Non-isobaric Marangoni boundary layer flow for Cu,Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and TiO<Subscript>2</Subscript> nanoparticles in a water based fluid

In this paper, a non-isobaric Marangoni boundary layer flow that can be formed along the interface of immiscible nanofluids in surface driven flows due to an imposed temperature gradient, is considered. The solution is determined using a similarity solution for both the momentum and energy equations and assuming developing boundary layer flow along the interface of the immiscible nanofluids. The resulting system of nonlinear ordinary differential equations is solved numerically using the shooting method along with the Runge-Kutta-Fehlberg method. Numerical results are obtained for the interface velocity, the surface temperature gradient as well as the velocity and temperature profiles for some values of the governing parameters, namely the nanoparticle volume fraction φ (0≤φ≤0.2) and the constant exponent β. Three different types of nanoparticles, namely Cu, Al₂O₃ and TiO₂ are considered by using water-based fluid with Prandtl number Pr =6.2. It was found that nanoparticles with low thermal conductivity, TiO₂, have better enhancement on heat transfer compared to Al₂O₃ and Cu. The results also indicate that dual solutions exist when β<0.5. The paper complements also the work by Golia and Viviani (Meccanica 21:200–204, 1986) concerning the dual solutions in the case of adverse pressure gradient.     

Numerical investigation of natural convection of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanofluid in vertical annuli

This paper presents the numerical study of internal free convection of Al₂O₃ water nanofluid in vertical annuli. Vertical walls are maintained at constant temperatures and horizontal walls are adiabatic. Results are validated by experimental data. Effect of nanofluids on natural convection is investigated as a function of geometrical and physical parameters and particle fractions for aspect ratio of 1 ≤ H/L ≤ 5, Grashof number of 10³ ≤ Gr ≤ 10⁵ and concentration of 0 ≤ ϕ ≤ 0.06. More than 330 different numerical cases are investigated to develop a new correlation for the Nusselt number. This correlation is presented as a function of Nusselt number of base fluid and particle fraction which is a linear decreasing function of particle fraction. The developed correlation for annuli is also valid for the natural convection of Al₂O₃ water nanofluid in a square cavity. Furthermore, the effect of the viscosity and conductivity models on the Nusselt number of nanofluids in cylindrical cavities are discussed.     

Electrorheological response of SnO<Subscript>2</Subscript> and Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in silicon oil

The electrorheological properties (ER) of some fluids containing particles change extensively under the external electrical field. This phenomenon is applicable in many industries and equipments, such as clutches and motor driven rotor, which would transfer the spin to a drive shaft through a thin layer of electrorheological fluid. In this investigation, the effects of external electrical field on ER properties of non-Newtonian fluids (silicon oil) with the addition of SnO₂ and Y₂O₃ nanoparticles were studied. The ER properties were measured for a wide range of SnO₂ and Y₂O₃ nanoparticle concentrations and DC electrical voltages using concentric cylinder rotary rheometer. Based on the results, ER properties of nanofluids, e.g., apparent viscosity, shear stress, and yield stress, were enhanced by applying electrical field and increasing SnO₂ and Y₂O₃ concentrations.

Pool boiling heat transfer performance of Newtonian nanofluids

Experimental measurements were carried out on the boiling heat transfer characteristics of γ-Al₂O₃/water and SnO₂/water Newtonian nanofluids. Nanofluids are liquid suspensions containing nanoparticles with sizes smaller than 100 nm. In this research, suspensions with different concentrations of γ-Al₂O₃ and SnO₂ nanoparticles in water were studied under nucleate pool boiling heat transfer conditions. Results show that nanofluids possess noticeably higher boiling heat transfer coefficients than the base fluid. The boiling heat transfer coefficients depend on the type and concentration of nanoparticles.     

CFD studies on natural convection heat transfer of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-water nanofluids

This work is focused on numerical simulations of natural convection heat transfer in Al₂O₃-water nanofluids using computational fluid dynamics approach. Fluent v6.3 is used to simulate water based nanofluid considering it as a single phase. Thermo-physical properties of the nanofluids are considered in terms of volume fraction and size of nanoparticles, size of base fluid molecule and temperature. The numerical values of effective thermal conductivity have also been compared with the experimental values available in the literature. The numerical result simulated shows decrease in heat transfer with increase in particle volume fraction. Computed result shows similar trend in increase of Nusselt number with Relayigh number as depicted by experimental results. Streamlines and temperature profiles are plotted to demonstrate the effect.     

Numerical study of conjugate heat transfer in rectangular microchannel heat sink with Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/H<Subscript>2</Subscript>O nanofluid

In the present paper, conjugate heat transfer approach has been used to numerically study laminar forced convective heat transfer characteristics of Al₂O₃/H₂O nanofluid flowing in a silicon microchannel heat sink (MCHS) of rectangular cross-section using thermal dispersion model. Results are presented in terms of thermal resistance that characterizes MCHS performance. It is observed that use of nanofluid improves MCHS performance by reducing fin (conductive) thermal resistance.     

Production of nanomaterials by vaporizing ceramic targets irradiated by a moderate-power continuous-wave CO<Subscript>2</Subscript> laser

The efficiency of utilization of CO ₂ laser energy for vaporization of Al ₂ O ₃ ceramics is evaluated using a mathematical model for the interaction of laser radiation with materials. It is shown that the calculated efficiency of radiation-energy utilization is not higher than 15% at a radiation power density of 10⁵ W/cm ² on the target. On the experimental facility designed for the synthesis of nanopowders, a vaporization rate of 1 g/h was achieved for Al ₂ O ₃, which corresponds to a 3% efficiency of radiation-energy utilization. The dependence of the characteristic particle size of a zirconium oxide nanopowder on helium pressure in the range of 0.01–1.00 atm was studied. Results of experiments on vaporization of multicomponent materials (LaNiO ₃ and the Tsarev meteorite) are given. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 172–184, March–April, 2007.     

Properties of an Al/(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>+TiB<Subscript>2</Subscript>+ZrB<Subscript>2</Subscript>) hybrid composite manufactured by powder metallurgy and hot pressing

The properties and microstructure of an Al/(Al₂O₃ + TiB₂ + ZrB₂) hybrid composite made by using hot pressing of aluminum combined with different amounts of TiB₂, ZrB₂, and Al₂O₃ powders are studied. The mechanical properties of the composites are investigated on the basis of microhardness and compression tests. The results show that the microstructure of the composites is uniform and the particles are well distributed in the matrix.     

Using waste to treat waste: Red mud induced hierarchical porous γ-AlOOH and γ-Al2O3 microspheres as superior Pd support for catalytic reduction of 4-nitrophenol

Toward the imperative treatment of the industrial wastewater containing 4-nitrophenol (4-NP) and industrial solid waste red mud (RM), an innovative approach of “Using waste to treat waste” is developed. Valuable element Al is leached from the RM first, the resultant NaAlO₂ solution is hydrothermally converted to γ-AlOOH hierarchical porous microspheres (RM γ-AlOOH HPMSs, average diameter: 2.0 μm, S_BET: 77.81 m² g⁻¹, pore volume: 0.38 cm³ g⁻¹) in the presence of urea. The subsequent mild thermal conversion results in γ-Al₂O₃ hierarchical porous microspheres (RM γ-Al₂O₃ HPMSs). Both of the RM γ-AlOOH and RM γ-Al₂O₃ HPMSs are employed as the Pd catalyst support for the catalytic reduction of 4-NP. Particularly, the as-obtained composite Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ exhibit excellent catalytic activities with superior k_nor as 8204.5 and 4831.4 s⁻¹ g⁻¹, respectively, significantly higher than that of most Pd based catalysts. Moreover, the excellent catalytic stability and durability of the Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ within 10 successive cycles of reduction enable the present industrial solid waste RM induced γ-AlOOH and γ-Al₂O₃ HPMSs as great promising Pd catalyst support for the reduction of the industrial wastewater containing 4-NP.     

Impact of CO<Subscript>2</Subscript> Injection on Flow Behavior of Coalbed Methane Reservoirs

On the basis of observations at four enhanced coalbed methane (ECBM)/CO₂ sequestration pilots, a laboratory-scale study was conducted to understand the flow behavior of coal in a methane/CO₂ environment. Sorption-induced volumetric strain was first measured by flooding fresh coal samples with adsorptive gases (methane and CO₂). In order to replicate the CO₂–ECBM process, CO₂ was then injected into a methane-saturated core to measure the incremental “swelling.” As a separate effort, the permeability of a coal core, held under triaxial stress, was measured using methane. This was followed by CO₂ flooding to replace the methane. In order to best replicate the conditions in situ, the core was held under uniaxial strain, that is, no horizontal strain was permitted during CO₂ flooding. Instead, the horizontal stress was adjusted to ensure zero strain. The results showed that the relative strain ratio for CO₂/methane was between 2 and 3.5. The measured volumetric strains were also fitted using a Langmuir-type model, thus enabling calculation of the strain at any gas pressure and using the analytical permeability models. For permeability work, effort was made to increase the horizontal stress to achieve the desired zero horizontal strain condition expected under in situ condition, but this became impossible because the “excess” stress required to maintain this condition was very large, resulting in sample failure. Finally, when CO₂ was introduced and horizontal strain was permitted, permeability reduction was an order of magnitude greater, suggesting that the “excess” stress would have reduced it significantly further. The positive finding of the work was that the “excess” stresses associated with injection of CO₂ are large. The excess stresses generated might be sufficient to cause microfracturing and increased permeability, and improved injectivity. Also, there might be a weakening effect resulting from repeated CO₂ injection, as has been found to be the case with thermal cycling of rocks.     

Laminar convective heat transfer of non-Newtonian nanofluids with constant wall temperature

Nanofluids are obtained by dispersing homogeneously nanoparticles into a base fluid. Nanofluids often exhibit higher heat transfer rate in comparison with the base fluid. In the present study, forced convection heat transfer under laminar flow conditions was investigated experimentally for three types of non-Newtonian nanofluids in a circular tube with constant wall temperature. CMC solution was used as the base fluid and γ-Al₂O₃, TiO₂ and CuO nanoparticles were homogeneously dispersed to create nanodispersions of different concentrations. Nanofluids as well as the base fluid show shear thinning (pseudoplastic) rheological behavior. Results show that the presence of nanoparticles increases the convective heat transfer of the nanodispersions in comparison with the base fluid. The convective heat transfer enhancement is more significant when both the Peclet number and the nanoparticle concentration are increased. The increase in convective heat transfer is higher than the increase caused by the augmentation of the effective thermal conductivity.     

ℒ<Subscript>2</Subscript>–ℒ<Subscript>∞</Subscript> nonlinear system identification via recurrent neural networks

This paper proposes a new neural network ℋ_∞ synchronization (NNHS) scheme for unknown chaotic systems. In the proposed framework, a dynamic neural network is constructed as an alternative to approximate the chaotic system. Based on this neural network and linear matrix inequality (LMI) formulation, the NNHS controller and the learning law are presented to reduce the effect of disturbance to an ℋ_∞ norm constraint. It is shown that finding the NNHS controller and the learning law can be transformed into the LMI problem and solved using the convex optimization method. A numerical example is presented to demonstrate the validity of the proposed NNHS scheme.     

Modeling of Rocks and Cement Alteration due to CO<Subscript>2</Subscript> Injection in an Exploited Gas Reservoir

The injection of CO₂ in exploited natural gas reservoirs as a means to reduce greenhouse gas (GHG) emissions is highly attractive as it takes place in well-known geological structures of proven integrity with respect to gas leakage. The injection of a reactive gas such as CO₂ puts emphasis on the possible alteration of reservoir and caprock formations and especially of the wells’ cement sheaths induced by the modification of chemical equilibria. Such studies are important for injectivity assurance, wellbore integrity, and risk assessment required for CO₂ sequestration site qualification. Within a R&D project funded by Eni, we set up a numerical model to investigate the rock–cement alterations driven by the injection of CO₂ into a depleted sweet natural gas pool. The simulations are performed with the TOUGHREACT simulator (Xu et al. in Comput Geosci 32:145–165, 2006) coupled to the TMGAS EOS module (Battistelli and Marcolini in Int J Greenh Gas Control 3:481–493, 2009) developed for the TOUGH2 family of reservoir simulators (Pruess et al. in TOUGH2 User’s Guide, Version 2.0, 1999). On the basis of field data, the system is considered in isothermal (50°C) and isobaric (128.5 bar) conditions. The effects of the evolving reservoir gas composition are taken into account before, during, and after CO₂ injection. Fully water-saturated conditions were assumed for the cement sheath and caprock domains. The gas phase does not flow by advection from the reservoir into the interacting domains so that molecular diffusion in the aqueous phase is the most important process controlling the mass transport occurring in the system under study.     

Pore Scale Modeling of Reactive Transport Involved in Geologic CO<Subscript>2</Subscript> Sequestration

We apply a multi-component reactive transport lattice Boltzmann model developed in previous studies for modeling the injection of a CO₂-saturated brine into various porous media structures at temperatures T = 25 and 80°C. In the various cases considered the porous medium consists initially of calcite with varying grain size and shape. A chemical system consisting of Na⁺, Ca²⁺, Mg²⁺, H⁺, CO₂^°(aq){{\rm CO}_2^{\circ}{\rm (aq)}}, and Cl⁻ is considered. Flow and transport by advection and diffusion of aqueous species, combined with homogeneous reactions occurring in the bulk fluid, as well as the dissolution of calcite and precipitation of dolomite are simulated at the pore scale. The effects of the structure of the porous media on reactive transport are investigated. The results are compared with a continuum-scale model and the discrepancies between the pore- and continuum-scale models are discussed. This study sheds some light on the fundamental physics occurring at the pore scale for reactive transport involved in geologic CO₂ sequestration.     

Experimental investigations and theoretical determination of thermal conductivity and viscosity of Al2O3/water nanofluid

Experimental investigations and theoretical determination of effective thermal conductivity and viscosity of Al₂O₃/H₂O nanofluid are reported in this paper. The nanofluid was prepared by synthesizing Al₂O₃ nanoparticles using microwave assisted chemical precipitation method, and then dispersing them in distilled water using a sonicator. Al₂O₃/water nanofluid with a nominal diameter of 43 nm at different volume concentrations (0.33–5%) at room temperature were used for the investigation. The thermal conductivity and viscosity of nanofluids are measured and it is found that the viscosity increase is substantially higher than the increase in thermal conductivity. Both the thermal conductivity and viscosity of nanofluids increase with the nanoparticle volume concentration. Theoretical models are developed to predict thermal conductivity and viscosity of nanofluids without resorting to the well established Maxwell and Einstein models, respectively. The proposed models show reasonably good agreement with our experimental results.     

Initiation of Combustion in a Supersonic Hydrogen-Air Mixture Flow by CO<Subscript>2</Subscript>-Laser Radiation

Features of the ignition kinetics of an H₂/air mixture in the supersonic flow behind an inclined shock front are analyzed when asymmetric vibrations of a small amount (<1%) of O₃ molecules specially introduced into the initial mixture are excited by 9.7 μm wavelength radiation. It is shown that this radiation leads to intensification of the chain reactions and makes it possible to organize combustion at small distances from the front (of the order of 1 m) of even relatively weak shocks at small values of the laser radiation energies absorbed by the gas. This method of initiating combustion in a supersonic flow is 10–100 times more efficient than the thermal method.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 157–167.Original Russian Text Copyright © 2005 by Lukhovitskii, Starik, and Titova.     

On the thermal buckling of simply supported rectangular plates made of a sigmoid functionally graded Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> based material

We study the thermal buckling of a simply supported sigmoid functionally graded (SFGM) rectangular plate using first-order shear deformation theory. The S-FGM system consists of ceramic (Al₂O₃) and metal (Al) phases varying across the plate thickness according to a law described by two power-law functions. The effective properties of the composite are determined by the rule of mixtures, whose implementation is simpler than that of methods of micromechanics. The thermal heating is characterized by a uniform, linear, or sinusoidal temperature distribution across the plate thickness. The effects of the plate aspect ratio, the relative thickness, the gradient index, and the transverse shear on the buckling temperature difference are studied.     

An experimental—Numerical evaluation of the<Emphasis Type="Italic">T</Emphasis><Stack><Subscript>ε</Subscript><Superscript>*</Superscript></Stack> integral for a three-dimensional crack front

TheT _ε ^* integral was calculated on the surface of single edge notched, three-point bend (SE(B)) specimens using experimentally obtained displacements. Comparison was made withT _ε ^* calculated with the measured surface displacements andT _ε ^* calculated at several points through the thickness of a finite element (FE) model of the SE(B) specimen. Good comparison was found between the surfaceT _ε ^* calculated from displacements extracted from the FE model and the surfaceT _ε ^* calculated from experimentally obtained displacements. The computedT _ε ^* integral was also observed to decrease as the crack front was traversed from the surface to the mid-plane of the specimen. Mid-planeT _ε ^* values tend to be approximately 10% of the surface values.     

Influence of thermophysical properties on the thermal stability of insulated composite superconducting tape

The effect of thermal conductivity and heat capacity on thermal stability of Nb-Ti tape superconductor stabilized with copper and subjected to transient thermal disturbance, was numerically investigated. The problem was solved by using the three- dimensional heat conduction equation. The results show that the anisotropy of thermophysical properties of the superconductor have significant effect on the thermal stability. It is found that the thermal stability of the tape is improved by increasing the heat capacity and decreasing the thermal conductivity. The best limits for anisotrpy factors α _k and α _c are (1.0; 1.5) and (2.0; 2.5), respectively.     

STREAMLINE-BASED MATHEMATICAL MODEL FOR CO2 MISCIBLE FLOODING

According to the research theory of improved black oil simulator, a practical mathematical model for C02 miscible flooding was presented. In the model, the miscible process simulation was realized by adjusting oil/gas relative permeability and effective viscosity under the condition of miscible flow. In order to predict the production performance fast, streamline method is employed to solve this model as an alternative to traditional finite difference methods. Based on streamline distribution of steady-state flow through porous media with complex boundary confirmed with the boundary element method (BEM), an explicit total variation diminishing (TVD) method is used to solve the one-dimensional flow problem. At the same time, influences of development scheme, solvent slug size, and injection periods on CO2 drive recovery are discussed. The model has the advantages of less information need, fast calculation, and adaptation to calculate CO2 drive performance of all kinds of patterns in a random shaped porous media with assembly boundary. It can be an effective tool for early stage screening andmiscible oil field.reservoir dynamic management of the CO2 miscible oil field.