Dispersing Alumina Nanoparticles Research Articles

Effect of Temperature and Nanoparticle Concentration on Free Convective Heat Transfer of Nanofluids

A theoretical analysis of the influence of temperature and nanoparticle concentration on free convection heat transfer from a horizontal tube immersed in an unbounded nanofluid was presented. The Nusselt (Nu) number and heat transfer coefficient were parameters of the intensity of the convective heat transfer. For free convection, the Nu number was a function of the Rayleigh (Ra) number and Prandtl (Pr) number. The Rayleigh (Ra) number and Prandtl (Pr) number were functions of the thermophysical properties of nanofluids. The thermophysical properties of nanofluids varied with temperature and nanoparticle concentration. Therefore, an analysis was conducted to evaluate the effects on the performance of nanofluids due to variations of thermal conductivity, viscosity, thermal expansion, density, and specific heat, which are functions of nanoparticle concentration and temperature. Water- and ethylene glycol (EG)-based nanofluids with dispersed alumina (Al2O3) nanoparticles at mass concentrations of 0.01%, 0.1%, and 1% were considered. Calculated Nu numbers and heat transfer coefficients were compared with experimental values taken from the published literature.

Efficacy of ultrasonic treatment for dispersing nanoparticles: A correlation with microstructure

In this study, an attempt was made to disperse 1 wt% of alumina nanoparticles (20–30 nm) in AZ91D matrix through two different methods (i) Mechanical Stirring (MS) and (ii) Mechanical stirring followed by Ultrasonic Treatment (MUST) at 1.75 kW/20 kHz. The density and porosity of both squeeze casted nanocomposites were determined. Further, the efficacy of UST for dispersing alumina nanoparticles was evaluated by examining the microstructure of nanocomposites through High Resolution Scanning Electron Microscopy (HR-SEM) and Optical Microscopy (OM). The HR-SEM images of MS revealed the formation of clusters of nanoparticles due to mechanical stirring. In the case of MUST, a prodigious improvement in the dispersion of nano particulates due to the application of UST was evident. This was confirmed by the instantaneous measurement of sizes of spots displayed in the HR-SEM images during the microstructure analysis. OM image showed significance in grain refinement for MUST composite as compared to MS. The average grain size was 310 µm and 175 µm for MS and MUST nanocomposites respectively.

Influence of Oxide Dispersoids on the Structure Development of Copper Nanocomposite Prepared by Spark Plasma Sintering Technology

Dispersion strengthened Cu composites are studied over recent years to find an optimum processing route to obtain a high strength, thermal-stable copper alloy designed for modern applications in electrical engineering. The experimental Cu–4Al2O3–1MgO material was prepared by in situ thermo-chemical technique and mechanical milling followed by spark plasma sintering (SPS). The study analyses the influence of the Al2O3 and MgO secondary phases on strengthening the copper matrix. Microstructure of the composite was studied by X-ray diffraction analysis, scanning and transmission electron microscopy. The sintered microstructure shows a grain size distribution characterized by ultrafine grains/twins embedded inside the matrix of nanocrystalline grains. The microstructure is thermal stable up to 900 °C due to the dispersed alumina nano-particles that effectively strengthen crystallite/grain boundaries during the SPS process and annealing of the sintered compact at elevated temperatures. On the other hand, the coarsened MgO particles are responsible for ultrafine grains/twins formation. The obtained microstructure is important for practical utilization of the material because this structure is characterized by a good combination of strength and ductility.

Formation Damage Induced by Water-Based Alumina Nanofluids during Enhanced Oil Recovery: Influence of Postflush Salinity.

Injecting nanofluids (NFs) has been proven to be a potential method to enhance oil recovery. Stranded oil is produced by wettability alteration where nanoparticles form a wedge film on pore wall surfaces, which is thought to shrink the pore space of the reservoir. Furthermore, ensuring the stability of the injected NF during the application is a major challenge. A low permeability reservoir and salinity of water make the response of NF injection to the formation damage more difficult. This article, therefore, studied the formation damage induced by the injection of alumina nanofluids (Al-NFs) in a relatively low permeability (7.1 mD) sandstone core. The salinity of the postflush water was also considered to mitigate the destructive impact. Al-NF was formulated by dispersing alumina nanoparticles (Al-NPs) in an aqueous solution of sodium dodecylbenzene sulfonate (SDBS) at its critical micelle concentration (CMC, 0.1 wt %). The formation damage, inherent to Al-NF injection, was evaluated by core-flooding tests. The assays consisted of the injection of 1 PV Al-NF (0.05 wt %) at the trail of which postflush at different salinities was flooded. The study found that the salinity of the postflush has an effect on the formation damage and oil recovery factor (RF). A chase water with a salinity concentration of 3 wt % sodium chloride (NaCl) produced an RF of 8.7% compared to a base case of water-flooding with a pressure drop of up to 13 MPa across the core (70 mm in length). These results pertained to the deposition of Al-NPs at the injection end. However, lowering the postflush salinity to 1 wt % NaCl mitigated the formation damage as evidenced by the decrease in pressure (35%) and an increase in RF to 17.2%.

Structural features of ultrafine-grained aluminum processed through accumulative roll bonding providing improved mechanical properties and thermal stability

Using transmission electron microscopy, tension and indentation tests we studied commercially pure aluminum processed by severe plastic deformation through accumulative roll bonding (ARB Al) and equal-channel angular pressing (ECAP Al) up to 8.0 von Mises equivalent strain to find the structural features providing improved mechanical properties and their enhanced thermal stability in the former case. It is revealed that the average size of the elements of the grain-subgrain structure is 23% lower and the strength properties are 19 – 27% higher in ARB Al with respect to ECAP Al. The physical reason for more refinement of the grain-subgrain structure and enhanced mechanical properties is the presence of dispersed alumina nanoparticles introduced into the bulk of ARB aluminum from the surface of the bonded stripes during ARB. The thermal stability of microhardness of ARB Al exceeds the respective value of ECAP Al in the temperature interval of 473 – 513 К, where the recrystallization starts to occur. The improved thermal stability of ARB Al is related to the higher resistance to recrystallization due to the presence of alumina nanoparticles on grain boundaries formed during ARB and precipitation of Si from the solid solution on these nanoparticles.

Effect of particle morphology on flexural properties of functionally graded epoxy-alumina polymer nanocomposite

Functionally graded polymer nanocomposites (FGPNC) were synthesized by dispersing alumina nanoparticles (spherical and rod shape) in epoxy by sonication technique. Gradation in the thickness direction was achieved by varying the wt% of nanoparticles. Samples of layered FGPNC were prepared by casting layers of neat epoxy and nanocomposites having 0.25, 0.5, 0.75 and 1 wt% of nanoparticles one by one in a vertical acrylic mould. Flexural properties of FGPNC samples were evaluated by three point bending method. FGPNC samples were loaded from neat epoxy side and nanocomposite side. Increments of 18% and 16% in flexural strength and 19% and 20% in flexural modulus were recorded for FGPNC with spherical and rod shape nanoparticles respectively compared to that of layered neat epoxy for loading from neat epoxy side. Whereas when load was applied from nanocomposite side, an improvement of 13% in flexural modulus of FGPNC was seen while flexural strength of FGPNC increased by 8%–9% over that of layered neat epoxy for both the types of nanoparticle.

Experimental investigation of the effect of dispersed silica and alumina nanoparticles on oil-aqueous phase interfacial tension

This work experimentally investigated silicon oxide and aluminum (III) oxide nanoparticles as enhanced oil recovery agents and their effects on wettability and interfacial tension of oil-wetted sandstone and carbonate rocks. The two nanoparticles were selected based on a screening of commercially available nanoparticles with considering the most important parameters. The required time and treatments for the rock samples to become oil-wet, and the required time for the nanofluid to treat each rock sample were also experimentally investigated. Results of this study show that the nanoparticles alter wettability of sandstone and carbonate rocks from oil-wet to water-wet state. It is also observed that sandstone samples are more effected than limestone ones and alumina nanoparticles have greater potential to alter the rock wettability.

The effects of alumina nanoparticles as fuel additives on the spray characteristics of gas-to-liquid jet fuels

The use of metal nanoparticles as fuel additives have gained interest due to its positive influence on liquid fuels’ combustion and emission performance. Nanoparticles dispersion affects the hydrodynamic and thermo-physical properties of the liquid fuel, and in turn, its atomization, mixing and evaporation characteristics. This work investigates the influence of nanoparticles dispersion on the spray performance of alternative gas-to-liquid (GTL) jet fuel under atmospheric ambient conditions. The spray characteristics of GTL fuel with dispersed alumina nanoparticles are compared with those of the pure GTL fuel. The spray characteristics at the macroscopic and microscopic levels are measured using the optical diagnostic techniques of shadowgraph and phase Doppler anemometry, respectively. The nanoparticles dispersed in liquid fuel tend to slightly alter the transient nature of the spray formation, enhance the liquid sheet instability and reduce the liquid sheet breakup length when compared to those of the pure GTL fuel. Furthermore, the mean droplet sizes of GTL fuel dispersed with nanoparticles are smaller than those of the pure GTL fuel.

Microstructure and Properties of Nanocrystalline Copper Strengthened by a Low Amount of Al2O3 Nanoparticles

Dispersion-strengthened Cu-Al2O3 materials have been studied over recent years to find an optimum processing route to obtain a high strength, thermal-stable copper alloy designed for modern applications in electrical engineering. The study analyses the influence of 1 vol.% of alumina content on strengthening the copper matrix. Microstructure of the Cu-Al2O3 composite was studied by x-ray diffraction as well as scanning and transmission electron microscopy. The composite shows a homogeneous, thermal-stable nanostructure up to 900 °C due to dispersed alumina nanoparticles. The particles effectively strengthen crystallite/grain boundaries in processes of powder consolidation and annealing of the compact. In contrast to monolithic Cu, the Cu-1 vol.% Al2O3 exhibits more than double strength and hardness. The nanocrystalline matrix and the low amount of alumina particles result in a yield strength of 288 MPa and a ductility of 15% which is a good combination for practical utilization of the material.

Solidification of a PCM with nanoparticles in triplex-tube thermal energy storage system

Effects of incorporating alumina nanoparticles on solidification of a phase-change material (PCM) in triplex-tube thermal energy storage (TES) system were numerically investigated in this study. A time-dependent, two-dimensional simulation of the entire solidification process was carried out for different nanoparticle loadings under constant charging temperatures of the heat transfer fluid (HTF). Results from this study were compared to previous related work and good agreement was obtained. Impacts of incorporating nanoparticles on flow structure and heat transfer characteristics over different stages of the PCM solidification process were also analyzed and discussed. Total solidification times were predicted for all nanoparticle volume fractions and inlet HTF temperatures considered. The results show that dispersing alumina nanoparticles of volumetric concentrations of 3–8% results in total time saving between 8% and 20%. The results also show that the presence of nanoparticles does not show much difference at the early stages of the solidification process, but as time elapses and/or volume fraction increases, the rate of solidification increases.

In Situ Preparation of Alumina Nanoparticles in Heavy Oil and Their Thermal Cracking Performance

This work details a technique for the in situ preparation of alumina nanoparticles in heavy oil and explores their activity with respect to mild thermal cracking. In principle, in situ-prepared nanoparticles display a high level of dispersion, which should improve their catalytic activity. Dispersed alumina nanoparticles 17 ± 5 nm in mean diameter were successfully prepared at 300 °C and characterized using X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The thermal cracking experiments were conducted in a batch reactor setup under two stages of heating at 300 and 350 °C. The pressure buildup in the reactor and the viscosity and °API gravity of the resultant oil were taken as measures of the extent of thermal cracking. Although there was a general shift toward higher °API gravity, it still fell within the level of uncertainty probably due to agglomeration at 350 °C that limited nanoparticle activity. A higher viscosity was obtained for the liquid fraction bec...

Development and characterization of high performance nano-hybrid GFRE composites for structural applications

The objective of this work is to enhance the mechanical properties of unidirectional [0]8 and quasi-isotropic [0/±45/90]s glass-fiber-reinforced composites by ultrasonically dispersing alumina-nanoparticles in epoxy matrix. The well dispersed alumina-nanoparticles in epoxy resin significantly improved the mechanical properties of alumina-nanocomposites. Results from fracture characterizations of the nano-hybridized unidirectional laminates with different off-axis angles showed high improvements in the interfacial bond strength between nanophased epoxy and glass fiber. Therefore, the flexural strength, modulus, and fracture toughness of quasi-isotropic laminate are significantly improved. Results from free vibration tests showed that the beam free length has high effects on the natural frequencies and the both have insignificant effect on the storage moduli of the composite laminates. For the investigated materials, the storage moduli correlated well (R2=0.99962) with the flexural moduli. The damping ratios of the nano-hybridized quasi-isotropic and unidirectional laminates are improved by 62% and 60%, respectively. These improvements, which were achieved through conventional processing, are essentially for developing the structural components of automotive and aerospace industry.

Specific heat of nanofluids synthesized by dispersing alumina nanoparticles in alkali salt eutectic

In this study, we report large enhancement in specific heat capacity of a eutectic salt mixture on dispersing alumina nanoparticles at 1% mass concentration. Eutectic of lithium carbonate and potassium carbonate (62:38 by molar ratio) was dissolved in distilled water with alumina nanoparticles at 1.0% mass concentration and with a nominal diameter of ∼10nm. The specific heat capacity measurement was performed using a differential scanning calorimeter (DSC). An alternate model involving in situ phase transformation was proposed which was found to be in good agreement with the variations observed in the experimental data for the different types of nanomaterial samples used in this study. These salt nanofluids can lead to the development of efficient thermal energy storage systems which in turn can enable significant reduction in the cost of solar power.

Wettability Alteration of Sandstone Cores by Alumina-Based Nanofluids

Wettability alteration can occur at different stages during the producing life of a reservoir. Oil recovery from oil-wet reservoirs can significantly be increased by altering its wettability from an oil-wet to a strongly water-wet condition. Chemical agents such as surfactants are known as wettability modifiers in oil-wet systems. More recently, nanofluids prepared by dispersing nanoparticles in several liquid agents have been considered as potential wettability modifiers. In this work, the effectiveness of alumina-based nanofluids in altering the wettability of sandstone cores with an induced oil-wet wettability was experimentally studied. Eight nanofluids with different nanoparticles concentration, ranging from 100 ppm to 10000 ppm, were prepared by dispersing alumina nanoparticles in an anionic commercial surfactant. The effect of nanofluids on wettability alteration was investigated by contact angle and imbibition tests, and it was shown that designed nanofluids could significantly change the wettabil...

EXPERIMENTAL STUDY OF CRITICAL HEAT FLUX WITH ALUMINA-WATER NANOFLUIDS IN DOWNWARD-FACING CHANNELS FOR IN-VESSEL RETENTION APPLICATIONS

The Critical Heat Flux (CHF) of water with dispersed alumina nanoparticles was measured for the geometry and flow conditions relevant to the In-Vessel Retention (IVR) situation which can occur during core melting sequences in certain advanced Light Water Reactors (LWRs). CHF measurements were conducted in a flow boiling loop featuring a test section designed to be thermal-hydraulically similar to the vessel/insulation gap in the Westinghouse AP1000 plant. The effects of orientation angle, pressure, mass flux, fluid type, boiling time, surface material, and surface state were investigated. Results for water-based nanofluids with alumina nanoparticles (0.001% by volume) on stainless steel surface indicate an average 70% CHF enhancement with a range of 17% to 108% depending on the specific flow conditions expected for IVR. Experiments also indicate that only about thirty minutes of boiling time (which drives nanoparticle deposition) are needed to obtain substantial CHF enhancement with nanofluids.

Investigation of Thermal Conductivity and Convective Heat Transfer of Alumina Nanofluids under Laminar Flow

In this research, dilute colloidal suspension alumina nanofluids were prepared by dispersing alumina nanoparticles in DI water and ethylene glycol as base fluids. Particle size analyzer and TEM test results revealed that the size of the alumina nanofluids(3wt% and 5wt%) with dispersion time 3hrs were 46nm and 60nm respectively. Thermal conductivity of these alumina nanofluids was measured by means of hot wire technique using a LAMBDA system. For water based alumina nanofluids, thermal conductivity enhancement was from 2.29% to 3.06% with 5wt% alumina at temperatures ranging from 15 to <TEX>$40^{\circ}C$</TEX>. Whereas in case of ethylene glycol based alumina nanofluids under the same temperature range, thermal conductivity enhancement was from 9.6% to 10% with 5wt% alumina. An enhancement of 37% average convective heat transfer was achieved with 5wt% alumina nanofluids at Re of 1,100.

Influence of Addition of Alumina Nanoparticles on Thermoelectric Properties of La-Filled Skutterudite CoSb&lt;sub&gt;3&lt;/sub&gt; Compounds

The CoSb3-based compound is a promising thermoelectric material useful in the temperature range of 600­900K. It, however, has a higher thermal conductivity. Thus, reducing the thermal conductivity causes improvement of the thermoelectric performance. In this work, we tried to reduce the thermal conductivity by both filling La and dispersing alumina nanoparticles (ANPs) into the compound. The raw powders of LaSb, Co, Ni, Sb and Te were prepared. The n-type La-filled compound was synthesized from the raw powders using a planetary ball mill. Then, ANPs were added to the combined powder and further mixed using the planetary ball milling. The mixture was sintered by a pulse-discharge sintering method. The combining phases of the samples were characterized by X-ray diffraction analysis. The thermoelectric properties were measured for the samples. Influence of addition of ANPs on the properties was studied. Adding 0.05mass% ANPs reduced the thermal conductivity. The sample added 0.5mass% or more ANPs increased both the electrical resistivity and the thermal conductivity. As a result, the sample added 0.05mass% ANPs had the maximum performance of ZT = 1.15 at 873K. [doi:10.2320/matertrans.E-M2012821]

Production of Highly Loaded Nanocomposites by Dispersing Nanoparticles in Epoxy Resin

AbstractThe objective of this study was the investigation of techniques for dispersing alumina nanoparticles with different surface modifications in epoxy resin. In order to prepare the matrix suspension, high contents of fillers (up to 50 wt %) were dispersed by conducting shear mixing techniques in a high performance laboratory kneader. The intention was to attain solutions that were stable against re‐agglomeration, while the mass fraction and the product fineness were maintained as high as possible. Therefore, both the formulations and the dispersion parameters were varied systematically. An epoxy resin was used as a carrier fluid and a corresponding amine hardener system was chosen. Tests were performed using alumina particles and surface modified alumina particles at different particle concentrations. Furthermore, the effect of diluting the colloidal suspensions and the resulting long term stability were also examined. The matrix suspension was examined with respect to viscosity, stability and particle size distribution.

Synthesis of copper alloys with extended solid solubility and nano Al2O3 dispersion by mechanical alloying and equal channel angular pressing

Cu–4.5 wt % Cr and Cu–4.5 wt % Cr–3 wt % Ag alloys, with and without nanocrystalline Al2O3 dispersions (particle size <10 nm), were synthesized by mechanical alloying/milling and consolidated by equal-channel angular pressing (ECAP) at ambient temperature. Microstructural characterization and phase analysis by X-ray diffraction, as well as scanning and transmission electron microscopy, provided evidence for the formation of a Cu-rich extended solid solution with nanometric (<30 nm) crystallite size after 25 h of milling, with uniformly dispersed alumina nanoparticles embedded in it. Consolidation of Cu–4.5 wt % Cr–3 wt % Ag alloy with 10 wt % nanocrystalline Al2O3 by eight ECAP passes was shown to result in a composite with an exceptionally large hardness of 390 VHN and enhanced wear resistance. The electrical conductivity of the pellets of the latter alloy without Al2O3 is about 30% IACS (international annealing copper standard), whereas pellets with 5 or 10 wt % Al2O3 dispersion exhibit a conductivity of about 20–25% IACS. Thus, the present room temperature synthesis and consolidation route appear to offer a promising avenue for developing high-strength, wear/erosion-resistant Cu-based electrical contacts with nano-ceramic dispersion.

Effect of nanoparticles and nanofibers on Mode I fracture toughness of fiber glass reinforced polymeric matrix composites

Abstract In the recent past, the research involving the fabrication and processing of reinforced polymer nanocomposites has increased significantly. These new materials are enabling in the discovery, development and incorporation of improved nanocomposite materials with effective manufacturing methodologies for several defense and industrial applications. These materials eventually will allow the full utilization of nanocomposites in not only reinforcing applications but also in multifunctional applications where sensing and the unique optical, thermal, electrical and magnetic properties of nanoparticles can be combined with mechanical reinforcement to offer the greatest opportunities for significant advances in material design and function. This paper presents two methods and material systems for processing and integration of the nanomaterial constituents, namely: (a) dispersing alumina nanoparticles using high energy mixing (using ultrasonication, high shear mixing and pulverization) and (b) electrospinning technique to manufacture nanofibers. These reinforced polymer nanocomposites and the processing methodologies are likely to provide effective means of improving the interlaminar properties of woven fiber glass composites compared to the traditional methods such as stitching and Z-pinning. The electrospinning technology relies on the creation of nanofibers with improved molecular orientation with reduced concentration of fiber imperfections and crystal defects. Electrospinning process utilizes surface tension effects created by electrostatic forces acting on liquid droplets, creating numerous nanofibers. These nanofibers thus have potential to serve as through-the-thickness reinforcing agents in woven composites. While the electrospun nanofibers provide bridging through-the-thickness reinforcement, the use of the nanoparticles influences the thermo-physical properties and provides an effective means from commercially available nanolevel material configurations to form reinforced polymer nanocomposites. Studies indicate that their mechanical behavior and performance however depends on incorporation, and functionalization of these alumina nanoparticles. Both these methods and material systems provide effective means for integrating the nanomaterial constituents into traditional fiber composite systems. In particular, this paper discusses the experimental study of the processing and delamination (interlaminar failure) characteristics (via Mode I fracture toughness assessment) of reinforced composite systems.