Al2O3 Suspensions Research Articles

Understanding the temperature dependence of thermo-physical properties of nanofluid suspensions using non-intrusive dynamic measurements

Thermal diffusivity dependence on temperature and concentration of aqueous colloidal suspensions of Al2O3 in deionized water has been investigated by conducting transient heat transfer experiments. The study has been performed in a purely non-intrusive manner using Mach Zehnder interferometry. Through the dependence of refractive index on temperature, the time sequence of recorded interferograms has been used to generate highly sensitive data of evolving temperature distribution in the thermal diffusion field. Determination of thermal diffusivity from temperature-position data has been carried out by the method of least square. In comparison with deionized water, substantial enhancement in thermal diffusivity with increasing temperature and concentration of nanofluid suspension of Al2O3 is observed through the time sequence of the recorded interferograms as well as through analytical measurements. Additionally, the measurement of ζ-potential, pH and effective viscosity of dilute Al2O3 suspension at various temperatures explains the possible mechanisms at micro-scale levels that are responsible for such an anomalous behaviour of thermal diffusivity. The competing interaction of these factors reveals dependence of thermal diffusivity on particle cluster formation and thereby in the resultant stability of the suspension. The experimental findings indicate that, at specific size and shape, the higher conductivity of solid alumina particles and their cluster formation plays a major role in enhancing the thermophysical properties of the nanofluid Al2O3 suspension over the considered range of temperature and concentration. Also, a reasonably close agreement of the obtained trends of thermal diffusivity values with those reported in the literature and clear visualization of enhancement in thermal transport through interferograms signifies the importance of the proposed non-intrusive measurement technique for reliable measurement of thermal properties of nanofluids.

Effect of aluminum oxide and reduced graphene oxide mixtures on critical heat flux enhancement

Pool boiling experiments were carried out to investigate critical heat flux (CHF) characteristics in mixtures of aluminum oxide (Al2O3) nanoparticles and reduced graphene oxide (RGO) colloids under saturated temperature and atmospheric pressure conditions. Nichrome (Ni-Cr) wire (diameter: 0.2mm; length: 85mm) was fixed between electrodes horizontally and heated using Joule heating. The working fluids were prepared using different concentrations of Al2O3 suspension (0.0001–0.01vol%) and RGO colloids (0.00005–0.005vol%), in concentration ratios varying from 0.25 to 10. Deionized water was used as a control. In the Al2O3 suspensions, the CHF increased with concentration, showing a saturated enhancement of 54% above 0.001vol% concentration. In the RGO colloids, CHF enhancement varied between 10 and 37% as the concentration increased. A dramatic CHF enhancement of 473% was observed when the Al2O3/RGO mixture was equally mixed at 0.0005vol% of each (sample: A0005R0005). Upon completion of the pool boiling experiments, a coating layer was observed on each specimen; the coating layer and specimen surface were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. When Al2O3 and RGO were used as individual working fluids, the morphologic characteristics of the coating layer were similar to typical shapes seen in previous reports. Upon altering the concentration ratio, different clusters of Al2O3 and RGO flakes appeared in the coating layer, providing coating layers of different appearances. A porous superstructure formed in A0005R0005 and the macrostructure consisted of Al2O3 and RGO agglomerations. The enhancement mechanisms could not be explained based solely on the hydrophilic contact angle. Therefore, an additional experiment to quantify capillary flow rate through the porous media was performed with consideration of the marginal heat flux gain.

Rheological behavior of Al2O3 suspensions containing polyelectrolyte complexes for direct ink writing

Al2O3 polyelectrolyte suspensions containing PAA-PEI complexes have been used for direct ink writing to fabricate complex 3D structures with micro-sized feature. Zeta potential and rheological behavior of the Al2O3 polyelectrolyte suspensions were investigated. The isoelectric point of Al2O3 particles shifts from alkaline region to acidic region as the [COOH]:[NHx] ratio increases from 0.12 to 3. The rheological results reveal that the 40vol% Al2O3 suspension with [COOH]:[NHx] ratio of 0.3 and 15mg/mL methylcellulose at pH10 is the optimal suspension for direct ink writing, due to its good shear thinning and viscoelastic behavior. The filament in lattice structure prepared using this polyelectrolyte suspension can maintain its original shape with little spreading. In the micrograph of sample sintered at 1600°C for 2h, the uniform size of grains indicates that the structure is fully sintered under this sintering condition.

Size distribution of nanoparticles in the droplets ultrasonically atomized from Al2O3 suspension

In this study, a recollection method only for particles below a certain size involving ultrasonic atomization was suggested. Nanoparticles were separately recollected by using the suggested method with the suspension made of alumina powder of 300 nm center diameter and the particle distributions in the recollected suspension were observed using an optical microscope. Furthermore, the size distribution of the recollected particles depending on the surface tension of the suspension was investigated. Results indicate that the sizes of the particles in the recollected suspension were reduced by decreasing the surface tension of the suspension. In the suggested method, the maximum diameter of the recollected nanoparticles could be controlled by changing the surface tension of the suspension.

Al2O3\u2013TiO2/ZrO2\u2013SiO2 based porous ceramics from particle-stabilized wet foam

The porous ceramics based on Al2O3–TiO2/ZrO2–SiO2 from particle-stabilized wet foam by direct foaming were discussed. The initial Al2O3–TiO2 suspension was prepared by adding TiO2 suspension to partially hydrophobized colloidal Al2O3 suspension with equimolar amount, to form Al2TiO5 on sintering. The secondary ZrO2–SiO2 suspension was prepared using the equimolar composition, and to obtain ZrSiO4, ZrTiO4, and mullite phases in the sintered samples, the secondary suspension was blended into the initial suspension at 0, 10, 20, 30, and 50 vol%. The wet foam exhibited an air content up to 87%, Laplace pressure from 1.38 to 2.23 mPa, and higher adsorption free energy at the interface of approximately 5.8×108 to 7.5×108 J resulting an outstanding foam stability of 87%. The final suspension was foamed, and the wet foam was sintered from 1400 to 1600 °C for 1 h. The porous ceramics with pore size from 150 to 400 μm on average were obtained. The phase identification was accomplished using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermogravimetric analysis (TGA), and microstructural analysis was performed using field emission scanning electron microscopy (FESEM).

Numerical Analysis of Unsteady Conjugate Natural Convection of Hybrid Water-Based Nanofluid in a Semicircular Cavity

Unsteady conjugate natural convection in a semicircular cavity with a solid shell of finite thickness filled with a hybrid water-based suspension of Al2O3 and Cu nanoparticles (hybrid nanofluid) has been analyzed numerically. The governing equations for this investigation are formulated in terms of the dimensionless stream function, vorticity, and temperature and have been solved by the finite difference method of the second-order accuracy. The effects of the dimensionless time, Rayleigh number, thermal conductivity ratio, and the nanoparticles volume fraction on the flow patterns and heat transfer have been studied. The obtained results have revealed essential heat transfer enhancement at solid–fluid interface with addition of nanoparticles. In addition, a comparison of the heat transfer enhancement level due to the suspension of various nanoparticles materials (Al2O3 and Cu) in water as regular nanofluids (Al2O3/water and Cu/water) and as a hybrid Al2O3–Cu/water nanofluid is reported.

Tribological Performance and Lubrication Mechanism of Alumina Nanoparticle Water-Based Suspensions in Ball-on-Three-Plate Testing

The lubrication performance of alumina (Al2O3) nanoparticle water-based suspensions was systematically investigated using a ball-on-three-plate testing configuration with alloy steel on stainless steel contact. The size and concentration of Al2O3 nanoparticle were varied to obtain optimal performance. The effects of testing load, sliding speed and contact surface roughness on the lubrication performance of the Al2O3 suspensions were investigated. It was found that 1 to 2 wt.% 30 nm Al2O3 nanoparticle suspensions showed up to 27% friction and 22% wear reduction, in comparison with water glycerol solution. Under different testing conditions, the suspensions also showed noticeably more stable and improved tribological performance. Wear mark analysis revealed that during tribological testing the nanoparticles formed a layer of dynamically balanced tribo-thin film, preventing the direct contact between asperities of alloy steel ball and stainless steel plate. The nanoparticles were also believed to fill up the trenches of the plate surface through mending effect and carry the wear debris induced in running-in period to avoid abrasive wear.

Highly-closed/-Open Porous Ceramics with Micro-Beads by Direct Foaming

This study reports on wet-foam stability with respect to porous ceramics from a particle-stabilized colloidal suspension that is achieved through the addition of polymethyl methacrylate (PMMA) using a wet process. To stabilize the wet foam, an initial colloidal suspension of Al₂O₃ was partially hydrophobized by the surfactant propyl gallate (2 wt.%) and SiO₂ was added as a stabilizer. The influence of the PMMA content on the bubble size, pore size, and pore distribution in terms of the contact angle, surface tension, adsorption free energy, and Laplace pressure are described in this paper. The results show a wet-foam stability of more than 83%, which corresponds to a particle free energy of 2.7 × 10 −12 J and a pressure difference of 61.1 mPa for colloidal particles with 20 wt.% of PMMA beads. It was possible to control the uniform distribution of the open/closed pores by increasing the PMMA content and by adding thick struts, leading to the achievement of a higher-stability wet foam for use in porous ceramics.

Alumina/copper foams produced by replica using a double impregnation process

ABSTRACTRheological behaviour of Al2O3 and CuO suspensions was characterised in order to fabricate Al2O3/Cu foams as an alternative way to produce foams with better mechanical properties than common Al2O3 foams. Different quantities of raw materials were combined to select the formulations for the ceramic-metal foams. Foams were produced by a double impregnation process, followed by a thermal cycle and a reduction cycle. In this work, materials were characterised trough zeta potential, SEM and optical dilatometry. Foams microstructure and compressive strength were evaluated. Final structures had a compressive resistance of 0.44 ± 0.14 MPa.

Parabolic Trough System Operating with Nanofluids: Comparison with the Conventional Working Fluids and Influence on the System Performance

To analyse the behaviour of a parabolic trough operating with nanofluids, and compare its performance to the more traditional ones using oil, a model for the thermal analysis of the system has been developed and implemented in Matlab. The simulations have been performed for a suspension of Al2O3 in synthetic oil and its characteristics compared to the corresponding basic liquid used by itself. The string has been assumed to have a length of 100 m and a concentrating surface area of 550 m2. The simulations have been carried out for different DNI (Direct normal irradiance) and variable mass flow, ensuring a temperature at the collector outlet below 400̊C. For a proper comparison, the following variables and efficiency indicators have been checked: power output, pumping power, thermal efficiency and overall efficiency of the parabolic trough system.

Preparation of Capped Octahedral OsHC6 Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC6 complexes. Reactions of the dimer [OsCl2(η6-p-cymene)]2 (1) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1H-benzimidazolylidene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1H-benzimidazolylidene (PhMeBIm*)) afford OsCl2(η6-p-cymene)(PhMeL) (L = BIm (2), BIm* (3)), which undergo cyclization to give OsCl{κ2-C,C-(MeL-C6H4)}(η6-p-cymene) (L = BIm (4), BIm* (5)) by stirring in dichloromethane suspensions of Al2O3. Complexes 4 and 5 exchange the anion with AgOTf (OTf = CF3SO3). In acetonitrile, at 75 °C, the resulting OTf derivatives Os(OTf){κ2-C,C-(MeL-C6H4)}(η6-p-cymene) (L = BIm (6), BIm* (7)) release the arene to yield the tetra(solvento) compounds [Os{κ2-C,C-(MeL-C6H4)(CH3CN)4]OTf (L = BIm (8), BIm* (9)). Complexes 8 and 9 react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os{κ2-C,C-(MeL-C6H4)(PhMeL)(CH3CN)3]OTf (L = BIm (10), BIm* (11)), containing a C...

Impact of anionic polyacrylamide on stability and surface properties of the Al2O3-polymer solution system at different temperatures.

The stability mechanism and thermal properties of the system alumina–anionic polyacrylamide (PAM) was studied. The polymer’s adsorption properties in dependence on the following parameters solution pH (in the range 3–9), temperature (in the range 15–35 °C), and carboxyl groups’ content in the PAM chains (in the range 5–30 %) were examined. The turbidimetry method was applied for determination of the suspension stability of alumina in the presence of PAM. The obtained results indicate that the polymer addition improves significantly Al2O3 suspension stability at pH 6 and 9 (in the whole examined temperature range). PAM containing a larger number of carboxyl groups stabilizes solid particles more effectively (due to greater contribution of electrosteric interactions). Moreover, the polymer adsorption on the alumina surface causes changes in the thermal stability of the examined systems. In dependence on temperature, the higher the content of carboxyl groups in the PAM molecules, the greater the total mass loss. This is due to increased adsorption of polyacrylamide whose chains contain numerous –COOH groups.Electronic supplementary materialThe online version of this article (doi:10.1007/s00396-016-3906-7) contains supplementary material, which is available to authorized users.

Enhancement of laminar convective heat transfer using microparticle suspensions

This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al2O3, Co3O4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al2O3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al2O3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.

Erratum: POEGMA‐b‐PAA comb‐like polymer dispersant for Al2 suspensions

Article First Published online: 9 March 2016 DOI: 10.1002/app.43577 [Article in J. Appl. Polym. Sci. 2016, 133, DOI: 10.1002/app.43352] In the published article cited above, the title was incorrectly given as “POEGMA-b-PAA comb-like polymer dispersant for Al2 suspensions”. The correct title is “POEGMA-b-PAA comb-like polymer dispersant for Al2O3 suspensions”. The publisher regrets any inconvenience this may have caused.

Ultrasonic wave velocity in the restructuring of disperse media

The ultrasonic wave velocities in the restructuring of disperse media were measured using interference and pulsed techniques and the coefficient of reflection in suspensions of starch, Al2O3, and SiO2 particles, glass bulbs, their porous sediments, and composites of Fe3O4 particles in 10% gelatin aqueous solution at a frequency of 3 MHz. The experiments showed alternating variation in the concentration velocity coefficient during the transition of the dispersed phase concentration from the subpercolation to percolation region. The minimum ultrasonic wave velocity in the region of discrete clusters correlates with the ratio between the particle and matrix densities. The results obtained are explained using the Isakovich, Chaban, Rytov, Biot, Hausdorff, and other theories.

POEGMA‐b‐PAA comb‐like polymer dispersant for Al2 suspensions

ABSTRACTPOEGMA‐b‐PAA comb‐like polymer is synthesized through RAFT polymerization, and it is employed as an efficient dispersant for Al2O3 suspensions. The POEGMA‐b‐PAA polymer consists of PAA chains and POEGMA comb‐like chains. The former provide electrostatic attraction between Al2O3 particles and polymer, while the latter extend to solution and maintain the stability of suspension due to strong steric hindrance. The adsorption is proven and the rheology behaviors of Al2O3 suspensions are strongly improved. Different POEGMA‐b‐PAA polymers with different length of side chains have similar but not identical rheological properties. The polymer with the appropriate length of side chain provides the biggest improvement to rheological properties of Al2O3 suspensions, such as apparent viscosity and granularity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43352.

Hybrid Water-Based Suspension of Al2O3 and Cu Nanoparticles on Laminar Convection Effectiveness

A numerical investigation of a laminar forced convection of different working fluids including pure water, various volume concentrations of a nanofluid ( nanoparticles dispersed in water), and a hybrid water-based suspension of and Cu nanoparticles (which is a new advanced nanofluid with two kinds of nanoparticle materials) in a uniformly heated circular tube is accomplished. In this paper, the effect of using hybrid water-based suspension on thermal behavior and hydrodynamic performance in a range of Reynolds number in the laminar regime is investigated. Then, a comparison is made between the thermal and hydrodynamics behavior of the hybrid suspension with those of the nanofluid (with the same concentration) and the conventional one. It is observed that, for all Reynolds numbers studied, employing the hybrid suspension improves the heat transfer rate compared to pure water and the nanofluid. Nevertheless, it reveals an adverse effect on the wall shear stress and friction factor due to the presence of nanoparticles. However, the average increase of overall Nusselt number (rather to pure water) in hybrid suspension is 7.20%, whereas is is 10.94% for the average increase of the friction factor.

Mechanical and thermal properties of highly porous Al2TiO5–Mullite ceramics

Al2TiO5–mullite porous ceramics were synthesized by direct foaming method using α-Al2O3, TiO2 and SiO2 as starting materials. The initial suspension for Al2TiO5 was prepared by adding TiO2 suspension to the equimolar amount of partially hydrophobized colloidal Al2O3 suspension. A secondary suspension was prepared using following molar composition 3:2 Al2O3/SiO2 and it was blended to the initial suspension in (0, 10, 20, 30 and 50)vol% to obtain the mullite phase in the sintered sample. Thermal expansion coefficient and thermal hysteresis curves of the porous ceramic samples with pure Al2TiO5 and of the Al2TiO5 ceramic with mullite addition were measured. Hertzian indentations are used to evaluate the damage behavior under constrained loading conditions. Mechanical behavior from indentation load–displacement curves is investigated.

Synthesis of the RGO/Al2O3 core–shell nanocomposite flakes and characterization of their unique electrostatic properties using zeta potential measurements

The aim of this study was to describe the influence of the modification of electrostatic properties of RGO/Al2O3 core–shell nanocomposite flakes. The amount of crystalline form of aluminum oxide was very small. It existed mostly in amorphous phase in the form of covalently bonded to GO surface. The morphological, structural and physicochemical investigations results showed that spherical Al2O3 nanoparticles (ca. 41nm) in gamma phase completely covered the surface of curly-shaped RGO flakes and acted as a spreader between individual flakes. The high BET specific surface area of the analyzed composite (119.71m2/g) together with very low open porosity (0.479cm3/g) indicated that RGO/Al2O3 nanocomposite flakes showed low tendency to agglomeration. The zeta potential curves obtained for RGO/Al2O3 core–shell nanocomposite flakes were differing from curves obtained for GO and Al2O3 suspensions in distilled water and neutral environment. The specific electrostatic properties of the core–shell system of RGO/Al2O3 flakes had an influence on its surface charge (zeta potential) which was measured by applying an external electric field. The FTIR and Raman investigations results also confirmed that the CO species were not taking part in the surface amphoteric reactions resulting in the formation of electrostatic surface charge.

Improvement of CO2 absorption using AL2O3 nanofluids in a stirred thermostatic reactor

The improvement of CO2 absorption by Al2O3 nanofluids with deionized water as the base fluid was studied experimentally. The reactor used was a stirred thermostatic reactor, operated batchwise. Pure CO2 was employed in all the experiments. The content of Al2O3 in nanofluids ranged from 0 to 0.2 % (wt). Sodium dodecyl benzene sulfonate (SDBS) was employed to improve the stability of the nanofluids, and the combined effect of nanoparticles and surfactants on the absorption enhancement was studied. The parameters such as the concentration of Al2O3 nanoparticles and surfactants, the stirring speed, and the ultrasonic time were varied. The results show that the nanoparticle mass fraction and the ultrasonic time have an optimum value for the CO2 absorption enhancement. The combination of surfactants and nanoparticles improves the enhancement performance of Al2O3 nanofluids more effectively than that without surfactants. With the increase of the stirring speed, the effective absorption ratio in stable nanofluids declines, while in poorly dispersed Al2O3 suspensions, it is increased first and then reduced. The mechanism of the Al2O3 nanofluid enhancing CO2 absorption is discussed accordingly. The absorption enhancement by the Al2O3 nanofluid is mainly attributable to convective motion induced by the Brownian motion.