## 2 Nanofluid Thermal Conductivity
### Effects of Temperature on Nanofluid Thermal Conductivity
[28] studied the thermal conductivities of Al\({}_{2}\)O\({}_{3}\)-Ethylene Glycol, Cu-water, and Al-transformer oil nanofluids. It was observed that the thermal conductivity increased with temperature. It was suggested that this increase was a result of increased Brownian motion at higher temperatures. It was also noted that the contribution of microconvection to heat transfer increases with the increase of Brownian motion, which also leads to enhanced thermal conductivity. [PERSON] et al. [28] studied the thermal conductivities of Al\({}_{2}\)O\({}_{3}\)-Ethylene Glycol, Cu-water, and Al-transformer oil nanofluids. It was observed that the thermal conductivity increased with temperature. It was suggested that this increase was a result of increased Brownian motion at higher temperatures. It was also noted that the contribution of microconvection to heat transfer increases with the increase of Brownian motion, which also leads to enhanced thermal conductivity. [PERSON] et al. [28] studied the thermal conductivities of Al\({}_{2}\)O\({}_{3}\)-Ethylene Glycol, Cu-water, and Al-transformer oil nanofluids. It was observed that this increase was a result of increased Brownian motion at higher temperatures. It was suggested that this increase was a result of increased Brownian motion at higher temperatures. It was also noted that the contribution of microconvection to heat transfer increases with the increase of Brownian motion, which also leads to enhanced thermal conductivity. temperatures. Also, using the transient line heat source method, [PERSON] et al. [10] measured the thermal conductivities of CuO-water, CuO-Ethylene Glycol, and CuO-engine oil nanofluids as a function of temperature. The results showed an increase in thermal conductivity with temperature for each nanofluid tested. It was suggested that this increase was caused by increased Brownian motion at higher temperatures. However, several researchers have suggested that the effect of temperature on the thermal conductivity of nanofluids is solely a result of the increase in thermal conductivity of the base liquid [15; 26; 42]. Using the transient short hot-wire method, [PERSON] et al. [15] measured the thermal conductivities of AIN-Ethylene Glycol and AIN-propylene glycol nanofluids within the temperature range on 10-60 \({}^{\circ}\)C. A negligible change in thermal conductivity with the increase of temperature was observed. At a given temperature, the thermal conductivity of the nanofluid was almost identical to that of the base fluid. Additionally, [PERSON] et al. [26] observed that the thermal conductivity of MgO-Ethylene Glycol nanofluid increased slightly with temperature. However, the thermal conductivity enhancement ratio remained almost constant. It was suggested that the change in thermal conductivity of nanofluids with temperature follows the trend of increase in the thermal conductivity of their respective base fluid. Also, [PERSON] et al. [42] measured the thermal conductivity of Al\({}_{2}\)O\({}_{3}\)-glycerol nanofluid as a function of temperature. The thermal conductivity did not vary significantly with temperature, and followed the pattern of the base fluid, glycerol. It was suggested that the effect of temperature on the thermal conductivity of nanofluids is dependent on the characteristics of the nanofluid. [PERSON] et al. [23] measured the thermal conductivity of Ag-Ethylene Glycol, Ag-hexane, and Ag-water nanofluids as a function of temperature. The thermal conductivity of Ag-Hexane nanofluid decreased with temperature. The thermal conductivity of Ag-water nanofluid increased with temperature at lower concentrations, but decreased with the increase of temperature at higher concentrations. It was suggested that this change in the behavior of water-based nanofluid at higher temperatures was related to the presence of Gum Arabic surfactant. Water generally does not transfer energy between molecules, but rather the energy is stored within hydrogen bonds in large clusters of molecules that occur at lower temperatures [23].