14
D. P. Barai et al.
Fig. 5 Effect of volume fraction of Al 2 O 3 nanoparticles in Al 2 O 3 –ethylene glycol nanofluids on
relative thermal conductivity of the nanofluids (Esfe et al. 2015a)
3.3.4 Temperature
Temperature is found to be greatly influencing the thermal conductivity of a nanofluid
which is studied by several researchers. Mintsa et al. (2009) investigated the thermal
conductivity of Al 2 O 3 and CuO-based nanofluids as a function of temperature and
reported an increase in thermal conductivity with rise in temperature for different size
of nanoparticles and concentrations of nanofluids. Increase in temperature increases
the nanoparticles’ surface energy leading to reduced agglomeration. Graphene, having attained most of the attention of the researchers, and its nanofluids have also found
to show an increase in thermal conductivity with temperature, which is reported by
Ahammed et al. (2016) at various concentrations of the nanofluid as shown in Fig. 6.
It was clear that the factors like vibration of phonons and free electrons and molecular collision and molecular diffusion jointly affect the thermal conductivity of the
graphene-based nanofluids.
One more reason behind the enhancement in the thermal conductivity with temperature is the increase in Brownian motion of the nanoparticles. Two factors responsible for this are the reduction of agglomeration of nanoparticles due to high surface
energy at high temperatures and the reduction in viscosity of the basefluid which
again facilitates swift Brownian motion of the nanoparticles (Yu-Hua et al. 2008).
D. P. Barai et al.
Fig. 5 Effect of volume fraction of Al 2 O 3 nanoparticles in Al 2 O 3 –ethylene glycol nanofluids on
relative thermal conductivity of the nanofluids (Esfe et al. 2015a)
3.3.4 Temperature
Temperature is found to be greatly influencing the thermal conductivity of a nanofluid
which is studied by several researchers. Mintsa et al. (2009) investigated the thermal
conductivity of Al 2 O 3 and CuO-based nanofluids as a function of temperature and
reported an increase in thermal conductivity with rise in temperature for different size
of nanoparticles and concentrations of nanofluids. Increase in temperature increases
the nanoparticles’ surface energy leading to reduced agglomeration. Graphene, having attained most of the attention of the researchers, and its nanofluids have also found
to show an increase in thermal conductivity with temperature, which is reported by
Ahammed et al. (2016) at various concentrations of the nanofluid as shown in Fig. 6.
It was clear that the factors like vibration of phonons and free electrons and molecular collision and molecular diffusion jointly affect the thermal conductivity of the
graphene-based nanofluids.
One more reason behind the enhancement in the thermal conductivity with temperature is the increase in Brownian motion of the nanoparticles. Two factors responsible for this are the reduction of agglomeration of nanoparticles due to high surface
energy at high temperatures and the reduction in viscosity of the basefluid which
again facilitates swift Brownian motion of the nanoparticles (Yu-Hua et al. 2008).