Synthesis and Characterization of Nanofluids …
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concentrations, which ultimately lead to a high electrical conductivity. However,
Glover et al. (2008) reported that there is no percolation threshold for SWNT-based
aqueous nanofluids and that there is a linear relationship between the electrical conductivity and the concentration depicting ionic conduction behaviour. The electrical
conductivity of the water-based single-walled carbon nanotube (SWNT) nanofluids
reported to be increased from 0.12 × 10
−3 to 1.6 × 10
−3 S/m when nanofluid concentration increases from 0 to 0.5 wt%, which was around 13 times more. It was
shown for alumina nanofluids that the electrical conductivity also linearly increases
with increase in the concentration of the nanofluid by Ganguly et al. (2009) and it
was recorded to be 258 μS/cm for nanofluid volume fraction of 0.03 at room temperature. An enhancement of electrical conductivity exhibited by graphene-based
nanofluids using mixture of water and ethylene glycol as basefluids was studied
by Baby and Ramaprabhu (2010). They found that a 0.03% concentrated graphene
nanofluid shows an electrical conductivity enhancement of almost 1400% at 25 °C. A
973 times higher electrical conductivity was recorded by Shen et al. (2012) by adding
ZnO nanoparticles to insulating oil at a concentration of 0.75 vol.%. An outstanding enhancement of 25678% in electrical conductivity was recorded by Hadadian
et al. (2014) for water-based graphene oxide nanofluid at a very low graphene oxide
mass fraction of 0.0006. Electrical conductivity of nitrogen-doped graphene-based
nanofluids was studied by Mehrali et al. (2015) and they found a maximum electrical conductivity enhancement of 1814.96% for a 0.06 wt% nanofluid. Adio et al.
(2015a) investigated the effect of volume fraction on the electrical conductivity of
MgO-based nanofluids using ethylene glycol as basefluids. For the MgO nanofluid
concentrations of 0.1, 0.5, 1, 2 and 3 vol.%, the electrical conductivity was found
to be 3.01, 6.68, 8.73, 11.74 and 14.05 μS/cm, respectively. Al 2 O 3 nanofluids prepared using bio-glycol/water mixtures as basefluid were studied by Abdolbaqi et al.
(2016) and they found a decrease in electrical conductivity with an increase in the
concentration of the nanofluid. A nanofluid prepared using bio-glycol/water mixture
in the ratio of 40:60 by volume showed a decrease in electrical conductivity from
620 to 472 μS/cm when the concentration of Al 2 O 3 nanoparticles increased from 0
to 2 vol.%. It has been found that the effect of nanoparticle concentration is more
pronounced than that of temperature on the electrical conductivity of the nanofluids
(Heyhat and Irannezhad 2018).
4.2.2 Size of Nanoparticles
Sarojini et al. (2013) studied that for alumina nanoparticles, the reduction in particle
size leads to an increment in the electrical conductivity of the nanofluids in which
they are dispersed. This is found to be happening due to the higher electrophoretic
mobility of the smaller-sized particles compared to the larger-sized particles. A 1
vol.% alumina nanofluid prepared using water as a basefluid show electrical conductivity of nearly 95, 240 and 300 μS/cm for dispersed nanoparticles of size 150, 80
and between 20 and 30 nm, respectively.
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concentrations, which ultimately lead to a high electrical conductivity. However,
Glover et al. (2008) reported that there is no percolation threshold for SWNT-based
aqueous nanofluids and that there is a linear relationship between the electrical conductivity and the concentration depicting ionic conduction behaviour. The electrical
conductivity of the water-based single-walled carbon nanotube (SWNT) nanofluids
reported to be increased from 0.12 × 10
−3 to 1.6 × 10
−3 S/m when nanofluid concentration increases from 0 to 0.5 wt%, which was around 13 times more. It was
shown for alumina nanofluids that the electrical conductivity also linearly increases
with increase in the concentration of the nanofluid by Ganguly et al. (2009) and it
was recorded to be 258 μS/cm for nanofluid volume fraction of 0.03 at room temperature. An enhancement of electrical conductivity exhibited by graphene-based
nanofluids using mixture of water and ethylene glycol as basefluids was studied
by Baby and Ramaprabhu (2010). They found that a 0.03% concentrated graphene
nanofluid shows an electrical conductivity enhancement of almost 1400% at 25 °C. A
973 times higher electrical conductivity was recorded by Shen et al. (2012) by adding
ZnO nanoparticles to insulating oil at a concentration of 0.75 vol.%. An outstanding enhancement of 25678% in electrical conductivity was recorded by Hadadian
et al. (2014) for water-based graphene oxide nanofluid at a very low graphene oxide
mass fraction of 0.0006. Electrical conductivity of nitrogen-doped graphene-based
nanofluids was studied by Mehrali et al. (2015) and they found a maximum electrical conductivity enhancement of 1814.96% for a 0.06 wt% nanofluid. Adio et al.
(2015a) investigated the effect of volume fraction on the electrical conductivity of
MgO-based nanofluids using ethylene glycol as basefluids. For the MgO nanofluid
concentrations of 0.1, 0.5, 1, 2 and 3 vol.%, the electrical conductivity was found
to be 3.01, 6.68, 8.73, 11.74 and 14.05 μS/cm, respectively. Al 2 O 3 nanofluids prepared using bio-glycol/water mixtures as basefluid were studied by Abdolbaqi et al.
(2016) and they found a decrease in electrical conductivity with an increase in the
concentration of the nanofluid. A nanofluid prepared using bio-glycol/water mixture
in the ratio of 40:60 by volume showed a decrease in electrical conductivity from
620 to 472 μS/cm when the concentration of Al 2 O 3 nanoparticles increased from 0
to 2 vol.%. It has been found that the effect of nanoparticle concentration is more
pronounced than that of temperature on the electrical conductivity of the nanofluids
(Heyhat and Irannezhad 2018).
4.2.2 Size of Nanoparticles
Sarojini et al. (2013) studied that for alumina nanoparticles, the reduction in particle
size leads to an increment in the electrical conductivity of the nanofluids in which
they are dispersed. This is found to be happening due to the higher electrophoretic
mobility of the smaller-sized particles compared to the larger-sized particles. A 1
vol.% alumina nanofluid prepared using water as a basefluid show electrical conductivity of nearly 95, 240 and 300 μS/cm for dispersed nanoparticles of size 150, 80
and between 20 and 30 nm, respectively.