Experimental Study on the Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids

Abstract

This paper reports measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al 2 O 3 thin film. Using distilled water and toluene as standard liquids of known thermal conductivity and thermal diffusivity, the length and radius of the hot wire and the thickness of the Al 2 O 3 film are calibrated before and after application of the coating. The electrical leakage of the short-hot-wire probes is frequently checked, and only those probes that are coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Al 2 O 3 /water, ZrO 2 /water, TiO 2 /water, and CuO/water nanofluids are measured and the effects of the volume fractions and thermal conductivities of nanoparticles and temperature are clarified. The average diameters of Al 2 O 3 , ZrO 2 , TiO 2 , and CuO particles are 20, 20, 40, and 33 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancement and can be predicted accurately by the model equation of Hamilton and Crosser, when the spherical nanoparticles are dispersed into fluids.

Thermal Conductivity and Viscosity Measurements of Water-Based TiO2 Nanofluids

“…Contrary to this result, Das et al [7] observed a two-to-four fold increase in the thermal conductivity of nanofluids, containing Al 2 O 3 and CuO nanoparticles in water, over a temperature range of 21 • C to 51 • C. Several groups [8][9][10][11][12][13][14] reported studies with different nanofluids, which support the result of Das et al [7]. For the temperature dependence of the relative thermal conductivity (ratio of effective thermal conductivity of nanofluids to thermal conductivity of base fluid), although a major group of publications showed an increase with respect to temperature, some of the other groups observed a moderate enhancement or temperature independence [6,[15][16][17][18].…”

Heat transfer in nanoparticle suspensions: Modeling the thermal conductivity of nanofluids

“…An early study by Eastman et al 31 reported that an aqueous nanofluid containing 5% (v/ v) copper oxide nanoparticles exhibited a thermal conductivity that was 60% greater than that of water, and another aqueous nanofluid containing 5% (v/v) alumina nanoparticles exhibited a thermal conductivity that was 40% greater than that of water. More recent studies, however, have reported more modest enhancements [32][33][34][35] in similar nanofluids. It should also be added here that differences in reported values of the enhancement are quite common in the nanofluid literature.…”

Characteristic analysis of De-Ionised water and Ethylene Glycol based Aluminium Oxide Nanofluid

“…Spherical type nanoparticle of 4.2% volume fraction produced 15.8% thermal conductivity enhancement where for 60nm cylindrical nanoparticle exhibits 23% enhancement. The result obtained [34] was compared with Hamilton-Crosser [29] model, which showed the good relationship. For TiO2 and di water nanofluid, the spherical shape produced only 29.7% and 33%, for cylindrical type nanoparticles of same volume fraction.…”

“…As per the parameter comparison, the particle volume fraction dependence on thermal conductivity is higher than temperature dependence. Some other research works were also carried out by researcher [33][34][35][36].…”