Figure 8 Comparison of experimental thermal conductivity values of base
fluids with ASHRAE data
Nanofluid correlations in (13) were compared with thermal conductivity
values obtained regarding this study’s selected nanofluids. With the
temperature range set between 25oC and
60oC and the concentrations for
SiO2/60EGW nanofluids set at 1.5%, 1.0% and 0.5%,
Figure 9 highlights the outcomes. In the investigation, an additional
experimental condition was that the particle size was set at 20nm.
Indeed, 15% was observed as a maximum deviation experienced.
Imperatively, thermal conductivity was reduced via the addition of
higher thermal conductivity particles. Indeed, the temperature of the
nanofluids was observed to be a key parameter affecting the thermal
conductivity of the selected materials. In particular, it was
established that an increase in temperature causes an increase in the
state of thermal conductivity, reflecting a direct correlation between
the factor of temperature and the aspect of thermal conductivity.
The nanofluid thermal conductivity was plotted against temperature along
with correlation (15) for the given nanofluid SiO2/40EGW
and was shown in Figure 10 for the similar operating conditions
as mentioned for 60EGW based nanofluids.The maximum deviation observed
12% when compared to the base fluid 40EGW.
Compared to water, it was evident that ethylene glycol exhibits low
thermal conductivity. Hence, adding the ethylene glycol to water would
cause water’s thermal conductivity suppression. As more ethylene glycol
is added, the thermal conductivity of the resultant mixture would
reduce. These results were not only obtained in this study but had also
been reported in part of the previous literature [22]; especially
for scholarly studies that had targeted or focused on
Al2O3/40EGW nanofluids.