Thermal conductivity of AlO/water nanofluids (original) (raw)
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Thermal Conductivity of Al 2 O 3 /Water Nanofluids
Nanofluids, fluids with suspended nanoparticles, are of interest as a novel material for improving heat transfer efficiency. The conventional theory of two-component mixtures cannot explain the large enhancement of thermal conductivity of nanofluids. It is to be expected that the thermal conductivity of nanofluids is related with many factors, such as that effect of surfactants, dispersion of particles, convection or Brownian motion of nanoparticles, etc. but the mechanism is not known. Thermal conductivity of Al2O3 nanofluids is studied in this work and compared with that of Fe nanofluids. To study the effect of pH of the base fluid on thermal conductivity, we measured the thermal conductivity of Al2O3 nanofluids with different pH values. Al2O3 nanoparticles were dispersed in water of pH values such as 7.0, 9.65 and 10.94. Nanoparticles have a tendency to form clusters, due to van der Waals interaction resulting in reduction of thermal conductivity. It is understood from the variation of thermal conductivity as the pH value of base fluids varies that the pH of base fluids affects clustering of nanoparticles.
A comparative study of nanofluid (Al2O3) and distilled water in terms of thermal conductivity
International Journal of Chemical Studies
The transfer of heat energy between fluids is frequently used in various processes in industries. The subject of potential heat energy enhancement is great attention in research. With increase in thermal conductivity of fluid, the efficiency of heat transfer in machines can be improved. In this research work, a comparative study is carried out to investigate the effect of Al2O3 Nanofluid on the thermal conductivity with distilled water. KD2 pro thermal property analyzer is used in this work to measure the thermal conductivity. The Al2O3 nanoparticles of the nanofluid have been characterized by using Scanning Electron Microscope, Transmission Electron Microscope, UV-VIS-NIR. Experimentally, it is found that maximum enhancement in thermal conductivity was 8.7% at 80 °C of 0.1 wt % concentration.
Japanese Journal of Applied Physics, 2011
Nanofluids, a mixture of nanoparticles and fluids, have exceptional potential to improve their effective thermal conductivity and thermal diffusivity, aluminum and aluminum oxide nanofluids with five different volume fractions of nanoparticle suspensions in different base fluids, i.e., distilled water, ethylene glycol (EG), and ethanol were prepared by mixing nanopowder and base fluids. Sonication with high-powered pulses was used to ensure the dispersion of nanoparticles in good uniformity in the base fluids. The hot wire-laser beam displacement technique was used to measure thermal conductivity and thermal diffusivity of the prepared nanofluids. The effects of the volume fraction concentration and particle materials on the thermal conductivity and thermal diffusivity of nanofluids were determined. The results showed that the thermal conductivity and thermal diffusivity increased linearly with increasing volume fraction concentration of nanoparticles in the respective base fluids. In addition, the thermal conductivity and thermal diffusivity increased faster in the Al 2 O 3 nanofluids than in all the three base fluids.
Thermal conductivity and specific heat capacity measurements of Al2O3 nanofluids
Journal of Thermal Analysis and Calorimetry, 2012
Thermal conductivities and specific heat capacities of nanoparticles of Al 2 O 3 dispersed in water and ethylene glycol as a function of the particle volume fraction and at temperatures between 298 and 338 K were measured. The steady-state coaxial cylinders method, using a C80D microcalorimeter (Setaram, France) equipped with special calorimetric vessels, was used for the thermal conductivities measurements. The heat capacities were measured with a Micro DSC II microcalorimeter (Setaram, France) with batch cells designed in our laboratory and the ''scanning or continuous method.'' The Hamilton-Crosser model properly accounts for the thermal conductivity of the studied nanofluids. Assuming that the nanoparticles and the base fluid are in thermal equilibrium, the experimental specific heat capacities of nanofluids are correctly justified.
2010
This article reports on the effect of aluminum ͑Al͒ volume fraction concentration on the thermal conductivity and thermal diffusivity of Al nanoparticles suspended in water, ethylene glycol, and ethanol based fluids prepared by the one step method. The Al nanoparticles were independently produced and then mixed with a base fluid to produce the nanoparticles suspension. The thermal conductivity and thermal diffusivity of the nanofluids were measured using the hot wire-laser beam displacement technique. The thermal conductivity and thermal diffusivity were obtained by fitting the experimental data to the numerical data simulated for Al in distilled water, ethylene glycol, and ethanol. The thermal conductivity and thermal diffusivity of the nanofluids increase with an increase in the volume fraction concentration. Physics 81, 074901-1 074901-5 Ali et al. Rev. Sci. Instrum. 81, 074901 ͑2010͒ 074901-6 Ali et al. Rev. Sci. Instrum. 81, 074901 ͑2010͒ 074901-7 Ali et al. Rev. Sci. Instrum. 81, 074901 ͑2010͒ 074901-8 Ali et al. Rev. Sci. Instrum. 81, 074901 ͑2010͒ 074901-9 Ali et al. Rev. Sci. Instrum. 81, 074901 ͑2010͒
The effect of particle size, particle morphology and volume fraction of nanoparticles on the temperature dependent specific heat capacity of metal oxide nanofluids is investigated using differential scanning calorimeter. The stable colloidal suspensions of kerosene based magnetite (Fe3O4), polyalphaolefin (PAO) based alumina (Al2O3) spheres and alumina nanorods are used in the present studies. The nanoparticle concentrations and size of Fe3O4 nanoparticles are varied from 5 to 25 wt% and 3.6 to 8.6 nm, respectively. The results show that the specific heat capacity decreases with increase in volume fraction and particle size in kerosene based Fe3O4 nanofluids but enhances in the case of PAO based Al2O3 nanofluids. These results suggest that PAO molecules strongly modify the interfacial thermal characteristics of Al2O3 nanoparticles that in turn increases the heat capacity of PAO based Al2O3 nanofluids. For kerosene based nanofluids, the Cp data was in reasonable agreement with theoretical model for specific heat, which is derived by assuming thermal equilibrium between the particles and the surrounding fluid (Model II) using classical and statistical mechanics but showed large deviation from the mixing model (Model I). Our study shows that the Cp decreases with increase in the aspect ratio of nanoparticles due to reduced surface atomic contributions. We also compare the effect of particle size and surface morphologies on the thermal conductivity enhancement of nanofluids.
2009
Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1-100 nm suspended in base fluids. In this study, Al 2 O 3 -H 2 O nanofluids were synthesized, their dispersion behaviors and thermal conductivity in water were investigated under different pH values and different sodium dodecylbenzenesulfonate (SDBS) concentration. The sedimentation kinetics was determined by examining the absorbency of particle in solution. The zeta potential and particle size of the particles were measured and the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate attractive and repulsive potentials. The thermal conductivity was measured by a hot disk thermal constants analyser. The results showed that the stability and thermal conductivity enhancements of Al 2 O 3 -H 2 O nanofluids are highly dependent on pH values and different SDBS dispersant concentration of nano-suspensions, with an optimal pH value and SDBS concentration for the best dispersion behavior and the highest thermal conductivity. The absolute value of zeta potential and the absorbency of nano-Al 2 O 3 suspensions with SDBS dispersant are higher at pH 8.0. The calculated DLVO interparticle interaction potentials verified the experimental results of the pH effect on the stability behavior. The Al 2 O 3 -H 2 O nanofluids with an ounce of Al 2 O 3 have noticeably higher thermal conductivity than the base fluid without nanoparticles, for Al 2 O 3 nanoparticles at a weight fraction of 0.0015 (0.15 wt%), thermal conductivity was enhanced by up to 10.1%.
International Nano Letters, 2020
Present work aims to study the dispersion characteristics of Al 2 O 3 nano-dispersoid in water following different periods of ultrasonication and its impact on the thermal conductivity and viscosity of the nanofluid. Nanofluids with 0.5-2 vol% of Al 2 O 3 nanoparticles have been prepared by ultrasonication for varying period. Al 2 O 3 nanofluids reported a maximum thermal conductivity enhancement of 16.1% for 2 vol% of nanoparticle concentration, after an optimum ultrasonication of 2 h beyond which the thermal conductivity decreases with further ultrasonication. The optimum ultrasonication time required for uniform dispersion of nanoparticles increases with the increase in the Al 2 O 3 volume fraction. For 1.5 vol% Al 2 O 3 nanoparticle loading, the viscosity of nanofluid decreased by 33% with an increase in the sonication time from 30 to 90 min. Further increase in sonication time by 30 min resulted in 13% increase in the viscosity of Al 2 O 3 nanofluid. This decrease in the thermal conductivity enhancement and increase in the viscosity beyond the optimum ultrasonication period have been attributed to the re-agglomeration of nanoparticles which are confirmed by TEM, and DLS results carried out after different instants of ultrasonication. The occurrence of re-agglomeration is explained in terms of the convective flow associated with the ultrasonication process. Various theoretical models like Maxwell or Hamilton-Crosser models which when used to predict the thermal conductivity of nanofluid, underestimate the thermal conductivity. A new correlation is, therefore, developed on the basis of experimental results. With an R 2 value of 0.9924, the correlation showed a good agreement with the present thermal conductivity data.
The effect of alumina/water nanofluid particle size on thermal conductivity
Applied Thermal Engineering, 2010
This study examines the effect of particle size, temperature, and weight fraction on the thermal conductivity ratio of alumina(Al 2 O 3 )/water nanofluids. A Al 2 O 3 /water nanofluid produced by the direct synthesis method served as the experimental sample, and nanoparticles, each of a different nominal diameter (20, 50, and 100 nm), were dispersed into four different concentrations (0.5, 1.0, 1.5, and 2.0 wt%). This experiment measured the thermal conductivity of nanofluids with different particle sizes, weight fractions, and working temperatures (10, 30, 50 C). The results showed a correlation between high thermal conductivity ratios and enhanced sensitivity, and small nanoparticle size and higher temperature. This research utilized experimental data to construct a new empirical equation, taking the nanoparticle size, temperature, and lower weight fraction of the nanofluid into consideration. Comparing the regression results with the experimental values, the margin of error was within À3.5% to þ2.7%. The proposed empirical equation showed reasonably good agreement with our experimental results.
International Journal of Heat and Mass Transfer, 2019
The use of hybrid nanofluids has been drawing attention of researchers in order to overcome the drawbacks of mono nanofluid and combine the physical and chemical properties of nanoparticles in a useful way. In the literature, a growing number of researches have been devoted to investigate the thermal performance of hybrid nanofluids. A significant amount of these researches are built on the theoretical correlations for the estimation of thermophysical properties of nanofluids. In the present study, a comparative study is conducted to reveal the influence of theoretical and experimental correlations on the heat transfer performance of hybrid nanofluids. Within this aim, theoretical and experimental based models for predicting thermal conductivity of hybrid nanofluid are evaluated by considering natural convection in a square cavity, which has been studied extensively in the literature. In the study, the natural convection of Al 2 O 3 /water, SiO 2 /water nanofluids and their hybrid combinations are investigated numerically for two different Rayleigh numbers (Ra = 10 4 and 10 5) and three different particle volume fractions (/ = 1, 2 and 3%). The comparative analysis considering the studied parameters was performed in terms of local and mean Nusselt numbers. The results showed that employing theoretical models for thermal conductivity underestimates the heat transfer performance of both mono and hybrid nanofluids. Furthermore, it is surprising that the theoretically calculated SiO 2 /water nanofluid deteriorated the heat transfer performance. It was also observed that hybridizing the nanoparticles could perform the same heat transfer enhancement at a lower particle volume fraction compared to mono nanofluid (Al 2 O 3).