It's a presentation prepared from a paper named "Latest developments on the viscosity of nanofluids." The original paper is an open-source content in ELSEVIER.

1. “LATEST DEVELOPMENTS ON THE
VISCOSITY OF NANO-FLUIDS”
Md. Mydul Islam
# 0417102028
Mechanical Engineering
BUET
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2. ABOUT THIS PAPER
 Published in ELSEVIER
(Accepted: 7 October 2011)
 Authors:
I.M. Mahbubul, R. Saidur, M.A. Amalina
(Department of Mechanical Engineering, University of Malaya,
Malaysia)
 Keywords:
Nanofluid, Viscosity, Temperature, Particle size, Volume
concentration
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3. WHAT IS NANO-FLUID
 Nanofluid is a solid–liquid mixture which consists of
nanoparticles and a base liquid.
 Nanoparticles:
- Metal (Cu, Ni, Al, etc.)
- Metal oxides (Al2O3, TiO2, CuO, SiO2, Fe2O3, Fe3O4,
BaTiO3, etc.)
- Some other compounds (AlN, SiC, CaCO3, graphene, etc.)
and
 Base fluids:
Water, EG (Ethylene Glycol, PG (Propylene Glycol), Engine
oil, etc.
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4. IMPORTANCE OF NANO-FLUID
 Nanofluid draws researcher's attention because of its potential
application in heat transfer.
 Due to very small sizes and large specific surface areas of
the nanoparticles, nanofluids have superior properties like
high thermal conductivity, minimal clogging in flow passages,
long-term stability, and homogeneity.
 Better than conventional fluids.
 Works by Choi was the pioneer in the research area of
nanofluids.
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5. RELATED WORKS
 Mainly focused on Thermal Conductivity.
 Related other properties:
- Heat Transfer enhancement
- Thermal Conductivity enhancement
- Thermal Transport
- Electrical Conductivity
- Thermal Diffusion
- Cooling property etc.
 Very few works on Viscosity.
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6. VISCOSITY AND RELATED FACTORS
 Viscosity:
- Internal resistance of a fluid to flow
- Important property for all thermal applications involving fluids
- Pumping power is related with the viscosity
 Main Factors:
- Temperature
- Particle Size
- Volume concentration of nanoparticles
 Most of the works gave priority to the Volume Concentration.
(Table: 1)
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7. 7

8. NANO-FLUID PREPARATION
 Important for both Experimental and Application purpose.
 2 ways of preparation:
(i) Single Step Method
- Increased stability
- Minimal agglomeration
- Limited to low pressure fluids
(ii) Two Step Method
- Mostly preferred
- Suitable for oxide nanoparticles
- Partial dispersion, Quick agglomeration risk
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9. EXPERIMENTAL STUDIES
Effect of Temperature
 Most of the experiments are done within the temperature
range of 5~10 to 50~60 degree Celsius.
 There are some contradictory results.
 Viscosity decreased with Temperature rise:
- Yang et al.
- Nguyen et al.
- Anoop et al.
- Duangthongsuk and Wongwises
- Turgut et al.
- Kole and Dey
- Pastoriza-Gallego et al.
- Lee et al.
- Namburu et al.
- Kulkarni 9

10.  Both Namburu and Kulkarni showed that the
inverse relation between viscosity and temperature
are Exponential in nature.
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11.  Contradiction:
- Chen et al. works on the range of 5 C to 65 C for
MWCNT/DW and indicated that relative viscosity increases
significantly with temperature after 55 C
- Prasher stated that viscosity is independent of temperature.
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12. Effect of Particle Size
- Few studies on it.
- Contradictory results.
 Nguyen et al. have some good findings:
- very less effect of particle size in case of low volume
concentration.
- at high %volume Viscosity follows the Uptrend manner with
increasing particle size.
 He et al. also found similar result.
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13.  Lu and Fan found different results:
- Viscosity decreases with particle diameter
 Anoop, Chevalier, Namburu, Pastoriza-Gallego also colcluded
to the same findings.
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14.  Prasher et al. Stated:
- Nanofluid viscosity is not an exact function of nanoparticle
diameter
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15. Effect of Volume Fraction
 No significant contradiction.
 All experiments concluded that:
- viscosity increases with higher value of volume fraction.
- at lower concentration, this increase follows almost linear
trend.
- at higher volume fraction, most of the nanofluid suspensions
show shear-thinning property.
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16. THEORETICAL STUDIES
 Einstein is the pioneer to the theoretical formulations on
nanofluid viscosity.
 Einstein’s proposal:
Here,
μnf - viscosity of the nanofluid
μbf - viscosity of the base fluid
ϕ - volume fraction of the particle
 Limitations:
- does not consider structure & particle–particle interaction
- only valid for very low volume fraction
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17.  Modification from Einstein’s equation:
- Batchelor:
- Lundgren :
- Franken and Acrivos :
Here,
ϕm = maximum particle volume fraction (experimentally)
 There are other correlations similar to these ones.
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18.  All of the previous correlations are based on
volume fraction.
 There are few formulations with particle size and
temperature in it.
 Graham used Franken - Acrivos and Einstein
relation to obtain:
Here,
dp - particle radius
h - inter-particle spacing. 18

19.  Correlation with Temperature formulated by White:
Here,
(μo,To) are reference values and (a, b, c) given in the table by
White, are dimensionless curve-fit constants.
 Correlation by Yaws:
Here A, B, C and D are fitting parameters
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20.  There are some more research works that tried to
form a correlation that relates all factors, i.e.
Temperature, Particle Size, Volume Fraction etc.
 Masoud Hosseini et al. developed this formulation
for the viscosity of Al2O3/Water nanofluid:
Φh - hydro dynamic volume fraction
d - particle diameter
r - thickness of the capping layer
To - reference temperature
T - measured temperature
a, b, and c - empirical constants (experimental)
m is a factor
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21. CONCLUSION
 Viscosity of nanofluids varies with different factors.
 Temperature and Nanoparticle Size are the two
contradictory factors. They shows different
outcomes for different conditions.
 Volume fraction augments the viscous effect.
 There is not a single correlation that can work for
all types of nanofluids in all conditions.
 Different formulations are developed and more can
be done later.
 There is a huge scope to work both experimentally
and theoretically on nanofluid properties.
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22. Thank You
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