that of water and about 3000 times greater

than that of engine oilo Moreover, the effective thermal conductivity depends on several

mechanisms of particle motion.

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Mechanisms of Enhancement of Heat Transfer Cont

Dispersion of the suspended particleso Surface-active substances (surfactants) can increase the kinetic stability

of emulsions

o Some of the surfactants are thiols, oleic acid, laurate salts, etc.

Intensification of turbulence

o Thermal conductivity (kth)

o Effective thermal conductivity (kth+kturb) in turbulent flow due to the

effects of turbulent eddies

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Brownian motiono Random movement of particles suspended in a liquid or gas

o Brownian motion intensifies with an increase in temperature as per the

kinetic theory of particles.

o Keblinski et al. [14] have suggested that the potential mechanism for

enhancement of thermal conductivity is the transfer of energy due to thecollision of higher temperature particles with lower ones.

o Effect of bulk viscosity.

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Thermophoresiso Thermophoresis or the Soret effect

o Particles travel in the direction of decreasing temperature

o Heat transfer increases with a decrease in the bulk density

o Most significant in a natural convection process

Diffusiophoresis

o Osmo-phoresis

o Migration of particles due to concentration gradient

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Force Convection in Nanofluids

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Figure 3: Convective heat transfer under constant wall-temperature condition [20].


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Force Convection in Nanofluids Cont

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Figure 4: Experimental values of heat transfer coefficient and calculated values from Seider

Tate equation for Al2O3/water nanofluid versus Peclet number at different volume concentration

[20].


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Natural Convection in Nanofluids

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Figure 5: Convective heat transfer in fully developed laminar flow

under constant heat flux[22].


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Natural Convection in Nanofluids Cont

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Figure 6: Nusselt and Rayleigh numbers as a function of time (heat flux of 190 W/m2).

(a) Nusselt number and (b) Rayleigh number [22].


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Conclusion

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o Addition of nanoparticles to a liquid increases the viscositysignificantly and the thermal conductivity moderately, however the

specific heat and density changes modestly.

o Prandtl number of nanofluids increases as particle volume

concentration increases but decreases with an increase in the

temperature.o Reynolds number of nanofluid for a specified geometry and velocity

increases with temperature and decreases with an increase in particle

volumetric concentration.

o The convective heat transfer coefficient of nanofluids in-creases with

an increase in temperature and concentration and is significantly higher

than that of the base fluid.

o In general, nanofluids show many excellent properties promising for

engineering application. But there are still several important issues that

need to be solved for applications of nanofluids in engineering.


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References

1. R. Saidur, K.Y. Leong, H.A. Mohammad, A review on applications and challenges of

nanofluids,Renewable and Sustainable Energy Reviews, 15 (2011), 164616682. Kostic.www.kostic.niu.edu/DRnanofluids.

3. Yanjiao Li, jingen Zhou, Simon Tung, Eric Schneider, Shengqi Xi, A review on

development of nanofluid preparation and characterization, Powder Technology, 196

(2009), 89-101

4. Lazarus Godson, B. Raja, D. Mohan Lal, S. Wongwises,Enhancementof heat transfer using

nanofluidsAn overview, Renewable and Sustainable Energy Reviews, 14 (2010), 629641

5. Choi SUS, Enhancing thermal conductivity of fluids with nanoparticles, in Developments

and Applications of Non-Newtonian Flows,ASME FED 231/ MD, 66 (1995), 99103

6. Yu Wei and Xie Huaqing, AReview on Nanofluids: Preparation, Stability Mechanisms, and

Applications,Journal of Nanomaterials (2012)

7. J. A. Eastman, S. U. S. Choi, S. Li, W. Yu, and L. J. Thompson, Anomalously increasedeffective thermal conductivities of ethylene glycol-based nanofluids containing copper

nanoparticles,Applied Physics Letters, 78 (2001), 718720

8. H. T. Zhu, Y. S. Lin, and Y. S. Yin, Anovel one-step chemical method for preparation of

copper nanofluids,Journal of Colloid and Interface Science, 277 (2004), 100103

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References

9. X. Feng, H. Ma, S. Huang, Aqueous-organic phase-transfer of highly stable gold, silver, and

platinum nanoparticles and new route for fabrication of gold nanofilms at the oil/water

interface and on solid supports, Journal of Physical Chemistry B, 110 (2006), 1231112317

10. W. Yu, H. Xie, L. Chen, and Y. Li, Enhancement of thermal conductivity of kerosene-based

Fe3O4nanofluids prepared via phase-transfer method, Colloids and Surfaces A, 355 (2010),

109113

11. Grimm A. Powdered aluminium-containing heat transfer fluids, German Patent DE 4131516

A1 (1993).

12. Pak B C, Cho I Y, Hydrodynamic and heat transfer study of dispersed fluids with sub-micron

metallic oxide particles, Experimental Heat Transfer, 11 (1998), 15170

13. Xuan Y, Li Q, Heat transfer enhancement of nanofluids, International Journal of Heat and

Fluid Flow, 21 (2000), 5864

14. Keblinski P, Phillpot S R, Choi SUS, Eastman J A, Mechanisms of heat flow in suspensions

of nanosized particles (nanofluids), International Journal of Heat and Mass Transfer, 45

(2002), 85563

15. Buongiorno J, Convective transport in nanofluids, Journal of Heat Transfer ASME, 128

(2006), 240-250

16. Vajjha RS, Das DK. ,Experimental determination of thermal conductivity of three

nanofluids and development of new correlations, International Journal of Heat and Mass

Transfer, 52 (2009), 467582

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References

17. Chandrasekar M, Suresh S, Chandra Bose A. Experimental investigations and theoretical

determination of thermal conductivity and viscosity of Al2O3/water nanofluid,

Experimental Thermal and Fluid Science, 34 (2010), 21021618. Nguyen CT, Desgranges F, Galanis N, Roy G, Mare T, Boucher S, et al. Viscosity

data for Al2O3/water nanofluid-hysteresis: Is heat transfer enhancement using nanofluids

reliable? International Journal of Thermal Sciences, 47 ( 2008), 10311

19. Sommers AD, Yerkes KL. Experimental investigation into the convective heat transfer

and system-level effects of Al2O3-propanol nanofluids, Journal of Nanoparticle Research,

12 (2010), 10031420. Heris SZ, Esfahany MN, Etemad SGh, Experimental investigation of convective heat transfer

of Al2O3/water nanofluid in circular tube, International Journal of Heat Fluid Flow, 28 (2007),

203-210

21. Hwang KS, Jang SP, Choi US, Flow and convective heat transfer characteristics of water-

based Al2O3nanofluids in fully developed laminar flow regime, International Journal of Heat

Fluid Mass Transfer, 52 (2009), 193-19922. Wen D, Ding Y, Formulation of nanofluids for natural convective heat transfer applications,

International Journal of Heat Fluid Mass Transfer, 26 (2005), 855-864

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thermal phenomena in nano-fluids

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