Synthesis and Characterization of Nanofluids …
23
have found that it is not only affected by the properties of the components of the
nanofluid but also their interaction with each other (Ganguly et al. 2009; Minea
and Luciu 2012; Shen et al. 2012). Chakraborty and Padhy (2008) found that the
agglomeration of the nanoparticles leads to efficient electrical conductivity due to
the nanoparticles making physical contact with each other. But in contrast to that, they
have stated that the agglomeration of the nanoparticles also leads to larger particle
size having larger mass that may reduce the electrophoretic mobility due to increased
viscosity of the nanofluid.
The DLVO theory developed for explaining the stability of colloids in suspension
states that there is a formation of a charged layer on a colloidal particle in the
nanofluid. This layer is composed of ions that are charged opposite to the particle
surface and so form a charged diffuse layer over the particles. These ionic charges
are found to be forming due to the adsorption and desorption of ions present in the
solution on the particle surface (Cruz et al. 2005). These charged particles can then
transfer the charge and behave as charge carriers. In a nanofluid, the nanoparticles
act as carriers of electrical charge. The electrical double layer (EDL) has also found
to be one of the mechanisms responsible for the electrical transport properties of the
nanofluids by many researchers (Chakraborty and Padhy 2008; Ganguly et al. 2009;
Minea and Luciu 2012).
4.1 Measurement of Electrical Conductivity of the Nanofluids
Electrical conductivity of nanofluids has mostly been measured by researchers all
around the world by using electrical conductivity metre consisting of a probe, whose
electrical circuit with the circular electrode that makes up the working principle of the
electrical conductivity metre is shown in Fig. 9a. The one shown in Fig. 9b is a typical
electrical conductivity measuring device known as a four-cell conductivity electrode
metre (CyberScan CON 11) made by Eutech Instruments Pte Ltd in Singapore having
in-built automatic temperature compensation (ATC). This metre gives instant value
of electrical conductivity and temperature.
4.2 Factors Affecting the Electrical Conductivity
of the Nanofluids
Electrical conductivity being the property dependent on the components of the
nanofluid can be affected by many factors. As discussed earlier, the electrical conductivity of the nanofluids is dependent on the charge over the particles. They can also be
dependent on the amount and size of these charge carriers, that is, the nanoparticles.
These charges on the nanoparticles are dependent on the pH (Sigmund et al. 2000).
23
have found that it is not only affected by the properties of the components of the
nanofluid but also their interaction with each other (Ganguly et al. 2009; Minea
and Luciu 2012; Shen et al. 2012). Chakraborty and Padhy (2008) found that the
agglomeration of the nanoparticles leads to efficient electrical conductivity due to
the nanoparticles making physical contact with each other. But in contrast to that, they
have stated that the agglomeration of the nanoparticles also leads to larger particle
size having larger mass that may reduce the electrophoretic mobility due to increased
viscosity of the nanofluid.
The DLVO theory developed for explaining the stability of colloids in suspension
states that there is a formation of a charged layer on a colloidal particle in the
nanofluid. This layer is composed of ions that are charged opposite to the particle
surface and so form a charged diffuse layer over the particles. These ionic charges
are found to be forming due to the adsorption and desorption of ions present in the
solution on the particle surface (Cruz et al. 2005). These charged particles can then
transfer the charge and behave as charge carriers. In a nanofluid, the nanoparticles
act as carriers of electrical charge. The electrical double layer (EDL) has also found
to be one of the mechanisms responsible for the electrical transport properties of the
nanofluids by many researchers (Chakraborty and Padhy 2008; Ganguly et al. 2009;
Minea and Luciu 2012).
4.1 Measurement of Electrical Conductivity of the Nanofluids
Electrical conductivity of nanofluids has mostly been measured by researchers all
around the world by using electrical conductivity metre consisting of a probe, whose
electrical circuit with the circular electrode that makes up the working principle of the
electrical conductivity metre is shown in Fig. 9a. The one shown in Fig. 9b is a typical
electrical conductivity measuring device known as a four-cell conductivity electrode
metre (CyberScan CON 11) made by Eutech Instruments Pte Ltd in Singapore having
in-built automatic temperature compensation (ATC). This metre gives instant value
of electrical conductivity and temperature.
4.2 Factors Affecting the Electrical Conductivity
of the Nanofluids
Electrical conductivity being the property dependent on the components of the
nanofluid can be affected by many factors. As discussed earlier, the electrical conductivity of the nanofluids is dependent on the charge over the particles. They can also be
dependent on the amount and size of these charge carriers, that is, the nanoparticles.
These charges on the nanoparticles are dependent on the pH (Sigmund et al. 2000).