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D. P. Barai et al.
5.2.2 Concentration of Nanoparticles in Nanofluid
The concentration of the nanoparticles affects the particle size distribution of the
nanoparticles in the nanofluid in a way that a large quantity of nanoparticles may
form larger agglomerates and broaden the particle size distribution. Colla et al. (2014)
prepared ZnO nanofluids and studied the effect of concentration on the intensity of
size distribution of the particles in the nanofluid. They found that the intensity of
particles in the narrow range increases as the ZnO nanofluid concentration increases
from 1 to 5%. But the intensity again decreases as the nanofluid concentration further
increases to 10% which can be due to the agglomeration of the some particles and
formation of larger size particles, thus broadening the size distribution curve. Juneja
and Gangacharyulu (2017) studied the effect of concentration of particle size distribution of Al 2 O 3 -based nanofluid prepared using distilled water, ethylene glycol and
mixture of water/ethylene glycol (in the ratio 75:25). They prepared Al 2 O 3 nanofluids in the volume fraction range of 0.1–1%. For water-based Al 2 O 3 nanofluids, the
mean diameter of the nanoparticles first increased till a volume concentration of 0.25
vol.% and then showed a decreasing trend till 1% nanofluid concentration. The one
prepared using ethylene glycol as a basefluid showed a straight decrease in the mean
diameter of Al 2 O 3 nanoparticles, while the nanofluid prepared in water/ethylene glycol mixture as a basefluid exhibited no change in the mean diameter after increasing
the nanofluid concentration above 0.5 vol.%.
5.2.3 Addition of Surfactants
Surfactants in the nanofluids play an important role in the dispersion of the nanoparticles and in preventing formation of agglomerates. Wang et al. (2009) studied the
effect of addition of sodium dodecylbenzene sulfonate (SDBS) surfactant on the
particle size distribution of Al 2 O 3 and Cu nanoparticle in water-based nanofluids.
They found that the presence of SDBS shifts the whole size distribution curve of
both the nanofluids prepared at 0.05 wt% concentration to lower particle size range.
In a similar study, Das et al. (2016) found that the TiO 2 –water nanofluids can be
well stabilized using acetic acid and cetyl trimethylammonium bromide (CTAB) as
dispersants. They purchased 21 nm-sized TiO 2 nanoparticles, but their dispersion in
water produced nanofluid containing average particle diameter of 147.6 and 207.7 nm
with surfactants acetic acid and CTAB, respectively, at respective nanofluid concentrations of 1.5 and 1 vol.%. The higher size of the particles detected in the nanofluid
occurred due to thermodynamically stable TiO 2 nanoparticle cluster formed in the
nanofluid.
Saterlie et al. (2011) conducted a comparative study of the effect of two types
of surfactants, namely cetyl trimethylammonium bromide (CTAB) and oleic acid,
on the particle size distribution of Cu nanoparticles in water-based nanofluids at
0.55 and 1 vol.% concentrations of the nanoparticles. They observed that oleic acid
and CTAB are able to produce Cu nanofluids with particle size distribution at lower
ranges having an average particle size of nearly 120 and 80 nm, respectively, at a
D. P. Barai et al.
5.2.2 Concentration of Nanoparticles in Nanofluid
The concentration of the nanoparticles affects the particle size distribution of the
nanoparticles in the nanofluid in a way that a large quantity of nanoparticles may
form larger agglomerates and broaden the particle size distribution. Colla et al. (2014)
prepared ZnO nanofluids and studied the effect of concentration on the intensity of
size distribution of the particles in the nanofluid. They found that the intensity of
particles in the narrow range increases as the ZnO nanofluid concentration increases
from 1 to 5%. But the intensity again decreases as the nanofluid concentration further
increases to 10% which can be due to the agglomeration of the some particles and
formation of larger size particles, thus broadening the size distribution curve. Juneja
and Gangacharyulu (2017) studied the effect of concentration of particle size distribution of Al 2 O 3 -based nanofluid prepared using distilled water, ethylene glycol and
mixture of water/ethylene glycol (in the ratio 75:25). They prepared Al 2 O 3 nanofluids in the volume fraction range of 0.1–1%. For water-based Al 2 O 3 nanofluids, the
mean diameter of the nanoparticles first increased till a volume concentration of 0.25
vol.% and then showed a decreasing trend till 1% nanofluid concentration. The one
prepared using ethylene glycol as a basefluid showed a straight decrease in the mean
diameter of Al 2 O 3 nanoparticles, while the nanofluid prepared in water/ethylene glycol mixture as a basefluid exhibited no change in the mean diameter after increasing
the nanofluid concentration above 0.5 vol.%.
5.2.3 Addition of Surfactants
Surfactants in the nanofluids play an important role in the dispersion of the nanoparticles and in preventing formation of agglomerates. Wang et al. (2009) studied the
effect of addition of sodium dodecylbenzene sulfonate (SDBS) surfactant on the
particle size distribution of Al 2 O 3 and Cu nanoparticle in water-based nanofluids.
They found that the presence of SDBS shifts the whole size distribution curve of
both the nanofluids prepared at 0.05 wt% concentration to lower particle size range.
In a similar study, Das et al. (2016) found that the TiO 2 –water nanofluids can be
well stabilized using acetic acid and cetyl trimethylammonium bromide (CTAB) as
dispersants. They purchased 21 nm-sized TiO 2 nanoparticles, but their dispersion in
water produced nanofluid containing average particle diameter of 147.6 and 207.7 nm
with surfactants acetic acid and CTAB, respectively, at respective nanofluid concentrations of 1.5 and 1 vol.%. The higher size of the particles detected in the nanofluid
occurred due to thermodynamically stable TiO 2 nanoparticle cluster formed in the
nanofluid.
Saterlie et al. (2011) conducted a comparative study of the effect of two types
of surfactants, namely cetyl trimethylammonium bromide (CTAB) and oleic acid,
on the particle size distribution of Cu nanoparticles in water-based nanofluids at
0.55 and 1 vol.% concentrations of the nanoparticles. They observed that oleic acid
and CTAB are able to produce Cu nanofluids with particle size distribution at lower
ranges having an average particle size of nearly 120 and 80 nm, respectively, at a