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.