20
D. P. Barai et al.
nanoparticles driven by Brownian motion, thermal diffusion in nano-sized particle
and fluids, and the thermal interaction of particle with fluid molecules, where Re d =
C RM d p
υ
in which C RM =
K B T
3πμ f d p l f
, d f is the equivalent diameter of particle and l f
mean free path.
k eff = k f (1 − ∅) + 0.01k p ∅ +
18 × 10
6
d f
d p
k f Re
2
d Pr f ∅
(17)
3.5 Applications Based on Thermal Properties
of the Nanofluids
As it has been well known that the nanofluids possess extraordinary thermal properties, compared with conventional fluids, there has also been a tremendous increase
in the studies for different applications of the nanofluids in numerous heat transfer systems. Several researchers have investigated the heat transfer intensification
of nanofluids by using different geometries of lab-scale heat exchanger setups and
have proposed a possible and feasible application of nanofluids as an alternative to
conventional heat transfer fluids. Heyhat et al. (2013) studied the convective heat
transfer performance of Al 2 O 3 nanofluids with water as basefluid flowing in a horizontal tube at constant wall temperature and laminar flow conditions. An increase
in the heat transfer coefficient was reported for the nanofluid compared to that of
basefluid and that it was further noticeable at higher Reynolds numbers. At fully
developed flow region, the improvement in heat transfer coefficient was reported
to be 32% for 2 vol.% of Al 2 O 3 nanofluid. Convective heat transfer performance
of TiO 2 /water nanofluid in a helical coiled tube heat exchanger has been studied
by Kahani et al. (2014). A thermal performance factor of 3.72 was achieved for 2
vol.% TiO 2 nanofluid flowing at Reynolds number of 1750. A heat transfer coefficient enhancement of 105% has been found by Bhanvase et al. (2014) for TiO 2 -based
nanofluid using ethylene glycol/water mixture as basefluid flowing in a straight tube
heat exchanger suggesting a great alternative for applications in heat transfer equipments. Huang et al. (2015) investigated the convective heat transfer and pressure drop
of Al 2 O 3 -based and multi-walled carbon nanotubes-based (MWCNT) nanofluid. A
higher heat transfer was achieved by using the nanofluids; however, increasing concentrations of the nanofluids increased the pressure drop. But, this was only found
to be happening at higher concentrations of nanofluid due to increased viscosity,
whereas viscosities of nanofluids with low concentrations did not seem to affect
the pressure drop due to negligible increase in viscosity as compared to the basefluid. Convective heat transfer coefficient of Fe 3 O 4 /graphene nanocomposite-based
nanofluid was found to enhance by 14.5% compared to the basefluid in a straight tube
heat exchanger by Askari et al. (2017). Bhanvase et al. (2018) investigated the boost
in heat transfer of polyaniline-based (PANI) nanofluids using water as a basefluid.
D. P. Barai et al.
nanoparticles driven by Brownian motion, thermal diffusion in nano-sized particle
and fluids, and the thermal interaction of particle with fluid molecules, where Re d =
C RM d p
υ
in which C RM =
K B T
3πμ f d p l f
, d f is the equivalent diameter of particle and l f
mean free path.
k eff = k f (1 − ∅) + 0.01k p ∅ +
18 × 10
6
d f
d p
k f Re
2
d Pr f ∅
(17)
3.5 Applications Based on Thermal Properties
of the Nanofluids
As it has been well known that the nanofluids possess extraordinary thermal properties, compared with conventional fluids, there has also been a tremendous increase
in the studies for different applications of the nanofluids in numerous heat transfer systems. Several researchers have investigated the heat transfer intensification
of nanofluids by using different geometries of lab-scale heat exchanger setups and
have proposed a possible and feasible application of nanofluids as an alternative to
conventional heat transfer fluids. Heyhat et al. (2013) studied the convective heat
transfer performance of Al 2 O 3 nanofluids with water as basefluid flowing in a horizontal tube at constant wall temperature and laminar flow conditions. An increase
in the heat transfer coefficient was reported for the nanofluid compared to that of
basefluid and that it was further noticeable at higher Reynolds numbers. At fully
developed flow region, the improvement in heat transfer coefficient was reported
to be 32% for 2 vol.% of Al 2 O 3 nanofluid. Convective heat transfer performance
of TiO 2 /water nanofluid in a helical coiled tube heat exchanger has been studied
by Kahani et al. (2014). A thermal performance factor of 3.72 was achieved for 2
vol.% TiO 2 nanofluid flowing at Reynolds number of 1750. A heat transfer coefficient enhancement of 105% has been found by Bhanvase et al. (2014) for TiO 2 -based
nanofluid using ethylene glycol/water mixture as basefluid flowing in a straight tube
heat exchanger suggesting a great alternative for applications in heat transfer equipments. Huang et al. (2015) investigated the convective heat transfer and pressure drop
of Al 2 O 3 -based and multi-walled carbon nanotubes-based (MWCNT) nanofluid. A
higher heat transfer was achieved by using the nanofluids; however, increasing concentrations of the nanofluids increased the pressure drop. But, this was only found
to be happening at higher concentrations of nanofluid due to increased viscosity,
whereas viscosities of nanofluids with low concentrations did not seem to affect
the pressure drop due to negligible increase in viscosity as compared to the basefluid. Convective heat transfer coefficient of Fe 3 O 4 /graphene nanocomposite-based
nanofluid was found to enhance by 14.5% compared to the basefluid in a straight tube
heat exchanger by Askari et al. (2017). Bhanvase et al. (2018) investigated the boost
in heat transfer of polyaniline-based (PANI) nanofluids using water as a basefluid.