Synthesis of Aqueous and Nonaqueous Iron Oxide Nanofluids and Study of Temperature Dependence on Thermal Conductivity and Viscosity

Abstract

We investigate the temperature-dependent thermal conductivity (k) of aqueous and nonaqueous stable nanofluids with average particles size of 8 nm stabilized with a monolayer of surfactant. Iron oxide (Fe3O4) nanoparticles are synthesized by a coprecipitation technique and are characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), dynamic light scattering (DLS), and theromogravimetric analysis (TGA). The particles are functionalized with suitable surfactants and dispersed in aqueous and nonaqueous base fluids. The thermal conductivity and viscosity measurements are carried out using a transient hot wire and a rotational rheometer, respectively. The thermal conductivity of aqueous nanofluids increases with temperature while it shows a decrease in nonaqueous nanofluids. Interestingly, the ratio of thermal conductivity of both nanofluids with respect to base fluids (k/k f) remains constant with an increase in temperature, irrespective of the nature of the base fluid. This observation is in sharp contrast to microconvection theory predictions of an increase in thermal conductivity with a rise in temperature. These results unambiguously confirm the less dominant role of microconvection on thermal conductivity enhancement. Although the viscosity of nanofluids decreases with increases in temperature, the viscosity ratio with respect to base fluid remains constant. These results show that the viscosity and thermal conductivity of nanofluids simply tracks those properties of the base fluids. Measurement of particle size with temperature shows that the average particle size remains constant with temperature.

The effect of functionalized silver nanoparticles over the thermal conductivity of base fluids

“…Previous works involving enhanced thermal conductivity of water usually comprises addition of CuO, [20][21][22] Al 2 O 3 6,22-24 and iron oxide 25,26 to water and all agreed on enhancement in thermal conductivity upon addition of NPs.…”

Deterioration in effective thermal conductivity of aqueous magnetic nanofluids

“…13 It was also shown that at the same volume fractions, Fe 3 O 4 nanofluids have higher thermal conductivity than other metal oxide nanofluids such as CuO, TiO 2 , and Al 2 O 3 as a result of nanoparticle alignment. 26 Although the thermal conductivity of aqueous nanofluids increases, while that of non-aqueous nanofluids decreases with temperature, the ratio of the nanofluid thermal conductivity to base fluid thermal conductivity remains constant, 25,27 implying that the temperature dependency of thermal conductivity does not change upon addition of nanoparticles. This enhancement in thermal conductivity was found to be higher 19,26 than predictions by the effective medium theory (EMT) proposed by Maxwell 28 and other theoretical models.…”

“…Similarly, Shima et al reported an enhancement in thermal conductivity of water-based magnetic nanofluids having the same tetramethyl ammonium hydroxide layer stabilizing the particles. 27 On the other hand, Wang et al 34 showed an enhancement in thermal conductivity for oleic acid coated magnetite particles dispersed in toluene. The same particles dispersed in water after ligand exchange with poly(acrylic acid) showed a fluctuating trend for the thermal conductivity change as a function of particle concentration, which was attributed to the aggregation of particles leading to an increase in interfacial thermal resistance.…”

Near-Field Nanofluid Concentration Measurement by Rayleigh Particle Scattering Bragg Grating Evanescent Wave

“…Nanometer-sized stable metal, metal oxides or carbon particles in various forms could be suspended in the industrial heat transfer fluids (water and organic liquids), and can result in anomalously large enhancements of the thermal conductivities. [1][2][3][4][5] These reports show that only 5 vol. % of nanoparticles such as alumina (Al 2 O 3 ), copper oxide (CuO), and copper (Cu) dispersed in different base fluids, the thermal conductivity of the nanofluids was observed a significant improvement ($60%) as compared to the corresponding base fluids.…”