22
D. P. Barai et al.
studied the Al 2 O 3 /water nanofluid in a direct absorber solar collector (DASC) of
tube-in-plate type. The reported increase in the collector efficiency was 8.1% when
0.005 vol.% Al 2 O 3 /water nanofluid was passed through the DASC at a flowrate of
1.5 l/min. Sokhansefat et al. (2014) investigated the simulation of performance of
Al 2 O 3 nanofluid using synthetic oil as a basefluid in a parabolic trough collector
tube and suggested a possible and beneficial application of it in the solar thermal
energy collection in a parabolic trough geometry. Experimental study of CuO/water
nanofluid application in a direct absorption concentrating parabolic solar collector
(DAPSC) was reported to exhibit an increase in the thermal efficiency of 52% for
CuO/water nanofluid with volume concentration of 0.008 vol.% (Menbari et al.
2016).
Nanofluids have also found to have gained pace in applications in refrigeration
systems. Kumaresan et al. (2012) experimentally investigated convective heat transfer using MWCNT-based nanofluid as a secondary refrigerant using water/ethylene
glycol mixture as basefluid in a tubular heat exchanger. An enhancement of nearly
160% was found to be occurring by the use of 0.45 vol.% of the MWCNT-based
nanofluids, which was reportedly happening due to the higher thermal conductivity,
larger aspect ratio of the nanoparticles, particles rearrangement and delayed development of boundary layer. Similar study using single-walled carbon nanotubes-based
(SWCNT) nanofluid has been conducted by Vasconcelos et al. (2017). Influence of
shape of ZnO-based nanorefrigerant on the heat transfer using the refrigerant R-134a
as a basefluid is studied by Maheshwary et al. (2018). Spherical-shaped ZnO nanoparticles in the R-134a refrigerant found to exhibit a thermal conductivity enhancement
of the refrigerant by 25.26%. Thus, the thermal properties of the nanofluids have been
exploited in a numerous ways to make heat transfer processes more efficient with an
augmentation in the thermal transport caused by the presence of nanoparticles in the
nanofluid.
4 Electrical Conductivity of Nanofluids
Nanofluids are well known in the field of heat transfer as numerous researchers have
already studied its heat transfer characteristics and have reported several applications
of the nanofluids in thermal transport system as seen earlier in this chapter. But
there are several other properties of nanofluids that cannot be ignored. One of them
is the electrical conductivity of the nanofluids. As known already, the electrical
conductivity is the ability to transport or conduct electric current. Awareness about
the fact that the nanofluid may have superior electrical conductivity values than
other materials makes one to analyse it and apply a certain nanofluid in a typical
system which require fluids that conduct electrical energy. As the nanofluids possess
higher thermal conductivity, it is possible for them to also possess higher electrical
conductance.
Maxwell (1881) has very well defined that the electrical conductivity is affected by
the physical properties of the nanoparticles and the basefluid. But many researchers
D. P. Barai et al.
studied the Al 2 O 3 /water nanofluid in a direct absorber solar collector (DASC) of
tube-in-plate type. The reported increase in the collector efficiency was 8.1% when
0.005 vol.% Al 2 O 3 /water nanofluid was passed through the DASC at a flowrate of
1.5 l/min. Sokhansefat et al. (2014) investigated the simulation of performance of
Al 2 O 3 nanofluid using synthetic oil as a basefluid in a parabolic trough collector
tube and suggested a possible and beneficial application of it in the solar thermal
energy collection in a parabolic trough geometry. Experimental study of CuO/water
nanofluid application in a direct absorption concentrating parabolic solar collector
(DAPSC) was reported to exhibit an increase in the thermal efficiency of 52% for
CuO/water nanofluid with volume concentration of 0.008 vol.% (Menbari et al.
2016).
Nanofluids have also found to have gained pace in applications in refrigeration
systems. Kumaresan et al. (2012) experimentally investigated convective heat transfer using MWCNT-based nanofluid as a secondary refrigerant using water/ethylene
glycol mixture as basefluid in a tubular heat exchanger. An enhancement of nearly
160% was found to be occurring by the use of 0.45 vol.% of the MWCNT-based
nanofluids, which was reportedly happening due to the higher thermal conductivity,
larger aspect ratio of the nanoparticles, particles rearrangement and delayed development of boundary layer. Similar study using single-walled carbon nanotubes-based
(SWCNT) nanofluid has been conducted by Vasconcelos et al. (2017). Influence of
shape of ZnO-based nanorefrigerant on the heat transfer using the refrigerant R-134a
as a basefluid is studied by Maheshwary et al. (2018). Spherical-shaped ZnO nanoparticles in the R-134a refrigerant found to exhibit a thermal conductivity enhancement
of the refrigerant by 25.26%. Thus, the thermal properties of the nanofluids have been
exploited in a numerous ways to make heat transfer processes more efficient with an
augmentation in the thermal transport caused by the presence of nanoparticles in the
nanofluid.
4 Electrical Conductivity of Nanofluids
Nanofluids are well known in the field of heat transfer as numerous researchers have
already studied its heat transfer characteristics and have reported several applications
of the nanofluids in thermal transport system as seen earlier in this chapter. But
there are several other properties of nanofluids that cannot be ignored. One of them
is the electrical conductivity of the nanofluids. As known already, the electrical
conductivity is the ability to transport or conduct electric current. Awareness about
the fact that the nanofluid may have superior electrical conductivity values than
other materials makes one to analyse it and apply a certain nanofluid in a typical
system which require fluids that conduct electrical energy. As the nanofluids possess
higher thermal conductivity, it is possible for them to also possess higher electrical
conductance.
Maxwell (1881) has very well defined that the electrical conductivity is affected by
the physical properties of the nanoparticles and the basefluid. But many researchers