Figure 6 Viscosity versus concentration at various temperatures and constant shear rates. In order to determine the rheological behaviors this website of GNP nanofluids, the viscosity of aqueous GNPs versus shear rate was measured

at the temperature range of 20°C to 60°C, and the results are shown in Figure 7. The viscosity of distilled water decreases exponentially as a function of shear rate which indicates its shear thinning (pseudoplastic) behavior. Following the trend of water, the samples of GNP nanofluid also exhibit the shear thinning property. The cause of this non-Newtonian shear thinning can be explained generally as follows. At low shear rates, as the spindle rotates in the fluid, the structure of the fluid molecules changes temporarily and gradually aligns themselves in the direction of increasing shear; it produces less resistance and hence a reduction in viscosity. When the shear rate is high enough,

the maximum amount of possible shear ordering is attained, and the aggregates are broken down to smaller sizes, decreasing the friction and hence the viscosity [30]. If we increase the shear rate further, it will not make any alteration on the viscosity. Due to small size and large surface area of the nanoparticle, there is a possibility for structuring at low shear rates and a deformation and restructuring www.selleckchem.com/products/BAY-73-4506.html at high shear rates. Hence, nanofluid also follows the same trend. It is observed at all temperatures that the shear Fluorouracil thinning property is more pronounced at higher concentrations. This points out that at low concentrations, the nature of base fluid plays a major role in shear thinning, but at higher concentrations, there is a significant contribution from the interaction between the nanoparticle and fluid. Figure 7 Plots of viscosity versus shear rate at various concentrations and temperatures. The results indicate that prepared nanofluids are suitable to use at elevated temperatures. By increasing the temperature, thermal movement of molecules and Brownian motion intensify and intramolecular interactions

become weakened. In addition, rheological test on nanofluids revealed that higher concentration increases the viscosity; however, other investigated parameters such as temperature and specific surface areas have an important influence on the viscosity behavior of nanofluids. Thermal conductivity The development of high-performance thermal systems has increased the interest on heat transfer enhancement techniques where heat transfer fluids play an important role in developing efficient heat transfer equipment. Thermal conductivity measurements in this work were done based on the THW method, and the analyzer device has a 5% accuracy over 5°C to 40°C temperature range. In the present study, the calibration tests for distilled water was verified by previous data [5, 17, 31], and the results are obtained within 2% to 4% accuracy as demonstrated in Figure 8.