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Abstract:
The enhanced thermal properties being the prominent objective behind the
usage of nanofluids. Hence it is necessary to study the base/nanofluid
physical properties at various conditions. This article projects the
experimental results of thermal conductivity and viscosity of two
different nanofluids. The ratio was considered as 60:40 and 40:40 by
volume in water and ethylene glycol respectively. The preparation of
nanofluids was started by scattering SiO2 nano-particles in EG and
“water” (W) blended in “60:40” (60EGW) and “40:60” (40EGW) ratio
by volume. The ratio was considered as 60:40 and 40:40 by volume in
water and ethylene glycol respectively. The regression analysis was
conducted with available data and correlations were formulated for
thermal properties. The nanofluids were used in evaluating “viscosity”
and “thermal conductivity” experimentally. From the results, the SiO2
particles have achieved enhancement of 34% and 32% in thermal
conductivity with the two base-fluids. Similarly, enhancement of 102%
and 62% were reported in viscosity. Hence, it can be observed that SiO2
nanofluids in 40EGW nanofluid are a better heat transfer fluid when
compared to SiO2 in 60EGW nanofluid.
Keywords: Nano-fluids; Base-fluids; Heat transfer analysis;
Nano-particles; Silicon dioxide; Thermal conductivity, Viscosity
Introduction:
Some of the renowned conventional working fluids include refrigerants,
oil, glycol, ethylene, and water. Indeed, nanofluids, which represent
new fluid trends, can be used to enhance these conventional working
fluids’ characteristics. Imperative to note is that nanofluids
constitute nano-sized solid particle suspensions, which are found in
liquids and have their sizes ranging between 1 nm to 100 nm. Some of the
applications in which the new particles (nanofluids) could gain
application include manufactured drug delivery systems, solar water
heating, thermal storage, lubrications, drilling, refrigeration, cooling
electronics, engine oil transmissions, and engine cooling [1–4].
Some of the enhanced thermal properties with which nanofluids are
associated, which account for their increasing application, include heat
transfer[5], thermal conductivity[6,7], specific heat
conductivity[8], viscosity[9], and density [10]. With
enhanced thermal conductivity, the eventuality is that there is likely
to be a state of enhanced heat transfer. These mixed, but promising
outcomes point to the criticality of examining the nanofluids and base
fluids’ thermal physical properties at different experimental or
operating conditions [11–13].
Several scholarly investigations have been conducted to understand the
extent to which there could be enhanced convective heat transfer,
especially regarding the use of different nano particles [14–20].
Some of the particles that have been investigated included Silicon
Dioxide, Titanium Dioxide, Zinc Oxide, Copper Oxide, and Aluminum
Dioxide. Upon dispersing these nano particles in water, most of the
outcomes suggest good results. Apart from water as a base fluid that has
been used, other materials that have continually been embraced included
glycerin, ethylene glycol, and oil. In situations where the volume of
water and ethylene glycol mixtures as base fluids has been set at 40:60
(40EGW) and 60:40 (60 EGW), promising results have been reported. An
enhancement of 40% was observed by Vajjha [21] for a particle
concentration varying from 1.0%-10.0% concertation range and 0oC to 100 oC temperature range for
60EGW and 24% enhancement was observed by Azmi [22] for a particle
concentration less than 1.0% at a working temperature of
70oC in 40EGW base fluids.
One of the prominent steps involves nanofluids preparation with
stability, especially in relation to their application for industrial
scale, the step remains challenging. From the previous investigation,
the nano particles’ setting behavior accounts for the perceived
challenges [23–26]. Two procedures through which nanofluids tend to
be prepared include the two-step process, as well as the one-step
process. In this investigation, the method that was used in nanofluids
preparation entailed the two-step procedure. To modulate the stability
of the materials that were used, the study relied on the aspect of pH
control whereby the shape and size of the nano particles were controlled
[27,28] similarly, the surfactant and dispersant were selected
appropriately [29]. It is also imperative to highlight that
different methods for dispersing nanofluids exist. Some of these
techniques include homogenization, ultrasonication, and ball mining,
which have an impact on the stability scenario [30,31].
In the aspect of heat transfer coefficient, one of the notable
parameters that play an important role entails the target fluid’s state
of thermal conductivity. From the majority of the previous experimental
investigations, factors that affect the thermal conductivity of
nanofluids include dispersion, the pH value, temperature, shape, size,
volume concentration, and the base liquid; as well as material
properties [32]. The transient hot-wire technique is mostly used to
measure the state of thermal conductivity because of its high accuracy
and quick response time – with the KD2 Pro instrument also playing a
complementary role in realizing the merits. It is also notable that most
of the previous experiments have seen the viscosity measured using
viscometers. To take the viscosity readings, this investigation relied
on the Anton Paar MCR 302 Rheometer. Given the shear rates, this tool
determines the state of parameters such as viscosity and the shear
stress.
In the experimental investigation by Namburu et al. [33], different
particle sizes were used as the dependent variables for discerning the
viscosities of SiO2 nanoparticles, hence a comparative
analysis. The selected sizes included 100, 50, and 20 nm. These
particles were dispersed in 60EGW while the range reflecting the
concentration was between 0% and 10%. Also, the temperature range was
between -36oC and +50oC. From the
findings, the study indicated that at 8% concentration and with 100
nm-sized nano particles, SiO2 nanofluids exhibit the
least velocity. In another investigation by Sundar et al. [34] in
their experiments, investigated the influence of various EG/water base
liquid mixture ratio , the main objective was to determine the impact of
different water/EB base fluid mixture ratios on the viscosity of
nanofluids; with particular reference to 60:40%, 40:60%, and 20:80%
ratios by weight; having suspended the materials in
Al2O3 nano particles. The range of
temperature for these experimental conditions involved
20oC to 60oC. Also, Vajjha and Das
[35] strived to unearth the state of thermal conductivity of
different nanofluids. With the particle dispersal operating at 60EGW
relative to the mass ratio, specific nanofluids that were investigated
included ZnO, CuO and Al2O3. The range
of temperature under which the experimental conditions were set was
between 25oC and 90oC. Also, 10%
was the maximum volume concentration under which the experimental study
was conducted. The authors formulated a new relationship or correlation
linked to \(\beta_{1}\) and\(f\left(T,\phi\right)\), which was
expressed in the form:
\(f\left(T,\phi\right)=\left(2.8217\times 10^{-2}\phi+3.917\times 10^{-3}\right)\left(\frac{T}{T_{o}}\right)+(-3.0669\times 10^{-2}\phi-\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 3.91123\times 10^{-3})\)(1)
The relations for \(\beta_{1}\) are listed in Table 1 for
different nanofluids.