Figure 4. pH values plotted
against temperature and time
Thermal conductivity and viscosity experimental
setup
As mentioned earlier, the Anton Paar MCR 302 Rheometer aided in taking
the viscosity readings. These readings aided in discerning viscosity and
shear stress, which were the fluid parameters at the selected shear
stresses. Indeed, the tool reflects an oscillatory and rotational
rheometer that gives insight into the viscoelastic or viscous
characteristic of different materials; including solids, gels, and
fluids.
To measure the selected samples’ thermal conductivity, the KD2 pro was
used. The instrument had a lab thermal properties analyzer, as well as a
fully portable field. Indeed, its functionality holds that the thermal
conductivity is measured using the transient line heat source –
relative to the IEEE and ASTM specifications. Also, the instrument
constitutes a small single needle (6 cm) and a digital controller.
Furthermore, it has special algorithms responsible for analyzing the
resultant measurements gained during cooling and heating intervals. In
this study, five consecutive measurements were used to obtain the
calibration data. Also important to note is that a 2.0-percent deviation
was observed. The times of reading the measurements ranged between one
and ten minute. The type of measurement determined the interval of
taking the readings.
3.1. Thermal Conductivity
Measurements for
Stability
Measuring the thermal conductivity of the given nanofluids is one of the
known methods to keep a check on stability. To have a better
understanding on knf and thermal conductivity
enhancements, it is important to follow the time dependent
knf,η of stable metal and metal oxide nanofluids with
time [55,56]. Thermal conductivity readings were measured for the
prepared nanofluids in regular intervals of time at the same
temperatures every time to check the stability of the nanofluids. Here,
the SiO2 nanoparticles were dispersed in the both the
base fluids 60EGW and 40EGW in 0.5% volume concentration. The readings
were taken in a set of three temperatures 25, 30 and
40oC, respectively.
After a gap of seven days the experiment will be repeated for the same
nanofluid at the same temperatures and the readings were noted.
Similarly, the experiments were carried in the same manner for the next
three weeks. On a whole, for the same nanofluid, the thermal
conductivity measurements were taken over period of thirty days at the
same temperatures and the thermal conductivity values were analyzed with
time. The values were observed have less than 1% deviation and are
shown in Figure 5 . Hence, it can be concluded the nanofluid was
stable.
The six samples are shown in Figure 6 are taken on the first
day of preparation and the samples in Figure 7 are taken after
a month gap. The samples were observed to be stabilized as seen with
naked eye. As the other two samples out of eight are base fluids, they
were not shown here.