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CNT

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Mostafa Sobhy

on 29 October 2015

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Transcript of CNT

Carbon Nanotubes (CNT)
What we are going to talk About ?
Introduction to Carbon Nanotube


Experiment showing the effect of CNT


Conclusion
The Experiment
Influence of carbon nanotubes on deionized water pool boiling performances

University Grenoble France

Researchers
Rémi Bertossi - Nadia Caney - Jean Antoine Gruss

Article History
Received 2 September 2014
Received in revised form 30 October 2014
Accepted 31 October 2014
Available online 7 November 2014
Experiment Interpretation
Three parameters can Influence Results
the size of the bubbles
the bubble emission frequency
the number of nucleation sites



For a CNT coated surface
bubbles are observed to be smaller
emission frequency seems to be improved
the number of sites appears to be enhanced.
CNT length influence
For a given heat flux

Superheat is reduced
when the
length of CNT augments

Temperature reduction can reach around 40%
for
10 mim
CNT length

This phenomenon reveals a
better thermal stability
when heat flux augments.
CNT length influence
Heat transfer coefficient
increases with the
CNT length
.

A
specific and interesting result
consists in the evolution of the variation of heat transfer as a function of CNT length

This evolution is quite
linear
between
0 and 5
lm but the c
urve does not increase so greatly

between 5 and 10 mim

A
limitation
of performance depending on
CNT lengths should exist.
Introduction
CNT growth techniques on surfaces
can be very different and depend on materials and geometries of desired nanotubes. These techniques are
very specific
and
complex
, s
o they are achieved by specialized laboratories

A major interest of CNT and NW during boiling is their a
bility to increase the critical heat flux (CHF) accordingly to their height
Literature Survey
M.C. Lu

(2011) and R. Chen (2009)
have measured
very high increase of CHF
concerning
water boiling on silicon NW

It has been shown that
CHF can be multiplied by a factor two
compared to tests led on a plane sample.

Explained by

The
increase of the capillarity
in the NW forest, which permits a vaporization of a higher amount of liquid
Create
numerous micro-cavities
which are potential nucleation sites.
Fullerene Family
What is Carbon and what its forms ?
Carbon is one of the most important elements in our planet. Pure carbon is known to us as
diamond
, if arranged one way in
three dimensions
; and
graphite
if
arranged in another
.

In
diamond
, all the carbon atoms have strong chemical bonds to
four other carbon atoms are arranged tetrahedrally
A diamond is
hard
,
clear
, and
shiny
and is formed under
very high temperatures and pressure
In
Graphite
All the carbon atoms have strong chemical bonds to
three other carbon atoms
, making
sheets,

weak forces
hold the sheets together in stacks that can slide past each other easily
Graphite is
black
, with a
slippery
,
greasy
feel and is formed on
heating coke or coal
Literature Survey
This
interpretation is also shared by Z. Yao, Y.W. Lu
(
2011
)

The authors have studied
copper and silicon NW height effects on water
pool boiling on silicon surfaces

SEM pictures have shown that the
larger the NW are, the more the micro cavities are created

These results are totally in agreement with Chen (2009) results
Carbon Nanotubes
Carbon nanotubes are composed of
carbon atoms
linked in
hexagonal
shapes

Imagine a
sheet of carbon atoms
, which would look like a sheet of
hexagons
. If you
roll that sheet into a tube
, you'd have a carbon
nanotube

Carbon nanotube properties depend on how you roll the sheet

In other words, even though all carbon nanotubes are made of carbon, they can be
very different from one another
based on
how you align the individual atoms
Carbon Nanotubes can be categorized by their structures

Single-wall Nanotubes (
SWNT
)
Single Tube rolled from graphene sheet


Multi-wall Nanotubes (
MWNT
)
Multi
concentric tubes
of SWNT graphene sheets
Carbon Nanotubes
Literature Survey
Boiling performances of CNT have been studied by
J.P. McHale, S.V. Garimella
(
2011
) Observed that
CNT are hydrophobic
,
contrary to copper or silicon

NW
. McHale studied these structures using
deionized water

different surfaces have been tested: a
bare copper sample
, a
40 lm-long CNT copper coated surface


For deionized water,
CNT allows a superheat decrease for a given heat flux
compared to the
bare surface
Heat transfer coefficients as well as
CHF
are greatly improved

Reasons
Trapping of gas or vapor
enhancement of capillarity
increase of total heat exchange surface area
Carbon Nanotubes
Carbon Nanotubes can be categorized by their wrapping Methods

Armchair

Zigzag

Chiral
Literature Survey
Literature Survey (Conclusion)
The previous results are quite
difficult to compare
because of the
numerous variations of test conditions
(
geometr
y,
working fluid
,
nanotubes material and height
. . .).

However, results tend to show that
CNT allows a superheat decrease
at nucleation incipience

Heat transfer coefficient and critical heat flux
Performances are
improved

Surface
Coverage by CNT
and
CNT height
is important

Most of authors explain performances enhancement by
capillary phenomena
and
creation of numerous nucleation sites
thanks to the wetted CNT gathering.

The Expermient Process

The sample is a
stainless steel surface




CNT growth process has been developed in order
to coat both sides of the samples




CNT thicknesses on the two sides of the sample are
3.5 mim, 5 mim and 10 mim high
tube d
iameter is 5 nm
Experimental Apparatus
The tested surface is made of
stainless steel

Faces of 100 mm × 5 mm are brazed on two pins

An
electrical generator
supplies electrical
power to heat the surface

Water f
ar
from the
test sample
is
maintained in the tank at a temperature of 85 C
by a
circulating thermostat

The fluid flows at a
very very low flow rate

to avoid forced convection influence
.
Contact angle
measurements show that surfaces previously
hydrophobic become less hydrophobic or even hydrophilic
after boiling experiments.


CHF is Impoved to nearly 50%
from the bare sample


For a given heat flux, this
reduction in Temperature Difference
can be as high as
40% for 10 lm long
nanotubes


Augmentation of the
number of active nucleation sites
and a
reduction of the bubbles size
Conclusion
References
[1] H.S. Ahn, N. Sinha, M. Zhang, D. Banerjee, S.K. Fang, R.H. Baughman, Pool boiling experiments on multiwalled carbon nanotube (MWCNT) forests, J. Heat Transfer 128 (2011) 1335–1342.
[2] Z. Yao, Y.W. Lu, S.G. Kandlikar, Effects of nanowires height on pool boiling performance of water on silicon chips, Int. J. Therm. Sci. 50 (2011) 2084–2090.
[3] S. Ujereh, T. Fisher, I. Mudawar, Effects of carbon nanotube arrays on nucleate pool boiling, Int. J. Heat Mass Transfer 50 (2007) 4023–4038.
[4] M.C. Lu, R. Chen, V. Srinivasan, V.P. Carey, A. Majumdar, Critical heat flux on pool boiling on Si nanowire array-coated surfaces, Int. J. Heat Mass Transfer 54 (2011) 5359–5367.
[5] R. Chen et al., Nanowires for enhanced boiling heat transfer, Nano Lett. 9 (2009) 548–553.
[6] J.P. McHale, S.V. Garimella, T.S. Fisher, G.A. Powell, Pool boiling performance comparison of smooth end sintered surfaces with and without carbon nanotubes, Nanoscale Microscale Thermophys. Eng. 15 (3) (2011) 133–150.
[7] Y. Im, C. Dietz, S.S. Lee, Y. Joshi, Flower-like CuO nanostructures for enhanced surfaces, Nanoscale Microscale Thermophys. Eng. 16 (3) (2012) 145–153.
[8] H. Hwang, J. Yoon, T. Yeo, H.H. Son, U. Jeong, G. Jeun, W. Choi, S.J. Kim, Enhanced critical heat flux with single-walled carbon nanotubes bonded on metal surfaces, Exp. Therm. Fluid Sci. 60 (2015) 138–147, http://dx.doi.org/ 10.1016/j.expthermflusci.2014.08.015.

[9] J. Dijon, P.D. Szkutnik, A. Fournier, T. Goislard de Monsabert, H. Okuno, E. Quesnel, V. Muffato, E. De Vito, N. Bendiab, A. Bogner, N. Bernier, How to switch from a tip to base growth mechanism in carbon nanotube growth by catalytic chemical vapor deposition, Carbon 48 (2010) 3953–3963.
[10] J. Dijon, A. Fournier, P.D. Szkutnik, H. Okuno, C. Jayet, M. Fayolle, Carbon nanotubes for interconnects in future integrated circuits: the challenge of the density, Diamond Relat. Mater. 19 (5–6) (2010) 382–388.
[11] H.T. Phan, N. Caney, P. Marty, S. Colasson, J. Gavillet, Surface wettability control by nanocoating; the effects on pool boiling heat transfer and nucleation mechanism, Int. Heat Mass Transfer 52 (23–24) (2009) 5459–5471.
[12] Y. Nam, Y.S. Ju, Bubble nucleation on hydrophobic islands provides evidence to anomalously high contact angle of nanobubbles, Appl. Phys. Lett. 93 (2008) 103115.
[13] H.T. Phan, N. Caney, P. Marty, S. Colasson, J. Gavillet, Flow boiling of water on
nanocoated surfaces in a microchannel, J. Heat Transfer 134 (2) (2012).

Fullerenes are a form of
carbon
molecule
that is neither graphite nor diamond
. They consist of a
spherical, ellipsoid, or cylindrical
arrangement of dozens of carbon atoms.

Fullerene
molecules consist of
60, 70, or more carbon atoms
, unlike diamond and graphite, the more familiar forms of carbon.

Spherical
fullerenes are also called
buckyballs
A spherical fullerene looks like a
soccer ball

Cylindrical
ones are called
carbon nanotubes
or buckytubes

The
strongest
,
lightest
and most
conductive
material known

20X
the
strength
of steel

5X
the
elasticity
of steel

1/2
the
density
of aluminum

15X
the
thermal conductivity
of copper

1,000X
the
current capacity
of copper

CNTs
have almost
none of
environmental degradation issues common to
metals—thermal expansion and contraction
,
corrosion
Properties of Fullerene
Allotropes of
carbon
with a
cylindrical nanostructure

Nanotubes are members of the
fullerene
structural family

They are hollow structure with the walls formed by
one-atom-thick sheets
of carbon

CNTs typically have diameters ranging from
1 nm up to 50nm
. lengths are
several microns
Carbon Nanotubes
A very recent study by
G.H. Seo, H. Hwang, J. Yoon(2014)

shows, as previous mentioned by the authors, that bonding a film of SWCNTs to metal surfaces
increases critical heat flux (by an average of 51% compared to bare surfaces
).


Reason
The authors also explain the increase of critical heat flux thanks to increased capillary forces due to a better porosity
Experimental Measurements
Surface temperature Ts
can be estimated from measurements of the electrical resistance by using an
electrical resistance/temperature calibration curve

Working
fluid
is heated
up to 100
C for one hour to be
completely degassed
.

Heat flux
dissipated by
Joule effect is imposed

Boiling curve
and
heat transfer coefficient
can be easily determined

The local boiling heat transfer coefficient is defined as
Wettability of CNT
Static contact angles of the CNT coated surface
s have been measured for different lengths of CNT.
The
uncoated surface
contact angle
is 85
CNT Contact angle
Higher than 90
Heat transfer intensification by CNT
CNT coated
surface performs
better
than the
uncoated
one






For a
given heat flux
, boiling occurs at a
lower superheat
.
Experimental Measurements
For a
given heat flux
, on coated surface,
heat transfer coefficient
enhancement can reach
100%
compared to bare surface



Let us notice that experimental
uncertainties are about 15%.
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