Water-based Alumina Research Articles

Experimental evaluation of the effect in the stability and thermophysical properties of water-Al2O3 based nanofluids using SDBS as dispersant agent

Nanofluids are thermo-fluids engineered by dispersing nanosized particles in conventional base fluids used in heat transfer applications. In this experimental study, the temporal stability and thermophysical properties of water-based alumina nanofluids, such as thermal conductivity, surface tension and viscosity, were evaluated at three different concentrations (0.1 wt%, 0.5 wt%, and 1.0 wt%) using sodium dodecyl benzene sulfonate (SDBS) as dispersant agent. The results showed that the nanofluid prepared with 1.0 wt% exhibits thermal conductivity enhancements between 11% and 15% compared to deionized water. Additionally, a pseudoplastic behaviour was identified by means of a rheological study, which increased as the nanoparticle concentration increased. Nevertheless, the nanofluids with SDBS showed a Newtonian behaviour and viscosity values close to those of water, which is suitable to avoid frictional losses in pump processes. In turn, surface tension increases with the amount of DI-water in Al2O3 concentrations, but it decreases with the addition of SDBS, which has an important effect on the boiling applications of nanofluids. This work was carried out to highlight the importance of nanofluids stability in function of the surfactant added and the nanoparticle concentration, in the measurement of significant thermophysical properties such as surface tension, viscosity and thermal conductivity, which could be used to explain the nanofluids behaviour in different thermal devices.

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.

Experimental study of cooling performance of water-based alumina nanofluid in a minichannel heat sink with MEPCM layer embedded in its ceiling

This work investigates experimentally the cooling performance of Al2O3/water nanofluid with 8 wt% concentration flowing through a minichannel heat sink with a MEPCM layer in its ceiling. The hydrothermal characteristics of the nanofluid-cooled minichannel heat sink are analyzed and the dimensionless wall temperature distribution, Nusselt number, heat transfer effectiveness, coefficient of performance, figure of merit, and wall temperature thermal resistance are assessed. The measured results show that the dispersion of alumina nanoparticles inside pure water declines the wall temperature and consequently enhances the heat transfer effect and Nusselt number augments. The maximum values of average heat transfer effectiveness and FOM at the inlet of the MCHS are achieved 1.4 and 1.27 by flowing nanofluid with 8 wt% nanoparticle concentration and Re = 1549, respectively. The results revealed that embedding MEPCM layer in the ceiling of the MCHS has little influence on the cooling performance of Al2O3/water nanofluid in the minichannel heat sink.

Experimental study of cooling characteristics of water-based alumina nanofluid in a minichannel heat sink

This paper investigates experimentally the convection heat transfer of Al2O3/water nanofluid with 0–8 wt% concentrations flowing through a parallel minichannel heat sink. A uniform heat flux in the range of 1.2–6.8 W/cm2 is applied for heating the heat sink and the Reynolds number is considered in the range of 238–1549. The measured results reveal that the increment of concentration and decrement of flowrate lead to the increase of friction factor. The maximum nanofluid to pure water pressure drop ratio of 1.41 is observed by flowing nanofluid with 8% nanoparticle concentration for Reynolds number of 258. Moreover, it is found that the values of heat transfer effectiveness and figure of merit are more than unity, indicating the beneficial application of Al2O3/water nanofluid as the coolant in the heat sink. The maximum values of heat transfer effectiveness and figure of merit are achieved 1.4 and 1.27 by flowing 8 wt% nanofluid for Reynolds number of 1549. Furthermore, the addition of nanoparticle content decreased the coefficient of performance and the highest value belongs to the pure water. The increment of Reynolds number and nanoparticle content significantly decrease the thermal resistance.

Effects of Viscosity Variations on Buoyancy-Driven Flow from a Horizontal Circular Cylinder Immersed in Al2O3-Water Nanofluid

The buoyancy-driven boundary-layer flow from a heated horizontal circular cylinder immersed in a water-based alumina (Al2O3) nanofluid is investigated using variable properties for nanofluid viscosity. Two different viscosity models are utilized to evaluate heat transfer enhancement from a cylinder. Exact analytic solutions of the problem are attained employing a novel powerful technique is known as the Optimal Homotopy Analysis Method (OHAM). The accuracy and reliability of the results are verified by comparing them with experimental results in the literature. It is found that the characteristics of flow and temperature distributions are significantly influenced by the volume fraction of alumina nanoparticles, as well as nanofluid viscosity models. Enhancing the volume fraction of nanoparticles, the surface shear stress and the local Nusselt number both increase in the middle regions of the cylinder. The results also indicated that with increasing the nanoparticles volume fraction, isotherms become less dense and the absolute values of the stream-function decrease within the domain. Based on the results of the parametric study, two correlations (based on two different effective viscosity models) are proposed for the average Nusselt number of the alumina-water nanofluid in terms of volume fraction of the nanoparticles and the Rayleigh number which can be used as benchmarks for future investigations. However, uncertainties of viscosity models showed different manners on heat transfer coefficient versus nanoparticles volume fraction.

Laminar Mixed Convection of Water-Based Alumina Nanofluid in a Cylindrical Enclosure with a Rotating End Wall: A Numerical Investigation

Steady-state laminar mixed convection of water-based alumina nanofluids in cylindrical enclosures with a rotating top cover has been numerically analyzed for different Reynolds numbers (500–3000), Richardson numbers (0–1) and nanoparticle volume fractions (1–5%) for an aspect ratio of unity. Two different configurations have been considered for this analysis in order to obtain physical insights into the fluid flow and heat transfer in cylindrical enclosures with a rotating end cover. In one configuration (i.e. C1 configuration), the rotating top wall is kept at a higher temperature than the bottom wall, whereas the bottom wall is heated in the second configuration (i.e. C2 configuration). The mean Nusselt number in the case of mixed convection has been found to assume higher values in the C2 configuration than in the C1 configuration for a given set of values of Reynolds number, Richardson number and nanoparticle volume fraction. It has also been found that mean Nusselt number monotonically decreases with increasing nanoparticle volume fraction regardless of Richardson number values in the C2 configuration, whereas the mean Nusselt number decreases (increases) with increasing nanoparticle volume fraction for fully forced convection (mixed convection) in the C1 configuration. The simulation data has been used to propose a correlation for the mean Nusselt number for both C1 and C2 configurations.

Comparative study of heat transfer and friction characteristics of water-based Alumina–copper and Alumina–CNT hybrid nanofluids in laminar flow through pipes

In this experimental work, a comparative study of convective heat transfer and drop in pressure characteristics of Alumina–Cu/water and Alumina–CNT/water hybrid nanofluids in fully developed laminar flow in a uniformly heated tube with circular cross section is presented. For this, Alumina–Cu hybrid nanoparticles (90:10 proportion was taken. Below this proportion for, e.g., 80:20, the nanofluid was not stable. Coagulation was happening) were prepared by using a hydrogen reduction technique. Characterization was done for the prepared powder through XRD and scanning electron microscope (SEM) to validate the chemical constitution, to establish the size of the particle and to investigate the morphology of surface. The synthesized Alumina–Cu hybrid nanopowder is dispersed in deionized water in an ultrasonic bath to form a well-dispersed 0.1% volume concentration of hybrid nanofluid. Carbon nanotube (CNT) functionalization was done by acid treatment method to convert the CNT surface from hydrophobic to hydrophilic. Scanning electron microscope was used for characterization of the aluminum oxide particles and functionalized multi-walled carbon nanotubes. To prepare 0.1% volume fraction of Alumina–CNT/water nanofluid, required quantities of Alumina powder and functionalized CNT were dispersed in deionized water in 90:10 proportion. Experiments were conducted in the laminar flow range with water, Alumina/water and hybrid nanofluids, and the results obtained have been compared. The convective heat transfer experimental results showed greater enhancement with Alumina–CNT/water hybrid fluid compared to Alumina–Cu/water hybrid fluid. The maximum enhancements of 30.65% and 20.48% in Nusselt number have been obtained for 0.3% volume fraction of Alumina–CNT/water hybrid nanofluid and Alumina–Cu/water hybrid nanofluid, respectively, at Reynolds number of 1350 as compared to the Nusselt number of water.

Heat and mass transfer characteristics of MHD three-dimensional flow over a stretching sheet filled with water-based alumina nanofluid

PurposeThis paper aims to understand the influence of velocity slip, nanoparticle volume fraction, chemical reaction and non-linear thermal radiation on MHD three-dimensional heat and mass transfer boundary layer flow over a stretching sheet filled with water-based alumina nanofluid. To get more meaningful results, the authors have taken nonlinear thermal radiation in the heat transfer process.Design/methodology/approachSuitable similarity variables are introduced to convert governing partial differential equations into the set of ordinary differential equations, and are solved numerically using a versatile, extensively validated finite element method with Galerkin’s weighted residual simulation. The velocity, temperature and concentration profiles of nanoparticles as well as skin friction coefficient, Nusselt number and Sherwood number for different non-dimensional parameters such as volume fraction, magnetic, radiation and velocity slip parameters as well as the Prandtl number are examined in detail, and are presented through plots and tables.FindingsIt is noticed that the rate of heat transfer enhances with higher values of nanoparticle volume fraction parameter. It is worth mentioning that the heat transfer rates improve as the values of increase. Increasing values of M, R, θw and β decelerates the thickness of the thermal boundary layer in the fluid regime. The heat transfer rates decelerate as the values of suction parameter increase.Originality/valueThe authors have written this paper based on the best of their knowledge on heat and mass transfer analysis of nanofluids. The information in this paper is new and not copied from any other sources.

Heat transfer and pressure drop performance of alumina–water nanofluid in a flat vertical tube of a radiator

ABSTRACT This work presents experimental investigation on the effects of nanofluid inlet temperature (40–90°C), Reynolds number (12,000–30,000), particle concentration (0–1 vol.%), and air velocity (0.25–0.55 m/s) on thermal and flow characteristics of water-based alumina nanofluids in a flat vertical tube of a radiator. The specific heat capacity, viscosity, density, and thermal conductivity were measured experimentally. The heat transfer coefficient enhanced (up to 31%) with an increase in fluid inlet temperature, particle volume concentration, Reynolds number as well as air inlet velocity. The pressure drop increased with an increase in the particle volume concentration and Reynolds number, while it decreased slightly with an increase in the fluid inlet temperature. The friction factor and pumping power increased with particle concentration. The friction factor decreased, while the pumping power increased with sn increase in fluid flow rate.

Finite element computation of magnetohydrodynamic nanofluid convection from an oscillating inclined plate with radiative flux, heat source and variable temperature effects

This work describes finite element computations for radiative magnetohydrodynamic convective Newtonian nanofluid flow from an oscillating inclined porous plate with variable temperature. Heat source/sink and buoyancy effects are included in the mathematical model. The problem is formulated by employing Tiwari–Das nanofluid model, and two water-based nanofluids, copper and alumina, with spherical shaped metal nanoparticles are considered. The Brinkman and Maxwell–Garnetts models are used for the dynamic viscosity and effective thermal conductivity of the nanofluids, respectively. An algebraic flux model, the Rosseland diffusion approximation, is adopted to simulate thermal radiative flux effects. The dimensionless, coupled governing partial differential equations are numerically solved via the finite element method with weak variational formulation by imposing initial and boundary conditions with a weighted residual scheme. A grid independence study is also conducted. The finite element solutions are reduced to known previous solutions in some limiting cases of this investigation and are found to be in good agreement with published work. This investigation is relevant to electromagnetic nano-material manufacturing processes operating at high temperatures where radiation heat transfer is significant.

Rayleigh–Benard convection in water-based alumina nanofluid: A numerical study

ABSTRACTRayleigh–Benard (R-B) convection in water-based alumina (Al2O3) nanofluid is analyzed based on a single-component non-homogeneous volume fraction model (SCNHM) using the lattice Boltzmann method (LBM). The present model accounts for the slip mechanisms such as Brownian and thermophoresis between the nanoparticle and the base fluid. The average Nusselt number at the bottom wall for pure water is compared to the previous numerical data for natural convection in a cavity and a good agreement is obtained. The parameters considered in this study include the Rayleigh number of the nanofluid, the volume fraction of alumina nanoparticle and the aspect ratio of the cavity. For the Al2O3/water nanofluid, it is found that heat transfer rate decreases with an increase of the volume fraction of the nanoparticle. The results are demonstrated and explained with average Nusselt number, isotherms, streamlines, heat lines, and nanoparticle distribution. The effect of nanoparticles on the onset of instability in R-B convection is also analyzed.

Thermal evaluation of water-based alumina nanofluid in an electronic heat sink application

An experimental study was conducted to investigate the thermal performance of a water-based Al2O3 nanofluid in an electronic heat sink application. Heat transfer tests were carried out using 20 nm alumina particles at a concentration of 5% by mass, and a coolant temperature ranging from 47 to 57 oC. The results were compared to a baseline case using deionized water as a coolant. Thermal conductivity and viscosity tests conducted on alumina nanofluids show both parameters increase with nanoparticles mass concentration. Alumina nanofluid with 5% nanoparticles mass concentration behaves as a shear thinning fluid. Tests conducted on an electronic heat sink show heat flux and coolant heat transfer coefficient increase with bulk mass flow rate. Compared to cooling by deionized water, the average increase in the heat transfer coefficient using water-based alumina nanofluid as a coolant was about 20%, while the average increase in heat flux was about 24%. An additional decrease in the heated wall cross-section temperature between 4.1 and 4.9 oC is also seen. For the same pumping power, the presence of nanoparticles in the base fluid is shown to have a significant effect on the increase in heat transfer coefficient.

Thermal performance evaluation of a helically-micro-grooved heat pipe working with water and aqueous Al2O3 nanofluid at different inclination angle and filling ratio

The present work reports the thermal performance of a helically-micro-grooved heat pipe working with water-based alumina nanofluid. The effects of the inclination angle (0°, 30°, 60° and 90°), filling ratio (20, 40, 60 and 80%) and heat input (45:65W) on heat transfer characteristics of the heat pipe using either distilled water or water-based alumina nanofluid with the volume concentration of Al2O3 nanoparticles of 3.0% are experimentally investigated. Results revealed that the thermal performance of the heat pipe enhances with nanofluid compared to DW and both inclination angle and filling ratio significantly affect the thermal performance of the heat pipe. The evaporation and condensation heat transfer coefficients increase as filling ratio increases, but thermal resistance decreases when filling ratio increases. Moreover, the inclination angle of 60° achieves the best thermal performance of the heat pipe using water or nanofluid. The evaporation and condensation heat transfer coefficients of nanofluid are higher than those of water by 30.4% and 11.1%, respectively, while the thermal resistance of nanofluid is lower than that of water by about 18.2%.

Forced convection of nanofluid flow across horizontal circular cylinder with convective boundary condition

A numerical investigation has been conducted to investigate the steady forced convection boundary layer nanofluid flow past a horizontal circular cylinder placed in water-based copper (Cu) and alumina (Al2O3) nanofluids. Using appropriate transformations, the system of partial differential equations is converted into an ordinary differential system of three equations, which is solved numerically using Keller box and Newton-Raphson methods. The effects of thermal and solutal convective boundary conditions are taken into account which makes the present analysis practically applicable. Numerical results are obtained for the dimensionless velocity, temperature and concentration as well as the skin-friction, Nusselt and Sherwood numbers for specific values of the governing parameters with fixed Prandtl number (Pr=6.2) and Schmidt number (Sc=0.68) for water. It is shown that, for a regular fluid (ϕ=0), a very good agreement exists between the present numerical results and those reported in open literature.

The study of electrical conductivity and diffusion behavior of water-based and ferro/ferricyanide-electrolyte-based alumina nanofluids

Nanofluids are liquids containing suspensions of solid nanoparticles and have attracted considerable attention because they undergo substantial mass transfer and have many potential applications in energy technologies. Most studies on nanofluids have used low-ionic-strength solutions, such as water and ethanol. However, very few studies have used high-ionic-strength solutions because the aggregation and sedimentation of nanoparticles cause a stability problem. In this study, a stable water-based alumina nanofluid was prepared using stirred bead milling and exhibits a high electrical conductivity of 2420μS/cm at 23°C and excellent stability after five severe freezing–melting cycles. We then developed a process for mixing the water-based nanofluid with a high-ionic-strength potassium ferro/ferricyanide electrolyte and sodium dodecyl sulfate by using stirred bead milling and ultrasonication, thus forming a stable electrolyte-based nanofluid. According to the rotating disk electrode study, the electrolyte-based alumina nanofluid exhibits an unusual increase in the limiting current at high angular velocities, resulting from a combination of local percolation behavior and shear-induced diffusion. The electrolyte-based alumina nanofluid was demonstrated in a possible thermogalvanic application, since it is considered to be an alternative electrolyte for thermal energy harvesters because of the increased electrical conductivity and confined value of thermal conductivity.

Effect of particle shape on suspension stability and thermal conductivities of water-based bohemite alumina nanofluids

The suspension stability and thermal conductivity of water-based bohemite alumina nanofluids created using nanoparticles of various shapes (brick, platelet, and blade) at concentrations from 0.3 vol% to 7.0 vol% were theoretically and experimentally investigated. To quantitatively examine the effect of nanoparticle shape on suspension stability, this study uses the laser-scattering method rather than the zeta-potential measurement or the sedimentation test because both the zeta-potential and sedimentation tests cannot systematically represent the suspension stability of nanofluids. Using the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory, we explain why the suspension stability varies with nanoparticle shape despite similar volume fraction of nanoparticles, pH, and temperature. The thermal conductivities are also measured by the transient hot wire method, which was developed in house. Experimental data are compared with theoretical results predicted by the Hamilton–Crosser model, which considers the effect of nanoparticle shape. It is shown that the model cannot predict nanofluids thermal conductivity relative to nanoparticle shape. Finally it is clearly shown that the thermal conductivity of nanofluids strongly depends on the suspension stability of bohemite alumina with various shapes.

Experimental Investigation on the Thermal and Hydraulic Performance of Alumina–Water Nanofluids in Single-Phase Liquid-Cooled Cold Plates

The thermal and hydraulic performance of single-phase water-based alumina nanofluids used as coolants in liquid-cooled cold plates are reported and results baselined against those using water. Experimental results show that the heat transfer coefficient of the nanofluids increases with increasing particle loading at a fixed Reynolds number. When compared on the basis of a fixed volumetric coolant flowrate, pressure drop, and pumping power, however, no significant enhancements were observed using dilute (2%, 4%, and 6% volume fraction) alumina–water nanofluids (having an average diameter of 50 nm). In some cases, the thermal performance using nanofluids deteriorated. These results suggest that water-based alumina nanofluids do not offer a significant benefit for single-phase cooling in cold plates for the alumina nanofluids tested; yet, there remains an opportunity to identify nanoparticles—base fluid combinations that may improve performance with suggestions made herein. It should also be noted that the results reported in this study have been obtained at different degrees of dilution of a given alumina–water nanofluid having an average particle size of 50 nm.

Numerical study of natural convection in a horizontal cylinder filled with water-based alumina nanofluid.

Natural heat convection of water-based alumina (Al2O3/water) nanofluids (with volume fraction 1% and 4%) in a horizontal cylinder is numerically investigated. The whole three-dimensional computational fluid dynamics (CFD) procedure is performed in a completely open-source way. Blender, enGrid, OpenFOAM and ParaView are employed for geometry creation, mesh generation, case simulation and post process, respectively. Original solver ‘buoyantBoussinesqSimpleFoam’ is selected for the present study, and a temperature-dependent solver ‘buoyantBoussinesqSimpleTDFoam’ is developed to ensure the simulation is more realistic. The two solvers are used for same cases and compared to corresponding experimental results. The flow regime in these cases is laminar (Reynolds number is 150) and the Rayleigh number range is 0.7 × 107 ~ 5 × 107. By comparison, the average natural Nusselt numbers of water and Al2O3/water nanofluids are found to increase with the Rayleigh number. At the same Rayleigh number, the Nusselt number is found to decrease with nanofluid volume fraction. The temperature-dependent solver is found better for water and 1% Al2O3/water nanofluid cases, while the original solver is better for 4% Al2O3/water nanofluid cases. Furthermore, due to strong three-dimensional flow features in the horizontal cylinder, three-dimensional CFD simulation is recommended instead of two-dimensional simplifications.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0847-x) contains supplementary material, which is available to authorized users.

Experimental Investigation of Coupling Effects between Particle Size and Temperature on the Thermal Conductivity of Alumina Nanofluids

Abstract This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement ofwater-based alumina (Al 2 O 3 ) nanofluids, using the centrifuging method and relative centrifugal forces of differing magni-tude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined thecoupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the aluminananofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependenton nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwellmodel and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since theycannot account for the temperature- and size-dependent nature of water-based alumina nanofluids. Nomenclature a K : Kapitza radius [m]a p : Radius of particle [m]d : Mean particle diameter [m]d

Rheological behaviour and the hysteresis phenomenon of Al2O3 nanofluids

The effects of temperature and low-volume concentration on the dynamic viscosity of the Al2O3/water and Al2O3/ethylene glycol/water nanofluids are investigated. Nanofluids were prepared and characterised. Data were collected for temperatures ranging from 25 to 80°C. The presence of aggregated Al2O3 nanoparticles in the fluid, with average diameter of 109 nm which is ∼8 times the primary diameter (13 nm) of Al2O3 nanoparticles was witnessed. Furthermore, only at temperature below 40°C water-based alumina nanofluid at 0·05% v/v showed Newtonian behaviour. On the other hand, Al2O3/ethylene glycol/water mixture exhibited Newtonian behaviour. Results clearly showed the presence of a critical temperature, beyond which the particle suspension properties were noticed to be radically changed, which results in activating the hysteresis phenomenon. The hysteresis phenomenon on viscosity measurement, which is believed to be the first observed for ethylene glycol/water-based nanofluids, has raised serious concerns regarding the use of nanofluids for heat transfer enhancement.