Alumina Nanoparticles In Water Research Articles

A review of nucleate pool-boiling heat transfer in different liquids and nanofluids

The goal of this review is to examine the current state of the art in nucleate pool boiling heat transfer in a variety of different fluids. The review is divided into many sections that discuss heat transfer in pool boiling, such as pool boiling of nanofluids, boiling behavior of water–glycerin combinations, and operational parameters. With the appropriate mixes of hydrocarbons and other commercial liquids, higher heat transfer coefficients may be produced. Coatings of nanoparticles with varying layer thicknesses applied to the heater surface may be optimized to improve heat transfer from the pool to the surrounding water. The heat transfer hypothesis elucidates the peculiarities of each pool’s boiling regime. It is also possible to expand it to flow boiling by combining pool boiling liquid motion with external mechanical force. Other phase transitions, such as condensation, solidification, and melting, can also be described using boiling heat flow processes. Pool boiling performance can be improved by making a variety of adjustments to the heating surfaces as well as by using pure liquids in the water. Improvements can be made to boiling parameters such as the heat flux, the critical heat flux, the heat transfer coefficient, bubble development and departure, and so forth. A nanoparticle addition to a pure liquid or a surface coating on a heating surface can improve heat transfer and boiling properties by increasing the surface area of the liquid. Pool boiling critical heat flux was enhanced with Al2O3-water nano fluid. Authors used three different powder sizes of Al2O3 which were 0.05, 0.3 and 1.0 μm. Addition of alumina particle in water increases the boiling heat flux. Critical heat flux (CHF) was significantly enhanced using Titania and Alumina nano particles in water as compared to pure water. Average size of nano particle used was 85 nm measured by scattering electron microscope. Enhancement in Critical heat flux is due to nano particle coating on heating surface. Characteristics of nucleate boiling are greatly affected by the operating pressure. Miniature flat heat pipe (MFHP) with evaporator having micro grooved heat transfer surface gives 50% increment in critical heat flux at atmosphere pressure whereas this value increases up to 150% at 7.4 kPa pressure. The addition of CNT (carbon nanotube) to the base liquid increases the critical heat flux. Transmission electron microscopy confirms the average size of a nanoparticle as 15 nm. Authors found that by decreasing pressure from atmosphere condition critical heat flux increases to 200% with CNT/water nano fluid as compared to deionized water. SiC-water nanofluids of 100 nm size were experimented with at volume concentrations of 0.001%, 0.001%, and 0.01%. The size of the nanoparticle was confirmed by a scattering electron microscope. Authors concluded that at 0.01% of nano particle enhances critical heat flux to 105%.

Effects of fractional derivative and heat source/sink on MHD free convection flow of nanofluids in a vertical cylinder: A generalized Fourier's law model

This research looked at the unsteady free convection flows of an incompressible viscous fluid with heat/sink in a vertical cylinder containing a mixture of 47 nm alumina nanoparticles in water. The flow direction is subjected to a perpendicular magnetic field. The generalization entails taking into account a new version of the constitutive equation for thermal flux, known as the generalized Atangana-Baleanu derivative, which is based on the generalized time-fractional derivative with Mittag-Leffler kernel. Using the Laplace transform and the finite Hankel transform, closed forms of analytical solutions for temperature and velocity fields, represented with Bessel and generalized G–function of Lorenzo and Hartley functions, are determined. The generalized solutions are appropriate for particularizations to yield solutions corresponding to fractional derivatives with power-law kernel and exponential kernel. The Mittag-Leffler function is a one-parametric function. It is also possible to acquire the usual situation, which corresponds to classical Fourier's law. To compare models based on generalized Atangana-Baleanu, Atangana-Baleanu, Caputo, and Caputo-Fabrizio time fractional derivatives, numerical simulations produced with the program Mathcad are carried out and visually depicted.

Nanofluid application for heat transfer, safety, and natural circulation enhancement in the NuScale nuclear reactor as a small modular reactor using computational fluid dynamic (CFD) modeling via neutronic and thermal-hydraulics coupling

In recent years, “Nanofluid” and “Energy-Efficient Cooling” have been achieved growing attention for use in new nuclear reactor technology. Also, the assurance of reactor safety has become of top priority in nuclear energy development because of the significant role of nuclear power in providing worldwide electricity. The use of nanofluid coolant is an effective way to enhance safety margins and heat transfer performance. Studies also prove that nanofluids are promising cooling fluids for applying as a future coolant in nuclear reactors. The current paper investigates the nanofluid effects as a coolant on the velocity of bulk, pressure drop, heat transfer coefficient, power peaking factors, and minimum departure from nucleate boiling ratio in a NuScale reactor, a natural circulation pressurized water reactor (PWR). It also analyzes the thermal characteristics of Al2O3 nanofluid with specific attention to their boiling heat transfer behavior. The study first presents the NuScale designed core with the use of water and different concentrations of Al2O3 nanofluid (0.001–10% volume fractions and 10–90 nm particle sizes). Then it shows the simulated equivalent cell with surrounding coolant utilizing computational fluid dynamic code (CFD). The study also describes the outcomes of replacing water with nanofluid coolant on natural circulation parameters, heat transfer coefficient, and minimum departure from nucleate boiling ratio with changes in nanoparticle concentrations and sizes. The results demonstrate the potential of this innovative coolant to enhance the minimum departure from nucleate boiling ratio and heat transfer coefficient. Overall, the presence of Alumina nanoparticles in water improves thermal performance and safety. The investigation also shows that the nanoparticles do not change the power peaking factor and neutronic performance significantly.

Experimental Thermal Conductivity of Alumina Nanoparticles in Water With and Without Sonication

Experimental thermal conductivity of alumina nanoparticles in water is measured with the transient thermal probe, in the presence of sonication (i.e., with ultrasounds), or not. We investigate two types of alumina particles, with the diameter equal to 7 nm and 50 nm. The experimental results, with and without sonication, show that the effective thermal conductivity is greater for the alumina nanoparticle with the smaller diameter. The effective thermal conductivity is greater in the presence of sonication, with a larger relative increase for the smaller diameter nanofluid. We compare the present experimental thermal conductivity with the empirical/theoretical prediction models of the literature with a reasonable good agreement.

Küppers–Lortz instability in rotating Rayleigh–Bénard convection bounded by rigid/free isothermal boundaries

• Manifestation of Küppers–Lortz instability in nanoliquids is investigated. • Experimental boundary condition is considered. • The effect of nanoparticles in water is to promote rolls. • Küppers–Lortz instability is inhibited by nanoparticles. • The results are validated by comparing with limiting cases. Manifestation of Küppers–Lortz secondary instability in rotating Rayleigh–Bénard convection in a Newtonian liquid (water) and in homogeneous and heterogeneous nanoliquids is reported for rigid-isothermal and free-isothermal boundaries. Water–alumina and water–alumina–copper are used as representative homogeneous and heterogeneous nanoliquids. Experimental data on thermal conductivity and dynamic viscosity are used and empirical models which represent experimental data faithfully are obtained. In order to study Küppers–Lortz secondary instability an energy-conserving, ninth-order Lorenz model is derived using the minimal mode truncated Fourier–Galerkin expansion. It is shown that the critical Rayleigh number obtained in the case of rotating Rayleigh–Bénard convection in water–alumina–copper and water–alumina nanoliquids is smaller than the value obtained in the case of water, whereas the critical Taylor number obtained in the case of water–alumina–copper and water–alumina nanoliquids is larger than the value obtained in the case of water. Thus, the individual effect of suspending dilute concentrations of homogeneous and heterogeneous nanoparticles in water is to promote formation of the steady, primary instability (longitudinal rolls) and impede the appearance of the Küppers–Lortz instability (intersecting rolls). It is also shown that compared to a homogeneous nanoliquid, a heterogeneous nanoliquid is more pro-primary-instability as well as anti-secondary-instability. Further, it is found that by slightly increasing the volume fraction of alumina nanoparticles in water one can achieve the same effect as that of alumina and copper in water. In order to validate the results on Küppers–Lortz instability, we considered the results on Küppers–Lortz instability in the absence of nanoparticles obtained in the two cases of rigid and free boundaries and compared them with those of previous investigations, and reasonably good agreement is found.

Direct Visualization of the Hydration Layer on Alumina Nanoparticles with the Fluid Cell STEM in situ.

Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions. We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. Our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles.

Critical heat flux enhancement in pool boiling using alumina nanofluids

AbstractThe pool boiling characteristics of dilute dispersions of alumina nanoparticles in water were studied. Consistent with other nanofluid studies, it was found that a significant enhancement in critical heat flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). During experimentation and subsequent inspection, formation of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly changes surface texture of the heater wire surface which could be the reason for improvement in the CHF value. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20301

Nuclear magnetic resonance-based study of ordered layering on the surface of alumina nanoparticles in water

Layering of water molecules on the surface of alumina nanoparticles in an alumina/water nanofluid is studied using nuclear magnetic resonance (NMR). The data suggest that a thin ordered layer (∼1.4 nm) of water molecules surrounds each nanoparticle. This ordered layer increases the nanoparticle effective volumetric fraction; however, the nanofluid thermal conductivity appears to be unaffected by this layer, and in good agreement with Maxwell’s effective medium theory. Furthermore, the NMR data suggest that the nanoparticles do not enhance, but rather stifle micromixing in the base fluid.

An experimental investigation of forced convective cooling performance of a microchannel heat sink with Al 2O 3/water nanofluid

Experiments were conducted to investigate forced convective cooling performance of a copper microchannel heat sink with Al 2O 3/water nanofluid as the coolant. The microchannel heat sink fabricated consists of 25 parallel rectangular microchannels of length 50 mm with a cross-sectional area of 283 μm in width by 800 μm in height for each microchannel. Hydraulic and thermal performances of the nanofluid-cooled microchannel heat sink have been assessed from the results obtained for the friction factor, the pumping power, the averaged heat transfer coefficient, the thermal resistance, and the maximum wall temperature, with the Reynolds number ranging from 226 to 1676. Results show that the nanofluid-cooled heat sink outperforms the water-cooled one, having significantly higher average heat transfer coefficient and thereby markedly lower thermal resistance and wall temperature at high pumping power, in particular. Despite the marked increase in dynamic viscosity due to dispersing the alumina nanoparticles in water, the friction factor for the nanofluid-cooled heat sink was found slightly increased only.

The effect of particle size on the thermal conductivity of alumina nanofluids

We present new data for the thermal conductivity enhancement in seven nanofluids containing 8–282 nm diameter alumina nanoparticles in water or ethylene glycol. Our results show that the thermal conductivity enhancement in these nanofluids decreases as the particle size decreases below about 50 nm. This finding is consistent with a decrease in the thermal conductivity of alumina nanoparticles with decreasing particle size, which can be attributed to phonon scattering at the solid–liquid interface. The limiting value of the enhancement for nanofluids containing large particles is greater than that predicted by the Maxwell equation, but is predicted well by the volume fraction weighted geometric mean of the bulk thermal conductivities of the solid and liquid. This observation was used to develop a simple relationship for the thermal conductivity of alumina nanofluids in both water and ethylene glycol.

Transport properties of alumina nanofluids

Recent studies have showed that nanofluids have significantly greater thermal conductivitycompared to their base fluids. Large surface area to volume ratio and certain effects ofBrownian motion of nanoparticles are believed to be the main factors for the significantincrease in the thermal conductivity of nanofluids. In this paper all three transportproperties, namely thermal conductivity, electrical conductivity and viscosity, were studiedfor alumina nanofluid (aluminum oxide nanoparticles in water). Experiments wereperformed both as a function of volumetric concentration (3–8%) and temperature(2–50 °C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. Theeffect of particle size was not studied. The transient hot wire method as describedby Nagaska and Nagashima for electrically conducting fluids was used to testthe thermal conductivity. In this work, an insulated platinum wire of 0.003 inchdiameter was used. Initial calibration was performed using de-ionized water andthe resulting data was within 2.5% of standard thermal conductivity values forwater. The thermal conductivity of alumina nanofluid increased with bothincrease in temperature and concentration. A maximum thermal conductivity of0.7351 W m−1 K−1 was recorded for an 8.47% volume concentration of alumina nanoparticles at46.6 °C. The effective thermal conductivity at this concentration and temperature was observed tobe 1.1501, which translates to an increase in thermal conductivity by 22% when comparedto water at room temperature. Alumina being a good conductor of electricity, aluminananofluid displays an increasing trend in electrical conductivity as volumetric concentrationincreases. A microprocessor-based conductivity/TDS meter was used to perform theelectrical conductivity experiments. After carefully calibrating the conductivitymeter’s glass probe with platinum tip, using a standard potassium chloride solution,readings were taken at various volumetric concentrations. A 3457.1% increase in theelectrical conductivity was measured for a small 1.44% volumetric concentrationof alumina nanoparticles in water. The highest value of electrical conductivity,314 µS cm−1, was recorded for a volumetric concentration of 8.47%. In the determination of thekinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constanttemperature bath was used. Calibrated capillary viscometers were used to measure flowunder gravity at precisely controlled temperatures. The capillary viscometers werecalibrated with de-ionized water at different temperatures, and the resulting kinematicviscosity values were found to be within 3% of the standard published values. An increaseof 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration ofalumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid,2.901 42 mm2 s−1, wasobtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles. The experimentalresults of the present work will help researchers arrive at better theoretical models.

A sedimentation study to optimize the dispersion of alumina nanoparticles in water

Sedimentation studies have been carried out to optimize the dispersion conditions of aqueous alumina nanopowder suspensions with or without dispersants (ammonium salt of polymethacrylic acid or rhamnolipids at 15%). Different dispersant dosages, solid loadings, pulp densities and pH values were examined. The iso-electric point (IEP) of the alumina nanopowder was found to be pHiep= 9.2. The experiments revealed that the polymethacrylic acid was more effective as dispersant than rhamnolipids in a wide range of pH at all solid-loading conditions tested. Optimum dispersant dosages for polymethacrylic acid and rhamnolipids to achieve maximum stability of alumina nanodispersion at iso-electric point were found to be 9.25 mg/g and 57.75 mg/g solids, respectively.