中國機械工程學刊第二十八卷第二期第123~131頁(民國九十六年)
Journal of the Chinese Society of Mechanical Engineers, Vol.28, No.2, pp.123~131 (2007)
Producing Aluminum-oxide brake nanofluids
using plasma charging system
Mu-Jung Kao *, Ho Chang*, Yuh-Yih Wu *, Tsing-Tshih Tsung*,
Hong-Ming Lin**
Keywords: Aluminum-oxide brake nanofluids
(AOBN), plasma, vapor-lock.
INTRODUCTION
It has been recognized that the heat transport
properties of nanofluids which contain the
suspensions of solids particles in liquids is greater
than that of fluids with no nanoparticles. The
Argonne Research Institute also unveiled the first
nanofluid patent [1] claiming heat conductivity to
be 1.6 times over the yield of water. The use of
Al2O3 particles about 13 nm in diameter at 4.3%
volume
fraction
increased
the
thermal
conductivity of water under stationary conditions
by 30% [2].This showed that nanofluid is a
revolutionary product as a heat transmitter or
lubrication agent. The metal aluminum block can
be vaporized instantly by a self-designed plasma
electric arc at a high temperature. A self-designed
collecting and processing chamber was used to
carry out the experiment and produce nanofluid.
Vaporized gas and particles were then directed
into the collecting pipe by a guiding system and
mixed sufficiently with the pre-cooled DOT3
brake fluids to form the nano-aluminum
suspension in brake fluid. The minimum particle
diameter is about 10nm and average diameter is
about 50nm. The study showed that when the
temperature of the cooling liquid decreased to 3℃
the nanoparticles had a small diameter and even
distribution in brake fluid. The confirmation of
appearance of nano-suspension was determined by
Transmission Electron Microscopy (TEM), a
particles distribution analyzer (LB-500 HORIBA)
and X-RAY. The X-ray diffraction (MAC-MXP18,
wavelength: 1.54nm) was used to show the pattern
of nanoparticles in brake fluid. The average
diameter reached about 50nm and the shape of the
nano Aluminum oxide fluid particle showed
circle geometry and was uniformly dispersed in
the brake fluids thus warranting nanofluids to be a
revolutionary product as a heat transmission or
ABSTRACT
This study examines the characteristics of
Aluminum-oxide brake nanofluids (AOBN)
manufactured by a home-made machine, the
plasma arc system. The plasma electric arc
welding machine was specially modified to be a
nanofluid production system in the experiment.
Argon was chosen to be the plasma gas because it
can be ionized very easily and needs only lower
voltage to keep the production of plasma electric
arcs continuous. The aluminum bulk specimen is
then mixed with DOT3 break fluid. The AOBN
thus obtained shows a higher boiling, higher
viscosity and higher conductivity. Furthermore,
they are affected by the synthesizing parameters
such as cooling liquid temperature and vacuum
pressure. The confirmed appearance of
nanoparticles was determined by Transmission
Electron Microscopy (TEM) and X-RAY. This
study revealed that a home made plasma arc
machine can produce AOBN which surpasses the
boiling point to reduce the occurrence of vaporlock, higher viscosity, higher conductivity and
circle geometry common to the superior
performance of brake nanofluids.
Paper received June, 2005. Revised September, 2005, Accepted October,
2005, Author for Correspondence: Mu Jung Kao
*
Graduate Institute of Mechanical and Electrical
Engineering, National Taipei University of
Technology, Taipei, Taiwan, 106,R.O.C
**
Department of Materials Engineering,
Tatung University, Taipei, 104, R.O.C.
1
J, CSME Vol.28,No.2 (2007)
lubrication agent.
EXPERIMENTAL & THEORY
Experimental
The plasma electric arc welding machine was
designed to be a nano production system.
Operating parameters are shown in table 1. The
cooling liquid is set at 3℃ and 15A current
operated with voltage at 220. The plasma system
was used to vaporize the aluminum in the
processing chamber by high temperature from the
instantly extracted plasma electric arc.
Figure 1 Schematic diagram of plasma nanofluid
system
To control the parameters such as cooling
temperature, plasma gas and nanofluids collecting
chamber pressure reached the specified criteria.
When it falls within the specified criteria the
specimen is regarded as a stabilized nanofluid.
The Redwood universal Viscometer and the
transient hot-wire method were also employed to
measure viscosity and thermal conductivity
(Decagon KD2 measure meter).
Table 1 Parameters for Plasma charging
system processing
Curr
ent
(A)
Volta
ge
(V)
15
220
Cooling
Liquid
Temperat
ure
(℃)
3
Press
ure
(torr)
Processi
ng (min)
760
12
The parameters to vaporize metal into gas in a
short period are as follow: the increase of current
will result in rising temperature of the plasma
electric arc and the diameter of the electric arc is
also increased. The influence will reflect on the
particle diameter of the particle produced. Too
large plasma current density produces overheat of
the plasma injection point. The current of 50A and
temperature of 3℃ is the best experiment
parameter. So to get the distribution of particles
a diameter of about 50~60nm is used. As can be
seen from figure 1, the nanofluid production
system was improved from a plasma electric arc
welding machine. In order to obtain the electric
arc, plasma gas was used. Argon was chosen as
the plasma gas because it can be ionized very
easily and needs only low voltages to keep the
continuous production of plasma electric arcs. A
shield gas is used to protect the electrode, welding
pool and melting metal from pollution or
oxidation. The same type of the plasma gas
(mixture of Ar +H2 and mixture of Ar+He) was
chosen to be the shield gas. This was incorporated
with the self-designed collecting and processing
chamber to carry out the experiment and produce
nanofluid. The nanoparticles after vaporization
were guided into the collecting chamber by
pressure difference.
Theory
Nanoparticles Nucleation
The process of Al2O3 nanoparticle synthesis
that entails embedding pure bulk aluminum in the
cooling liquid (the brake fluid) to create vapor
through arc spraying requires undergoing three
stages. These stages are synthesis, growth and
cooling [4]. The crystal growth process starts
with the nucleation stage. Several atoms or
molecules in a supersaturated vapor or liquid start
forming clusters. The bulk free energy of the
cluster is less than that of the vapor or liquid. The
total free energy of the cluster is increased by the
surface tension energy. However, this is
significant only when the cluster is small. A
cluster of radius smaller than a critical radius,
r*will evaporate (or dissolve in the solution) but a
cluster of radius greater than r* will become stable
and will increase its size by the addition of other
atoms and is thus "growing"! The critical radius r*
defines a critical energy barrier, △GT , that we
need to overcome in order to obtain a stable
nucleus that will keep growing and eventually
become a large single crystal! Thermodynamics
can help us describe the process. Assuming a
spherical shape for the nucleus the free energy
[3,4] of its formation is:
2
△GT = 4π r2 s + (4/3) πr3 △Gv
(1)
where △GT is the total free energy; r is the radius
of cluster; s is the specific surface free energy,
△Gv is the volume free energy; △GT is the free
energy change per unit volume forming the stable
solidification from vapor or liquid. The total free
energy △GT goes through a maximum △GT *at a
critical radius r* which can be obtained
by derivation of total free energy as given above
with respect to radius and solving: (d△GT /dr) =
0 The Plasma arc method is the crystal growth
under vapor - solid equilibrium conditions. The
temperature of the starting material (powder
form) is higher than the nucleation/crystal growth
region. This imposed temperature gradient leads
to a mass flow resulting in a net mass transport of
vapor species towards the nanoparticles growth
site. In the process, a material is transformed from
a gas state to a solid state, △GT is correlated to
the saturation level, while a high level of
saturation is determined by the differential in arc
current discharge temperature and cooling liquid
temperature This means that in order to derive a
higher metal nanoparticle synthesis rate, the metal
would need to evaporate under high temperature
of plasma and coagulate under low temperature in
order to achieve the effect. Plasma arc spray
converts metal rod material into vapor and then is
put through coagulation and mixed with the brake
liquid to form brake nanofluid.
hN b
⎛ E ⎞ + ⎛ MRT
exp ⎜
⎟ 5⎜
Vm
⎝ π
⎝ RT ⎠
A
Aσ
2
-
RESULTS AND DISCUSSION
With the conductivity measure meter, Decago
with KD2, the specimen was measured 20 times,
each lasting 10 sec. The measurement time
should be kept short to avoid convection which
may undermine the measurement accuracy. Table
2, the boiling point of AOBN would increase
approximately 8 oC and the heat conductivity of
AOBN is 1.5 times over the DOT3 brake fluid
thus warranting nanofluid to be a revolutionary
product as a heat transmission or lubrication agent.
Nanofluids with the aluminum oxide provide the
conductivity rising from 0.13 w/moc to 0.19
w/moc.
(2)
1/ 2
⎛ MRT ⎞
5⎜
⎟
π
⎠
η = ⎝
16 N A σ 2
/ 16 N
In which, M being a mass; NA being the
Avogadro’s number; π being a gas viscosity; being a molecule’s radius; what can be deduced
from equation(3) is that rising temperature will
cause gas viscosity to rise. Nanofluid viscosity is
derived from the liquid plus gas model (2) +(3) as
denoted in equation (4). When the liquid‘s
temperature rising, the first part of equation (4)
would steer the liquid viscosity to drop in relation
to the exponential function, and as the temperature
T increases, the second parts of equation. (4)
would drive the nanofluid’s viscosity to rise
alongside the nanoparticle mass and the
multiplication of the constant number R, hence
concluding how the viscosity rating of nanofluids
tends to be higher than most liquids from which it
can be concluded to related to second term.
The Eyring thermal activation theory [5,6] is
used to derive a liquid viscosity expressed by
equation. (2)
hN b
⎛ E ⎞
exp⎜
⎟
Vm
⎝ RT ⎠
1/ 2
--------------- (4)
Nanofluids Viscosity
µ=
⎞
⎟
⎠
Table 2 brake fluid’s boiling point & Conductivity
(3)
DOT3
(brake fluid)
The letter h being a Planck constant; Nb being a
molecule mass; E being the molecular kinetic
energy; Vm being the volume of molecule. What
can be extrapolated from equation (2) is that rising
temperature would trigger the viscosity to appear
in an exponential function (with the denominator
value going up) to cause the µ value to diminish.
The gas viscosity is then put through the gas
movement equation [7] to express by equation. (3),
Dry boiling
240℃
point (min)
Conductivity
0.13 w/m℃
(25℃)
3
DOT3+2%wt Al2O3
248℃
0.19 w/m℃
J, CSME Vol.28,No.2 (2007)
14
beams and only allowing light from electron gun
central beam through.
12
q(%)
10
8
6
4
2
0
10
100
1000
Diameter(nm)
Figure 2 Diameter distribution of aluminum oxide
under 50A
Figure 4 The TEM image of Aluminum Oxide
Figure 2 shows the XRD analysis for second
particle diameter distribution from 20-110nm and
the average diameter is about 50nm.
(0 4 6)
Delta Al2O3
(0 4 0)
200
100
(3 1 1)
(0 2 0)
Intensity
150
50
0
0
10
20
30
40
50
60
70
80
90
Figure 5 The brakefluid’s temperature and
viscosity fluctuations
2 Theta
Figure 3 The XRD pattern of Al2O3
Figure 5 shows the temperature fluctuation
come to affect the viscosity of AOBN and
DOT3 brake fluid. The nanofluids are subjected
to the rising temperature and the nanofluids’
viscosity to drop. The viscosity of nanofluid
consisting of aluminum-oxide nanoparticles
tends to be higher than DOT3 liquid. The
viscosity of nanoparticles is like the kinetic
theory of gases. The theory allows one to
estimate the hard sphere collision of molecules
from the measurement of the gas viscosity.
Equation (3) can be rearranged to obtain an
expression for the gas viscosity in terms of the
collision diameter. The T1/2 dependence is
unusual because gases demonstrate the opposite
type of temperature. That is, nanoparticles
viscosities increase with increasing temperature.
However the nanofluids demonstrate the
By inspecting the XRD results of the Nanoparticles, as shown in figure 3. the XRD analysis
for the crystalline phase of Aluminum Oxide
(Al2O3) can be seen. The crystalline phase was
determined by X-ray Diffraction (XRD, MACMXP18). All peaks obtained by XRD analysis
were assigned by comparison with data from the
Joint Committee on powder Diffraction Standards
(JCPDS). The micro structure of the prepared
nanofluid was determined using a Transmission
Electron Microscope (TEM, JEOL JSM1200EX2). Figure 4 depicts an image of
aluminum oxide particles with diameters from 2050nm. The growth of nucleus shows that the
aluminum oxide cohesion is big than surface
tension which so form as the round geometer. The
bright field image is the substrate area which is
obtained by intentionally excluding all diffracted
4
opposite type of temperature dependence from
liquids, that is, liquid viscosities decrease with
increasing temperature so nanofluids’ viscosity
drops slowly at high temperature. The higher
boiling point of AOBN is contributed by the
aluminum oxide nanoparticles. According to a
rudimentary braking theory of converting
kinetic energy into heat energy, AOBN thus
obtained possesses such characteristics as high
boiling point, high viscosity and a stabilized
state; making it a novel product as a heat
transmission or lubrication agent. In a vehicle
brake system, the heat energy is absorbed
through braking parts and the braking command
dispersion is mainly achieved through the
braking bearing pads, braking drum or friction
between the disks to create the blocking effect.
A vehicle’s kinetic energy is dispersed through
the heat generated during
the braking motion, and the braking command
is thus generated through the presence of the
heat energy, while the heat energy at the bearing
pads arisen from braking is conveyed to the
brake fluid through the braking fluid’s hydraulic
pistons.
However, if the brake fluid’s
temperature surges to the boiling point to create
a boiling phenomenon. It turn forms a vaporlock, this effectively disables the hydraulic
system from conveying the heat, resulting in the
moving hazard of brake failure. The study
reveals that brake nanofluids serve to enhance
the boiling point and higher conductivity which
then reduces the occurrence of vapor-lock, thus
increasing driving safety.
This study was supported by the Depart of
Industrial Technology, Ministry of Economic
Afairs, R.O.C., contract No. 94-EC-17-A-16-S1051-B3）
REFERENCES
Argonne National Laboratory, Kate of Patent,
No.:US
6221275
B1,Date
of
Patent:Apr.24．2001.
Masuda H., Ebata A. et. al. “Alteration of thermal
conductivity and viscosity of liquid by
dispersing ultra-fine particles(dispersions of
γ- Al2O3, SiO2and TiO2 particles),” Netsu
Bussei (Japan) 4, pp.227-233(1993).
William D. Callister., materials science and
Engineering : an Introduction, Wiley,
Seventh Edition, New York, U.S.A,
pp.313-315 (2006)
William F. S., Foundations of materials science
and Engineering, Mcgraw-Hill, third
Edition, U.S.A, pp.120-124 (2004)
5Eyring,H.& Eyring,H. :Significant liquid
structures New York: Wiley, pp.30-55
(1969)
Philip. T E., Mukund. R.P, et. al. J.Appl. Phys.73,
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Keith J L.: The World of Physical Chemistry,
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電漿電弧系統生產奈米氧
化鋁煞車油
CONCLUSION
高木榮 張合 吳浴沂 鐘清枝 +林鴻明
國立台北科技大學機電所
+
大同大學材料所
Aluminum-oxide brake nanofluids can be
prepared by plasma charging system when
applying the cooling temperature and plasma arc
produce rate. There are three good characteristics
in aluminum oxide brake nanofluids deriving from
the home-made plasma charging system. First, the
boiling point of AOBN would increase
approximately 8oc. Second, the viscosity of
AOBN is consistently higher than that of DOT3
(traditional) brake fluid. Finally, AOBN
conductivity is 1.5 times over the yield of DOT3
brake fluid which is from 0.13 w/moc to 0.19
w/moc. The stable and even distribution
nanoparticles provide good performance, thus
warranting nanofluids to be a revolutionary
product as a heat transmission or lubrication agent.
本文旨在探討電漿電弧放電所產生之
奈米氧化鋁煞 車油製程和分析其特
性，對於產出奈米氧化鋁顆粒大小進
行檢測分析，對煞車油共沸點及粘度
具體之探討;其奈米粒徑約為50nm奈
米氧化鋁粒，奈米氧化鋁顆粒外形呈
現圓形提供煞 車系統較低起始摩擦
力，同時提升煞車油共沸點及粘度性
能增加煞車安全性。
ACKNOWLEDGMENT
5