Synthesis and Characterization of Nanofluids …
39
nanofluid concentration of 0.55 vol.%. A similar size distribution is also obtained
by using CTAB in 1 vol.% Cu nanofluid. But when oleic acid is used for dispersing
same concentration of Cu nanoparticles in water, a substantial increase in the size of
the particles is observed and the size distribution shifted to higher ranges exhibiting
an average particle size of 800 nm. This was reported to be happening due to the
heavy agglomeration of the nanoparticles due to inefficiency of oleic acid to keep
them de-agglomerated and its failure in producing stable nanofluid.
5.2.4 Temperature
The temperatures, as known earlier, tend to affect the surface charges of the particles,
which may affect their tendency to agglomerate. Also, the Brownian motion of the
particles is greatly affected by temperature, which may have an indirect effect on the
particle size. It was found by Suganthi and Rajan (2012) for ZnO-based nanofluids
that the average particle hydrodynamic size increases with increase in temperature
of the nanofluid. This was found to be happening due to the increase in Brownian
motion of the particles. They prepared water-based ZnO nanofluids using sodium
hexametaphosphate (SHMP) as a stabilizing agent. The adsorption of PO
3− ions
generated due to dissociation of SHMP when dissolved in water on the surface of
the ZnO nanoparticles reduces their agglomeration. This chemisorption of the PO
3−
ions over the surface of the particles is a function of temperature and so an increase
in the temperature resulted in the shift of the equilibrium of this exothermic adsorption towards desorption which is favourable at higher temperatures. Ultimately, this
process leads to production of vacant sites on the surface of the ZnO nanoparticles,
facilitating particle–particle interaction and thus agglomeration of the nanoparticles.
Being dependent on the equilibrium of the adsorption of the PO
3− ions, this process
is reversible and so restoration of the PO
3− ions took place as the temperature of
the nanofluid was decreased and the difference between the particle size during the
heating and cooling cycle was 2 nm at 25 °C.
5.3 Influence of Particle Size Distribution on Properties
of Nanofluids
Particle size distribution of nanofluids determines whether the nanofluid is monodisperse or polydisperse. Size of the particles dispersed in the nanofluid impacts a lot
of thermo-physical properties of the nanofluid. Below is given how the particle size
distribution affects the thermal and optical properties of nanofluids.
39
nanofluid concentration of 0.55 vol.%. A similar size distribution is also obtained
by using CTAB in 1 vol.% Cu nanofluid. But when oleic acid is used for dispersing
same concentration of Cu nanoparticles in water, a substantial increase in the size of
the particles is observed and the size distribution shifted to higher ranges exhibiting
an average particle size of 800 nm. This was reported to be happening due to the
heavy agglomeration of the nanoparticles due to inefficiency of oleic acid to keep
them de-agglomerated and its failure in producing stable nanofluid.
5.2.4 Temperature
The temperatures, as known earlier, tend to affect the surface charges of the particles,
which may affect their tendency to agglomerate. Also, the Brownian motion of the
particles is greatly affected by temperature, which may have an indirect effect on the
particle size. It was found by Suganthi and Rajan (2012) for ZnO-based nanofluids
that the average particle hydrodynamic size increases with increase in temperature
of the nanofluid. This was found to be happening due to the increase in Brownian
motion of the particles. They prepared water-based ZnO nanofluids using sodium
hexametaphosphate (SHMP) as a stabilizing agent. The adsorption of PO
3− ions
generated due to dissociation of SHMP when dissolved in water on the surface of
the ZnO nanoparticles reduces their agglomeration. This chemisorption of the PO
3−
ions over the surface of the particles is a function of temperature and so an increase
in the temperature resulted in the shift of the equilibrium of this exothermic adsorption towards desorption which is favourable at higher temperatures. Ultimately, this
process leads to production of vacant sites on the surface of the ZnO nanoparticles,
facilitating particle–particle interaction and thus agglomeration of the nanoparticles.
Being dependent on the equilibrium of the adsorption of the PO
3− ions, this process
is reversible and so restoration of the PO
3− ions took place as the temperature of
the nanofluid was decreased and the difference between the particle size during the
heating and cooling cycle was 2 nm at 25 °C.
5.3 Influence of Particle Size Distribution on Properties
of Nanofluids
Particle size distribution of nanofluids determines whether the nanofluid is monodisperse or polydisperse. Size of the particles dispersed in the nanofluid impacts a lot
of thermo-physical properties of the nanofluid. Below is given how the particle size
distribution affects the thermal and optical properties of nanofluids.