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D. P. Barai et al.
solid–liquid suspensions as practical heat transfer fluids. The rise of nanotechnology
has created the possibility of producing nanoparticles which are characterized by the
particle sizes below 100 nm. Nanofluids, a new group of heat transfer fluids, acquired
by dispersing and suspending nanoparticles with typical dimensions of the order of
1–100 nm were found by Choi (1995). The main objective behind using nanofluids
is to attain higher thermal properties and uniform and stable dispersions of nanoparticles. In order to achieve this objective, it becomes essential to understand how
nanoparticles intensify energy transport in liquids. Since Choi (1995) formulated
this new concept of nanofluids, many scientists expeditiously developed nanofluids
and found scientific facts not only on enhanced thermal properties of nanofluids, but
signifying new mechanisms that play major role in enhancing the thermal properties
of nanofluids and expanding new mathematical models for the nanofluids. The type
of nanoparticle, its size, shape and distribution are dominant properties that cannot
be effortlessly measured but affect the thermal transport properties of the nanofluids.
Other important factors include type of basefluids used, the method for the preparation of nanofluid, usage of surfactants and dispersing additives, pH, temperature,
viscosity and other physical properties. Two nanofluid samples with different type of
nanoparticles and amount of surfactants and/or pH adjusters while keeping all other
parameters constant may result in different thermo-physical properties.
Many researchers have studied nanofluids containing Al 2 O 3 nanoparticles (Heyhat et al. 2013; Sokhansefat et al. 2014; Usri et al. 2015), Cu nanoparticles (Eastman
et al. 2001; Yu et al. 2010) or carbon nanotubes (CNTs) (Jiang et al. 2015; Leong et al.
2016) and found remarkable increase in thermal conductivities. Hence, nanofluids
have gained attention in various heat transfer applications. There are various possible applications of nanofluids, which include transportation (engine cooling/vehicle
thermal management) (Azimi and Ommi 2013; Sidik et al. 2017), electronics cooling (Khaleduzzaman et al. 2015; Roberts and Walker 2010), nuclear systems cooling (Mahmud et al. 2016), heat exchangers (Bozorgan and Shafahi 2017; Li et al.
2018), fuel cell (Islam et al. 2015; Zakaria et al. 2016), solar water heating (Kasaeian
et al. 2015), chillers (Liu et al. 2011), lubricants (Mao et al. 2014), thermal storage
(Harikrishnana et al. 2013); (Chieruzzi et al. 2013) and many others.
As the thermal transport properties have been largely studied, researchers then
turned towards finding and analysing the electrical conducting properties of the
nanofluids. Maxwell’s model (Maxwell 1881) is found to be the pioneer in determining the electrical conductivity of the nanofluids theoretically based on the physical
properties of the nano-sized particles and basefluid. These properties of the nanofluids are affected by many factors, one of which is the particle size distribution of the
nano-sized particles in the nanofluids. Particle size distribution gives the amount of
particles according to their sizes present in the nanofluid. It is basically the degree to
which the sizes of the particles vary throughout the nanofluid. In a nanofluid, the dispersed nanoparticles are never of equal size and so its size distribution characterizes
the nanofluid better than any exact value of size of the nanoparticles. This property is
affected by many factors and affects other properties which are also discussed in this
chapter. Several studies on nanofluids depicting the values of thermal conductivity,
electrical conductivity as well as particle size are given in Table 1.
D. P. Barai et al.
solid–liquid suspensions as practical heat transfer fluids. The rise of nanotechnology
has created the possibility of producing nanoparticles which are characterized by the
particle sizes below 100 nm. Nanofluids, a new group of heat transfer fluids, acquired
by dispersing and suspending nanoparticles with typical dimensions of the order of
1–100 nm were found by Choi (1995). The main objective behind using nanofluids
is to attain higher thermal properties and uniform and stable dispersions of nanoparticles. In order to achieve this objective, it becomes essential to understand how
nanoparticles intensify energy transport in liquids. Since Choi (1995) formulated
this new concept of nanofluids, many scientists expeditiously developed nanofluids
and found scientific facts not only on enhanced thermal properties of nanofluids, but
signifying new mechanisms that play major role in enhancing the thermal properties
of nanofluids and expanding new mathematical models for the nanofluids. The type
of nanoparticle, its size, shape and distribution are dominant properties that cannot
be effortlessly measured but affect the thermal transport properties of the nanofluids.
Other important factors include type of basefluids used, the method for the preparation of nanofluid, usage of surfactants and dispersing additives, pH, temperature,
viscosity and other physical properties. Two nanofluid samples with different type of
nanoparticles and amount of surfactants and/or pH adjusters while keeping all other
parameters constant may result in different thermo-physical properties.
Many researchers have studied nanofluids containing Al 2 O 3 nanoparticles (Heyhat et al. 2013; Sokhansefat et al. 2014; Usri et al. 2015), Cu nanoparticles (Eastman
et al. 2001; Yu et al. 2010) or carbon nanotubes (CNTs) (Jiang et al. 2015; Leong et al.
2016) and found remarkable increase in thermal conductivities. Hence, nanofluids
have gained attention in various heat transfer applications. There are various possible applications of nanofluids, which include transportation (engine cooling/vehicle
thermal management) (Azimi and Ommi 2013; Sidik et al. 2017), electronics cooling (Khaleduzzaman et al. 2015; Roberts and Walker 2010), nuclear systems cooling (Mahmud et al. 2016), heat exchangers (Bozorgan and Shafahi 2017; Li et al.
2018), fuel cell (Islam et al. 2015; Zakaria et al. 2016), solar water heating (Kasaeian
et al. 2015), chillers (Liu et al. 2011), lubricants (Mao et al. 2014), thermal storage
(Harikrishnana et al. 2013); (Chieruzzi et al. 2013) and many others.
As the thermal transport properties have been largely studied, researchers then
turned towards finding and analysing the electrical conducting properties of the
nanofluids. Maxwell’s model (Maxwell 1881) is found to be the pioneer in determining the electrical conductivity of the nanofluids theoretically based on the physical
properties of the nano-sized particles and basefluid. These properties of the nanofluids are affected by many factors, one of which is the particle size distribution of the
nano-sized particles in the nanofluids. Particle size distribution gives the amount of
particles according to their sizes present in the nanofluid. It is basically the degree to
which the sizes of the particles vary throughout the nanofluid. In a nanofluid, the dispersed nanoparticles are never of equal size and so its size distribution characterizes
the nanofluid better than any exact value of size of the nanoparticles. This property is
affected by many factors and affects other properties which are also discussed in this
chapter. Several studies on nanofluids depicting the values of thermal conductivity,
electrical conductivity as well as particle size are given in Table 1.