Experimental investigation on effect of ultrasonication duration on colloidal dispersion and thermophysical properties of alumina–water nanofluid (original) (raw)
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Effect of Ultrasonication Duration on Colloidal Structure and Viscosity of Alumina−Water Nanofluid
Industrial & Engineering Chemistry Research, 2014
Nanofluids are promising fluids for heat-transfer applications. Low stability and high viscosity are two important drawbacks for practical applications of nanofluids. The aggregation and sedimentation of nanoparticles are related to the colloidal structure of nanofluids, which directly affects the stability and viscosity. An ultrasonic homogenizer can break the aggregation of particles. The aim of this work was to study the effect of the duration of ultrasonic treatment on colloidal structure, including the stability and temperature-dependent viscosity of a nanofluid. Specifically, a 0.5 vol % Al2O3−water nanofluid was prepared using an ultrasonic homogenizer for various durations from 0 to 180 min. The microstructure, colloid and particle sizes, precipitation, and zeta (ζ) potential were analyzed to investigate the aggregation and sedimentation of the nanofluid. The viscosities of nanofluids subjected to ultrasonic treatment for different durations were also measured at different temperatures from 15 to 45°C. Better particle dispersion, lower particle sizes, smaller colloid sizes, less precipitation, and higher ζ potentials were observed with increasing sonication time. The viscosity of Al2O3−water nanofluid was found to increase with the sonication time up to 60 min and then subsequently decreased. In addition, the viscosity decreased with increasing temperature. The research concluded that more stabler and lower-viscosity nanofluids can be obtained by applying ultrasonic treatment for durations of 90 min or longer.
Effective ultrasonication process for better colloidal dispersion of nanofluid
Ultrasonics Sonochemistry, 2015
Improving dispersion stability of nanofluids through ultrasonication has been shown to be effective. Determining specific conditions of ultrasonication for a certain nanofluid is necessary. For this purpose, nanofluids of varying nanoparticle concentrations were prepared and studied to find out a suitable and rather mono-dispersed concentration (i.e., 0.5 vol.%, determined through transmission electron microscopy (TEM) analyses). This study aims to report applicable ultrasonication conditions for the dispersion of Al 2 O 3 nanoparticles within H 2 O through the two-step production method. The prepared samples were ultrasonicated via an ultrasonic horn for 1 to 5 h at two different amplitudes (25-and 50%). The microstructure, particle size distribution (PSD), and zeta potentials were analyzed to investigate the dispersion characteristics. Better particle dispersion, smaller aggregate sizes, and higher zeta potentials were observed at 3-and 5 h of ultrasonication duration for the 50-and 25% of sonicator power amplitudes, respectively.
2021
Nanofluids (Engineered colloidal suspension of nanoparticles) are the new and promising heat transfer fluids with exceptional properties. Low stability, high pressure drop, and viscosity are the important drawbacks limiting the industrial application of nanofluids. The aggregation and sedimentation of nanoparticles are related to the colloidal structure of nanofluids, which directly affects the stability and viscosity. Various studies revealed that, choosing proper nanoparticle type, size, shape and concentration, base fluid type, operating conditions (pH, temperature, zeta potential, shear, and magnetic field of the solution), ultrasonication probe type, time, power, frequency and intensity, and surfactant type and concentration are the main factors responsible for the nanofluid stability. Among them, ultrasonication treatment is the simplest and most effective technique with longer nanofluid stability period. It is expected that, the present review will provide guidance and contri...
2020
The main goal of this study is to improve the dispersion stability of Al2O3 nanoparticles in polyalphaolefin oil to overcome the sedimentation problem of nanoparticles using the addition of oleic acid as a surfactant. This work investigates the effect of the settling time, temperature, ultrasonic duration and nanoparticles/surfactant (oleic acid) concentration on the dispersion stability of Al2O3 nanoparticles in oil-based solutions. Herein, the visual observation, UV–Vis spectroscopy, dynamic light scattering (DLS) analysis, and transmission electron microscopy (TEM) images were used to evaluate the dispersion stability of the Al2O3 nanoparticles. The results reveal that the thermal method during the synthesis of nanofluids using 50 °C temperature improves the dispersion of nanoparticles. The results also exhibited that increasing the ultrasonic amplitude and prolonging the ultrasonic time during the synthesis of nanofluids influences the dispersion stability. The results showed th...
Achieving homogenised and stable suspensions has been one of the important research topics in nanofluid investigations. Preparing nanofluids, especially from the two-step method, is often accompanied with varying degrees of agglomerations depending on some parameters. These parameters include the physical structure of the nanoparticle, the prevalent particle charge, the strength of van der Waals forces of attraction and repulsiveness strength. Amongst the methods of deagglomeration, the use of ultrasonic vibration is most popular for achieving uniform dispersion. However, there are very few works related to its effect on the thermophysical properties of nanofluids, and above all, standardising the minimum required ultrasonication time/energy for nanofluids synthesis. In this work, the optimum energy required for uniform and initially stable nanofluid has been investigated through experimental study on the combined influence of ultrasonication time/energy, nanoparticle size, volume fraction and temperature on the viscosity of aluminaÀglycerol nanofluids. Three different sizes of alumina nanoparticles were synthesised with glycerol using ultrasonication-assisted two-step approach. The viscosities of the nanofluid samples were measured between temperatures of 20À70 C for volume fractions up to 5%. Based on the present experimental results, the viscosity characteristics of the nanofluid samples were dependent on particle size, volume fraction and working temperature. Using viscometry, the optimum energy density required for preparing homogenous nanofluid was obtained for all particle sizes and volume fractions. Finally, an energy density model was derived using dimensionless analysis based on the consideration of nanoparticle binding/interaction energy in base fluid, particle size, volume fraction, temperature and other base fluid properties. The model's empirical constants were obtained using nonlinear regression based on the present experimental data.
Analysis of the effect of ultrasonic vibration on nanofluid as coolant in engine radiator
Eastern-European Journal of Enterprise Technologies
The paper discusses the combined methods of increasing heat transfer, effects of adding nanofluids and ultrasonic vibration in the radiator using radiator coolant (RC) as a base fluid. The aim of the study is to determine the effect of nanoparticles in fluids (nanofluid) and ultrasonic vibration on the overall heat transfer coefficient in the radiator. Aluminum oxide nanoparticles of 20–50 nm in size produced by Zhejiang Ultrafine powder & Chemical Co, Ltd China were used, and the volume concentration of the nanoparticles varied from 0.25 %, 0.30 % and 0.35 %. By adjusting the fluid flow temperature of the radiator from 60 °C to 80 °C, the fluid flow rate varies from 7 to 11 lpm. The results showed that the addition of nanoparticles and ultrasonic vibration to the radiator coolant increases the overall heat transfer coefficient by 62.7 % at a flow rate of 10 liter per minute and temperature of 80 °C for 0.30 % particles volume concentration compared to pure RC without vibration. The...
Aqueous solution of Al 2 O 3 nanoparticles is dispersed and thermally characterized. Effect of ultrasonic period of action on dispersibility and particle size has been investigated over the concentration of 0.5 vol.% to 1.5 vol.%. Thermal conductivity and convective heat transfer performance of nanoparticle solution have been experimentally studied at different concentrations. Results show the agglomeration of nanoparticles into dilute solution is time dependent and mean diameter of dispersed particle into solution decreases with increasing ultrasonication period. Thermal conductivity linearly increases with increasing the concentration of nanofluids and it was strongly temperature dependent. The enhancement of local convective heat transfer has been achieved about from 27% to 37% by the concentration of 1.5 vol.% of Al 2 O 3 nanofluids where the maximum thermal conductivity was about 5.33% under same concentration.
ScienceDirect, 2016
In the present study, the dynamic viscosity of alumina-engine oil nanofluid in different solid volume fractions and temperatures was experimentally investigated. The nanofluid samples were prepared in the solid volume fractions of 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2% under the temperature range of 5 to 65 °C. The measurements were carried out by CAP 2000+ Viscometer, supplied by Brookfield of the USA. Using the experimental data, new correlations for predicting the dynamic viscosity of alumina-engine oil at different temperatures were proposed. The experiment results at different shear rates showed that all nanofluid samples exhibit the Newtonian behavior. The results also revealed that the viscosity of the nanofluid increases with the solid volume fraction. Moreover, it has been found that with increasing temperature, the viscosity of nanofluids decreases, and it was more tangible at the lower temperatures. The comparison between experimental findings and theoretical models showed that these models failed to predict the correct values of the viscosity of the nanofluids at all solid volume fractions. The experimental data also indicated that the maximum viscosity enhancement of nanofluid was 132% compared with that of base fluid.
Viscosity of alumina nanoparticles dispersed in car engine coolant
Experimental Thermal and Fluid Science, 2010
The present paper, describes our experimental results on the viscosity of the nanofluid prepared by dispersing alumina nanoparticles (<50 nm) in commercial car coolant. The nanofluid prepared with calculated amount of oleic acid (surfactant) was tested to be stable for more than 80 days. The viscosity of the nanofluids is measured both as a function of alumina volume fraction and temperature between 10 and 50°C. While the pure base fluid display Newtonian behavior over the measured temperature, it transforms to a non-Newtonian fluid with addition of a small amount of alumina nanoparticles. Our results show that viscosity of the nanofluid increases with increasing nanoparticle concentration and decreases with increase in temperature. Most of the frequently used classical models severely under predict the measured viscosity. Volume fraction dependence of the nanofluid viscosity, however, is predicted fairly well on the basis of a recently reported theoretical model for nanofluids that takes into account the effect of Brownian motion of nanoparticles in the nanofluid. The temperature dependence of the viscosity of engine coolant based alumina nanofluids obeys the empirical correlation of the type: log (l nf ) = A exp(BT), proposed earlier by Namburu et al.
Influence of Sonication on the Stability and Thermal Properties of Al 2 O 3 Nanofluids
Nanofluids containing Al 2 O 3 nanoparticles (either 11 or 30 nm in size) dispersed in distilled water at low concentrations (0.125-0.5 wt%) were prepared using two different ultrasonic devices (a probe and a bath sonicator) as the dispersant. The effect of the ultrasonic system on the stability and thermal diffusivity of the nanofluids was investigated. Thermal diffusivity measurements were conducted using a photopyroelectric technique. The dispersion characteristics and morphology of the nanoparticles, as well as the optical absorption properties of the nanofluids, were studied using photon cross correlation spectroscopy with a Nanophox analyzer, transmission electron microscopy, and ultraviolet-visible spectroscopy. At higher particle concentration, there was greater enhancement of the thermal diffusivity of the nanofluids resulting from sonication. Moreover, greater stability and enhancement of thermal diffusivity were obtained by sonicating the nanofluids with the higher power probe sonicator prior to measurement.