Suspensions Of Alumina Nanoparticles Research Articles

Experimental investigation of isobaric heat capacity and viscosity for suspensions of alumina nanoparticles in [C4mim][BF4] ionic liquid

Experimental investigation of isobaric heat capacity and viscosity for suspensions of alumina nanoparticles in [C4mim][BF4] ionic liquid

AGLOMERATION OF Al2O3 NANOMETRIC AND SUBMICROMETRIC PARTICLES BY SPRAY DRYING FOR THEIR USE AS FEEDSTOCK IN THERMAL SPRAYING COATINGS

This study focuses on optimizing the parameters of the spray-drying process for the agglomeration of both nanometric and submicrometric Al2O3 particles for their use as feedstock to manufacture thermally sprayed coatings. Initially, for an aqueous suspension with submicrometric alumina particles, d10 = 0.8 to d90 = 2.0 µm, named SA, was evaluated the effect of: i) The solids percentage in the aqueous suspension, ii) the feed flow rate and iii) the hot air rate used to evaporate the water in the suspension, on the agglomeration efficiency and the morphology of agglomerated obtained, utilizing a factorial experimental design with three factors and two levels. The agglomeration efficiency was calculated as the ratio between the weight percentage of granulated particles and the weight of solids in the sprayed slurry, while the morphology was analyzed by scanning electron spectroscopy SEM. The agglomeration results for the SA suspension indicate that the highest efficiency was achieved with a solid percentage in an aqueous suspension of 30 wt. % (10 vol.%), a feed rate of 3.1 ml/min and a hot air rate of 5.5 m3/min at a temperature of 220 °C, obtaining spherical agglomerates. Nevertheless, different morphologies of agglomerate were obtained based on the others experimental runs, such as hollow spheres. Subsequently, these parameters were replicated for a suspension of alumina nanoparticles, d50=80 nm, called NA, to obtain granules with a spherical morphology, composed of primary and secondary agglomerates whose size distributions correspond to d10 = 5 to d90 = 11 µm and d10 = 30 to d90 = 44 µm, respectively, with a total granulation efficiency of 80%, of which, 90% have a suitable range size to be used as raw material in the production of coatings by means of thermal spraying.

Effects of Branched Fins on Alumina and N-Octadecane Melting Performance Inside Energy Storage System

The importance of Phase change material (PCM) energy storage systems is no longer new in the industry. However, the influence of using branched fins inside the energy storage system on the melting process of alumina nanoparticles and n-octadecane has not been reported in the literature. Consequently, the outcome of a study on the numerical simulation for optimizing the melting performance of a PCM in various tubes, including those with branching fins is presented in this report. Four examples were assessed in relation to a suspension of alumina nanoparticles and n-octadecane paraffin that contains heated fins. A numerical technique based on the Galerkin finite element method (GFEM) was used to solve the dimensionless governing system. The average liquid percentage over the flow zone in question was computed. The primary results indicated that altering the number of heated fins might affect the flow structures, the system’s irreversibility, and the melting process. Case four, with eight heated fins, likewise produces the greatest average liquid fraction values and completes the melting process in 850s. Additionally, when 6% nano-enhanced PCM was used instead of pure PCM, the melting process is accelerated by 28.57 percent.

Study on the novel suppression of heat transfer deterioration of supercritical water flowing in vertical tube through the suspension of alumina nanoparticles

One of the novel strategies of improving the heat transfer characteristics of heat exchanger systems is the application of nanofluids as the heat transfer media. The purpose of the current study is to evaluate the effectiveness of utilizing the suspension of nanoparticles in water at supercritical pressures in the mitigation of heat transfer deterioration (HTD), an adverse phenomenon in supercritical fluids heat exchanger systems. The thermohydraulic performances of the supercritical water-based nanofluids are analysed using the dimensionless parameters based on normalized Nusselt numbers and Fanning friction factors, Nunf/Nubf, fnf/fbf and PEC = (Nunf/Nubf)/(fnf/fbf)1/3. The results reveal that the suspension of Al2O3 nanoparticles increase the mitigation of HTD, with 1.5% of Al2O3 nanoparticles volume fraction achieving up to 20.22% suppression of wall temperature peaks. In accordance with the Reynold’s analogy, the results show a positive correlation between heat transfer performance and pressure loss. Furthermore, the effect of nanoparticles on buoyancy flow are investigated based on Jackson's buoyancy criterion (Gr/Re2.7). It is obtained that (Gr/Re2.7) decreases at the pseudo-critical region as the nanoparticles volume fraction increases because the increase in the volume fraction leads to the reduction in difference between the bulk and near-wall fluid densities, thus leading to weakening of buoyancy flow and subsequent mitigation of HTD. Also, the increasing nanoparticles volume fraction causes the reduction of kinematic viscosity but enhances the velocity and turbulent kinetic energy close to the wall, which also, contributes to the mitigation of HTD.

Viscosity and isobaric specific heat capacity of alumina nanoparticle enhanced ionic liquids: An experimental approach

Temperature and loading dependences on the rheological behavior and isobaric specific heat capacity of several suspensions of alumina nanoparticles in a binary mixture of [C2mim][CH3SO3] ionic liquid and water were experimentally determined to assess its potential condition of enhanced heat transfer fluids. Rheological tests show a clear Newtonian behavior for the base fluid and the NEILs with lower Al2O3 concentrations while higher amounts of alumina nanoparticles entail non-Newtonian fluids and increase in viscosity up to 78%. The heating-cooling viscosity tests reveal that no significant viscosity hysteresis occur and VFT equation adequately describe the temperature dependence. Isobaric specific heat capacities decrease (<10%) with nanoparticle mass fraction and increase (<10%) with temperature. The goodness of the Raud et al. correlation for predicting the isobaric specific heat capacity of nanoparticles enhanced fluids is discussed.

Stability appraisement of the alumina-brine nanofluid in the presence of ionic and non-ionic disparents on the alumina nanoparticles surface as heat transfer fluids: Quantum mechanical study and Taguchi-optimized experimental analysis

Nanofluids stability is a key factor that influences the properties of nanofluids, and it is necessary to study and analyze the influential factors affecting the dispersion stability of nanofluids. Although numerous methods have been developed to evaluate the stability of nanofluids, stability assessment through quantum mechanical study has been largely overlooked and theoretical behaviors behind this enhancement remain to be elucidated. The present work focuses on achieving stabilization of Al2O3/brine nanofluids by adding three surfactants, including Sodium Dodecyl Sulfate (SDS), Triton X-100(TRI), and Cetyl pyridinium chloride (CPC) into the suspension of alumina nanoparticles, which surrounds nanoparticles through the particle surface. Quantum mechanical calculations performed to understand the stability conferred by the surfactants on the surface and heat transfer capability studied using Taguchi-optimized experimental analysis. An experimental investigation to quantify the combined effect of pH, volume fraction, sodium chloride concentration, and temperature, on the dispersion and thermal conductivity of Al2O3/brine nanofluid, revealed that the optimum value for the thermal conductivity is obtained mainly by controlling all parameters as well as surfactant type. The SDS and TRI surfactants on the surface of the alumina nanoparticles (NP) increased the particle dispersion and heat transfer as chain-like nanofluids, while the CPC enhanced the particle aggregation and formed flake-like nanofluids to form nanofluids with lower thermal conductivity. The DFT calculations revealed that the interaction energy between NP and SDS molecules was stronger over other surfactants. Further, NP/SDS system was the most stable configuration and had the most negative binding energy. The QTAIM analysis indicated that hydrogen bridge interactions favor the stability of the fluid-surfactant mixture as NP/SDS > NP/TRI > NP/CPC.

Creation of nanoparticles and surface nanostructures of alumina by hot water treatment

In this report, we present a detailed study of the formation of alumina nanostructures at the surface of aluminium plate by hot water treatment (HWT) at various temperatures. The nanostructures were studied by scanning electron microscopy. The superhydrophilic property of the treated surface was revealed and its stability was investigated. It was shown that HWT could be used also for synthesis of the aqueous suspensions of alumina nanoparticles. It is proposed that the method can be applied for production of surface nanostructures and nanoparticles of various metal oxides.

The Study of Gum Arabic as Surfactant on the Stability of Water-based Alumina Nanoparticle Suspensions

The stability study of alumina nanoparticle suspensions has been investigated by using gum arabic as a surfactant. The effect of particle volume fraction of alumina nanoparticle and gum arabic concentration were observed. The stability of the suspension was characterized using zeta potential and particle size distribution analysis. Several volume fractions of alumina and gum arabic concentration were dispersed in water as a solvent for suspension stability. The result showed that the stability of water-based alumina nanoparticle suspensions was increase with the decreasing of particle volume fraction and increasing of gum arabic concentration. The particle size distribution was narrow with decreasing particle volume fraction and increasing gum arabic concentration. The hydrodynamic diameter of the particles was smaller with the increasing of gum arabic concentration. The smallest particle size recorded was 164.6 nm at 0.5% gum arabic concentration. Zeta potential values were increased with the increasing of gum arabic concentration. The highest zeta potential was recorded at -36.0 mV. It can be concluded that gum arabic can be used for stabilization of water-based alumina nanoparticle suspensions.

Enhanced thermal conductivity of alumina nanoparticle suspensions by femtosecond laser irradiation

This work reports significant enhancements over the Hashin-Shtrikman upper bound, by means of femtosecond laser irradiation, of thermal conductivity of alumina nanoparticle suspensions dispersed in water. By adjusting laser parameters, the applied femtosecond laser irradiation could enhance the colloidal stability of the suspension and reduce the size of nanoparticles. The thermal conductivity and zeta potential of the suspensions were measured before and after the laser-induced stabilization and fragmentation processes. When the laser stabilization and laser fragmentation processes were combined, the thermal conductivity of the suspension increased up to about 40% compared to the thermal conductivity of the base fluid at 1wt%. This laser technique demonstrates a strong potential to produce nanofluids with high thermal conductivity and colloidal stability.

Role of molecular structure of monosaccharides on the viscosity of aqueous nanometric alumina suspensions

The effect of molecular structure of d-galactose, d-mannose, d-glucose, 2-deoxy-d-glucose and 3-O-methyl-d-glucose on the viscosity of aqueous alumina nanoparticle suspensions was investigated by rheological measurements. The viscosity was found to be dependant on the molecular structure of these hexopyranoses. The research reveals that the orientation of primary and quaternary hydroxyl groups in a pyranose ring plays a crucial role in dispersing properties of monosaccharides. Moreover, the most important is the mutual orientation of these hydroxyl groups. Monosaccharides with axial and equatorial orientation of hydroxyl groups at first (C1) and fourth (C4) carbon atom in pyranose ring decrease the viscosity more than monosaccharides with two axial hydroxyl groups in these positions. Due to the differences in molecular structure of saccharides resulting in different shape of molecules and different compatibility to the water structure, the saccharides differ in ability to disturb water layers around alumina particles.

Combined Effects of Slip Motion and Boundary Conditions on Enhanced Heat Transfer in Natural Convection Flows of Enclosed Nanofluids

The experimental studies dealing with natural convection of nanofluids in differentially heated enclosures demonstrate that the addition of nanoparticles to a pure base liquid is substantially detrimental, which can be ascribed to the formation of two stagnant fluid layers near the top and bottom adiabatic walls. Thus, if the horizontal walls are differentially heated instead of being perfectly insulated, the consequent development of a pair of concentration boundary layers near them may possibly imply a heat transfer enhancement. In this connection, a two-phase mixture model is employed to perform a numerical study of laminar natural convection in a square cavity containing water suspensions of alumina nanoparticles with a diameter of 33 nm and an average volume fraction in the range 0.001–0.04, assuming that Brownian diffusion and thermophoresis are the primary slip mechanisms between solid and liquid phases. The cavity is differentially heated at sides, whereas the horizontal walls are assumed to be either adiabatic or one heated and the other cooled, with a Rayleigh number in the range 4 × 105–3 × 106. It is found that the heating-from-below configuration is featured by periodic heat transfer, with a rate remarkably higher than that typical of the pure base liquid.

Enhancement of stability of aqueous suspension of alumina nanoparticles by femtosecond laser irradiation

In this work, we report substantially enhanced colloidal stability of aqueous nanoparticle suspensions by ultrashort laser pulse irradiation. A Ti:Sapphire femtosecond laser (wavelength: 800 nm; pulse duration: 50 fs at full width at half maximum) was used to modify the electrochemical properties of nanoparticle suspensions at laser fluences below the particle ablation threshold. The colloidal stability of the suspension was evaluated by zeta potential and dynamic light scattering (DLS). The DLS results along with the images from transmission electron microscopy revealed that the laser irradiation caused no distinct morphological change to the individual alumina particles, but a substantial portion of the clustered particles was fragmented by the laser pulses, decreasing the apparent size of the suspended particles. Also, X-ray photoelectron spectroscopy analysis indicates that the laser irradiation modified the surface chemistry of the alumina particles. The stabilizing capability of the proposed technique was turned out to be better than that of conventional ultrasonic treatments. The stability of the laser-treated sample with no added surfactant was maintained for up to 30 days, without requiring an additional homogenizing process such as magnetic stirring.

Correlations of heat transfer effectiveness in a minichannel heat sink with water-based suspensions of Al2O3 nanoparticles and/or MEPCM particles

In this work, an experimental study is carried out to examine the cooling performance of a minichannel heat sink using water-based suspensions of alumina nanoparticles (nanofluid), and/or microencapsulated phase change material (MEPCM) particles in terms of the averaged Nusselt number Nu¯itd, the wall temperature control effectiveness εTw, and the averaged thermal resistance control effectiveness εRavg for the relevant parameters in the following ranges: the Reynolds number, Re=133–1515; the mass fractions of the nanoparticles and/or MEPCM particles dispersed in the water-based suspensions, ωnp or ωmepcm=0–10wt.%; and the heating power. The heat sink was fabricated from copper with 10 rectangular minichannels which were maintained at a uniform base heat flux. The resulting experimental data for the various effectivenesses of using the water-based suspensions formulated in the minichannel sink were found well correlated with the relevant dimensionless parameters in general forms.

Experiment on thermal performance of water-based suspensions of Al2O3 nanoparticles and MEPCM particles in a minichannel heat sink

In the present study, experimental efforts have been performed to explore the forced convection heat transfer efficacy of using water-based suspensions of alumina nanoparticles (nanofluid) and microencapsulated phase change material (MEPCM) particles (PCM suspension) to replace the pure water as the working fluids in a minichannel heat sink (Mini-CHS). The heat sink fabricated from copper consists of 10 rectangular minichannels, each of which has a width of 1mm, a depth of 1.5mm, a length of 50mm, having a hydraulic diameter of 1.2mm. The minichannel heat sink was heated with a uniform base heat flux with the Reynolds numbers ranged from 133 to 1515. The mass fractions of the nanoparticles and MEPCM particles dispersed in the water-based suspensions were in the ranges of 2–10wt%, respectively. Experimental results obtained reveal that the heat dissipation effectiveness of the nanofluid and PCM suspension depends significantly on their flow rates through the heat sink. For the nanofluid, the highest enhancement of 57% in the averaged heat transfer coefficient was detected under the highest flow rate; while for the PCM suspension, the highest enhancement of 51% under the lowest flow rate. For the hybrid water-based suspensions, the effect of simultaneous dispersion of the nanoparticles and MEPCM particles in water appears to be supplementary with added benefit of simultaneous increases in the effective thermal conductivity and specific heat such that the heat transfer effectiveness could be further increased up to 56% with little dependence on the flow rate.

Shear thinning behavior of aqueous alumina nanoparticle suspensions with saccharides

Concentrated aqueous alumina nanoparticle suspensions with addition of low molecular weight saccharides such as fructose, glucose, sucrose, and others were studied by rheometry and low temperature differential scanning calorimetry. The viscosity of the suspensions and melting behaviors of the frozen suspensions were used to develop a model based on particle clustering which describes the viscosity decrease seen with the addition of these saccharides. It appears that characteristics of particle clustering are dependent on the saccharide type and concentration. The proposed model is in qualitative agreement with the observed behavior and the model proposed earlier based on bound water.

Preparation of alumina nanoparticle suspensions with narrow particle size distribution

Dynamic light scattering (DLS) was applied to the study of the process of the preparing deaggregated water suspensions of alumina nanopowders with specific surface areas of 20–140 m2/g. Nanopowders were prepared by the electric explosion of wire and laser evaporation and, according to electron microscopy (TEM), consisted of nonagglomerated spherical nanoparticles with lognormal size distribution. According to DLS, nonsedimenting water suspensions of alumina nanoparticles, stabilized by sodium citrate at a 5 mM concentration, contain substantial fraction of aggregates. The dynamics of the change in the mean average size of aggregates under exhaustive ultrasound treatment of suspensions with 10 g/l concentration for 1.5–4 h by two types of ultrasonic processors was studied. It was shown that the mean average size of aggregates exponentially diminishes by 1.5–2 times and the fraction of individual particles in suspension enlarges from 45 to 85%. Sequentially centrifuging the suspension at 18000 g separates the remaining aggregates and results in suspensions of individual alumina nanoparticles. Particle size distributions in these suspensions obtained by TEM and DLS are the same within experimental error.

Regularities of ultrasonography of suspensions of alumina nanoparticles in biological media

This paper studies the echo-contrast properties of an alumina nanopowder suspension using ultrasonography (US) fully corresponding in its characteristics to the techniques of medical ultrasound diagnostics of organs and tissues. The purpose of this study was to search for the possible effect of the ionic and protein composition of the biological medium on the intensity of the reflected echo signal of the contrast material based on nanoparticles. It was found that the pH of the blood promotes the maximum use of echo contrast options of alumina nanopowder suspensions. Particle size measurements in the suspension using the dynamic light scattering technique showed the stabilizing effect of blood serum and plasma on the nanopowder suspension, resulting in the attenuation of the echo signal. The data offer a basis for the development of new contrast materials based on nanoparticles for the ultrasound imaging of the heart and blood vessels. The considered mechanisms of the established phenomena make it possible to elucidate the processes of interaction of metal oxide nanoparticles with biological molecules.

Elucidation of Viscosity Reduction Mechanism of Nano Alumina Suspensions with Fructose Addition by DSC

Control of the rheological properties of the nanoparticle suspensions is challenging. In this study influence of the solids content and the fructose addition on the viscosity of nano alumina suspensions have been investigated by low temperature differential scanning calorimetry (LT‐DSC), rheometry, and zeta potential measurements. Analysis of the water melting events in LT‐DSC revealed useful information for explaining the rheological behavior of the nanoparticle suspensions. It was shown that the bound water layer has a negligible effect on the viscosity of micrometer‐size particle suspension while it increases the effective solid content of alumina nanoparticle suspensions significantly leading to high viscosities. The presence of fructose modifies the bound water layer, decreases the effective solids content, hence resulting in viscosity reduction. Fructose addition lowers the pH of the suspension, but has a negligible effect on the zeta potential. The origin of the bound water, and electrostatic and steric effects of the fructose addition on the viscosity are discussed.

Suspended nanoparticles in surfactant media as a microextraction technique for simultaneous separation and preconcentration of cobalt, nickel and copper ions for electrothermal atomic absorption spectrometry determination

The aim of this study was to describe a new method of microextraction based on the suspension of alumina nanoparticles in the surfactant media for simultaneous separation and preconcentration of the ultra-traces of cobalt, nickel and copper ions. In this technique, the alumina nanoparticles were suspended in the non-ionic surfactant solution of Triton X-114. The analytes in the sample solution were adsorbed onto the nanoparticles. After the phase separation based on the cloud point of the mixture at 40°C, the nanoparticles settled down in the surfactant rich phase. Then 120μL of nitric acid (3.0molL−1) was added to the surfactant rich phase which caused desorption of the analytes. Finally, the liquid phase was separated by centrifugation from the nanoparticles and was used for the quantification of the analytes by the electrothermal atomic absorption spectrometry (ETAAS). The parameters affecting the extraction and detection processes were optimized. Under the optimized experimental conditions (i.e. pH∼8, Triton X-114, 0.05% (v/v); temperature 40°C), a sample volume of 25mL resulted in the enhancement factors of 198, 205 and 206 and detection limits (defined as 3Sb/m) of 2.5, 2.8 and 2.6ngL−1 for Co(II), Ni(II) and Cu(II) respectively. The sorbent showed high capacity for these metal ions (30–40mgg−1 sorbent). The method was successfully applied to the determination of the analytes in natural water samples.

Aggregation and settling in aqueous polydisperse alumina nanoparticle suspensions

Nanoparticle suspensions (also called nanofluids) are often polydisperse and tend to settle with time. Settling kinetics in these systems are known to be complex and hence challenging to understand. In this work, polydisperse spherical alumina (Al2O3) nanoparticles in the size range of ~10-100nm were dispersed in water and examined for aggregation and settling behaviour near its isoelectric point (IEP). A series of settling experiments were conducted and the results were analysed by photography and by Small Angle X-ray Scattering (SAXS). The settling curve obtained from standard bed height measurement experiments indicated two different types of behaviour, both of which were also seen in the SAXS data. But the SAXS data were remarkably able to pick out the rapid settling regime as a result of the high temporal resolution (10s) used. By monitoring the SAXS intensity, it was further possible to record the particle aggregation process for the first time. Optical microscopy images were produced on drying and dried droplets extracted from the suspension at various times. Dried deposits showed the rapid decrease in the number of very large particles with time which qualitatively validates the SAXS prediction, and therefore its suitability as a tool to study unstable polydisperse colloids. Keywords: Nanoparticles, nanofluids, polydisperse, aggregation, settling, alumina, microscopy, SAXS