6.3 Ferrofluids 113
In view of the technical applications, besides heat capacity and thermal conductivity, the influence on the rheological properties is of essential importance. Figure
6.3 displays, as an example, the dynamic viscosity η of a nanofluid consisting of
CuO nanoparticles in ethylene glycol as a function of the volume fraction c of
nanoparticles [4]. These results are very important, as they show that, for particle
concentrations higher than 10
−3 (=0.1%), the dynamic viscosity increases exponentially with a power of three, η ∝ c
3
.
Summarizing the content of Figures 6.2 and 6.3 one realizes a very promising
improvement of the coolant liquid, as the dramatic increase of the dynamic viscosity above a volume content of 10
−3 is out of the range, where an interesting increase
of the thermal conductivity is observed. These improved properties allow the
design of smaller highly efficient cooling systems, which may be of great importance in microtechnology. Looking at applications in the automotive industry, the
long-term stability has to be analyzed in great detail. Such long-term applications
could be impeded by a tendency of sedimentation or thermophoresis.
6.3
Ferrofluids
6.3.1
Properties of Ferrofluids
Ferrofluids are a special type of nanofluids. As nanoparticles, superparamagnetic
ceramic particles are applied. (For “superparamagnetism”, please see Chapter 8.)
The importance of ferrofluids is based on their broad range of applications in
Figure 6.3 Dynamic viscosity of an ethylene
glycol / CuO nanofluid as a function of the
volume content of nanoparticles plotted in a
double-logarithmic system [4]. Up to a
particle volume fraction of 10
−3 , the viscosity
is not influenced by the additions of
nanoparticles. At higher concentrations, the
dynamic viscosity increases exponentially, to
the power of three, η ∝ c
3 .
10
–6
10
–5
10
–4
10
–3
10
–2
10
–1
particle volume fraction c
10
–2
10
–1
10
0
10
1
10
2
10
3
dynamic
viscosity
η [Pa
s]
experimental data
range of constant viscosity
viscosity increases exponentially
3
c
η ∝
In view of the technical applications, besides heat capacity and thermal conductivity, the influence on the rheological properties is of essential importance. Figure
6.3 displays, as an example, the dynamic viscosity η of a nanofluid consisting of
CuO nanoparticles in ethylene glycol as a function of the volume fraction c of
nanoparticles [4]. These results are very important, as they show that, for particle
concentrations higher than 10
−3 (=0.1%), the dynamic viscosity increases exponentially with a power of three, η ∝ c
3
.
Summarizing the content of Figures 6.2 and 6.3 one realizes a very promising
improvement of the coolant liquid, as the dramatic increase of the dynamic viscosity above a volume content of 10
−3 is out of the range, where an interesting increase
of the thermal conductivity is observed. These improved properties allow the
design of smaller highly efficient cooling systems, which may be of great importance in microtechnology. Looking at applications in the automotive industry, the
long-term stability has to be analyzed in great detail. Such long-term applications
could be impeded by a tendency of sedimentation or thermophoresis.
6.3
Ferrofluids
6.3.1
Properties of Ferrofluids
Ferrofluids are a special type of nanofluids. As nanoparticles, superparamagnetic
ceramic particles are applied. (For “superparamagnetism”, please see Chapter 8.)
The importance of ferrofluids is based on their broad range of applications in
Figure 6.3 Dynamic viscosity of an ethylene
glycol / CuO nanofluid as a function of the
volume content of nanoparticles plotted in a
double-logarithmic system [4]. Up to a
particle volume fraction of 10
−3 , the viscosity
is not influenced by the additions of
nanoparticles. At higher concentrations, the
dynamic viscosity increases exponentially, to
the power of three, η ∝ c
3 .
10
–6
10
–5
10
–4
10
–3
10
–2
10
–1
particle volume fraction c
10
–2
10
–1
10
0
10
1
10
2
10
3
dynamic
viscosity
η [Pa
s]
experimental data
range of constant viscosity
viscosity increases exponentially
3
c
η ∝