MHD squeezed flow of water functionalized metallic nanoparticles over a sensor surface

Present study is devoted to analyze the magnetohydrodynamics (MHD) squeezed flow of nanofluid over a sensor surface. Modeling of the problem is based on the geometry and the interaction of three different kinds of metallic nanoparticles namely: copper (Cu), alumina (Al₂O₃) and titanium dioxide (TiO₂) with the homogeneous mixture of base fluid (water). The self-similar numerical solutions are presented for the reduced form of the system of coupled ordinary differential equations. The effects of nanoparticles volume friction, permeable velocity and squeezing parameter for the flow and heat transfer within the boundary layer are presented through graphs. Comparison among the solvent are constructed for both skin friction and Nusselt number. Flow behavior of the working nanofluid according to the present geometry has analyzed through Stream lines. Conclusion is drawn on the basis of entire investigation and it is found that in squeezing flow phenomena Cu–water gives the better heat transfer performance as compare with the rest of mixtures.     

Anisotropic slip magneto-bioconvection flow from a rotating cone to a nanofluid with Stefan blowing effects

A mathematical model for two dimensional steady laminar natural convective anisotropic slip boundary layer flows from a rotating vertical cone embedded in ethylene glycol bionanofluid is presented. The influence of Stefan blowing is also taken into account. Four different non-particles namely Copper (Cu), Alumina (Al₂O₃), Copper Oxide (Cuo), Titanium Oxide (TiO₂) are explored. Suitable similarity transformations are used to convert the governing equations into non-linear ordinary differential equations. These are then solved numerically, with appropriate boundary conditions, utilizing an implicit finite difference method (the BVP5C code in MATLAB). During computation Sc, Lb, Le and Lb are presented as unity, whilst $\mathrm{Pr}$ is taken as 151. The effects of the governing parameters on the dimensionless velocities, temperature, nanoparticle volume fraction, density of motile microorganisms as well as on the local skin friction, local Nusselt, Sherwood number and motile micro-organism number density are thoroughly examined via tables and graphs. It is found that the skin friction factor increases with tangential slip, magnetic field and Schmidt number whilst it decreases with blowing parameter and spin parameters. It is further observed that both the friction and heat transfer rates are highest for copper nanoparticles and lowest for TiO₂nanoparticles. Validation of the BVP5C numerical solutions with published results for several special cases of the general model is included. The study is relevant to electro-conductive bio-nano-materials processing.     

Hybrid nanofluid flow induced by an exponentially shrinking sheet

The flow and heat transfer induced by an exponentially shrinking sheet with hybrid nanoparticles is investigated in this paper. The alumina (Al₂O₃) and copper (Cu) nanoparticles are suspended in water to form Al₂O₃–Cu/water hybrid nanofluid. In addition, the effects of magnetohydrodynamic (MHD) and radiation are also taken into account. The similarity equations are gained from the governing equations using similarity transformation, and their solutions are obtained by the aid of the bvp4c solver available in Matlab software. Results elucidate that dual solutions exist for suction strength S > S_c and shrinking strength λ > λ_c. The critical values S_c and λ_c for the existence of the dual solutions decrease with the rising of the solid volume fractions of Cu, φ₂ and the magnetic parameter, M. Besides, the skin friction and the heat transfer rate increase with the increasing of φ₂ and M for the upper branch solutions. The increasing of radiation, R leads to reduce the surface temperature gradient which implies to the reduction of the heat transfer rate for both branches when λ < 0 (shrinking sheet). The stability of the dual solutions is determined by the temporal stability analysis, and it is discovered that only one of them is stable and physically applicable.     

方腔内Cu/Al2O3水混合纳米流体自然对流的格子Boltzmann模拟

纳米流体作为一种较高的导热介质, 广泛应用于各个传热领域. 鉴于纳米颗粒导热系数和成本之间的矛盾, 本文提出了一种混合纳米流体. 为了研究混合纳米流体颗粒间相互作用机理和自然对流换热特性, 在考虑颗粒间相互作用力的基础上, 利用多尺度技术推导了纳米流体流场和温度场的格子Boltzmann方程, 通过耦合流动和温度场的演化方程, 建立了Cu/Al₂O₃水混合纳米流体的格子Boltzmann模型, 研究了混合纳米流体颗粒间的相互作用机理和纳米颗粒在腔体内的分布. 发现在颗粒间相互作用力中, 布朗力远远大于其他作用力, 温差驱动力和布朗力对纳米颗粒的分布影响最大. 分析了纳米颗粒组分、瑞利数对自然对流换热的影响, 对比了混合纳米流体(Cu/Al₂O₃-水)与单一金属颗粒纳米流体(Al₂O₃-水)的自然对流换热特性, 发现混合纳米流体具有更强的换热特性.     

Heat transfer enhancement by application of nano-powder

In this investigation, laminar flow heat transfer enhancement in circular tube utilizing different nanofluids including Al₂O₃ (20 nm), CuO (50 nm), and Cu (25 nm) nanoparticles in water was studied. Constant wall temperature was used as thermal boundary condition. The results indicate enhancement of heat transfer with increasing nanoparticle concentrations, but an optimum concentration for each nanofluid suspension can be found. Based on the experimental results, metallic nanoparticles show better enhancement of heat transfer coefficient in comparison with oxide particles. The promotions of heat transfer due to utilizing nanoparticles are higher than the theoretical correlation prediction.     

Heat transfer behaviours of nanofluids in a uniformly heated tube

In the present work, we consider the problem of the forced convection flow of water– γAl₂O₃ and ethylene glycol– γAl₂O₃ nanofluids inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall. In general, it is observed that the inclusion of nanoparticles has increased considerably the heat transfer at the tube wall for both the laminar and turbulent regimes. Such improvement of heat transfer becomes more pronounced with the increase of the particle concentration. On the other hand, the presence of particles has produced adverse effects on the wall friction that also increases with the particle volume concentration. Results have also shown that the ethylene glycol– γAl₂O₃ mixture gives a far better heat transfer enhancement than the water– γAl₂O₃ mixture.     

Surface Plasmon Resonance of Au Nanoparticles Fabricated by Negative Ion Implantation and Grid Structure toward Plasmonic Applications

Optical properties of Au nanoparticle composites and a grid structure of Cu nanoparticle composite were studied. Negative ion implantation was applied to synthesize Au and Cu nanoparticles in amorphous SiO₂ and Al₂O₃. Au nanoparticles were embedded within a depth of 30 nm by 60keV Au⁻ implantation. The surface plasmon resonance (SPR) of Au:SiO₂ and Au: Al₂O₃ composites shifted to red and to blue, respectively, compared to calculated ones by the Mie theory. Optical nonlinearity was measured with pump-probe femtosecond spectroscopy and the transient spectrum of Au: Al₂O₃ composite presented a large red shift from the SPR peak. Image mapping of far-field transmitted intensity of Cu-implanted SiO₂ with a fine grid structure drawn by laser-lithography was observed by a scanning near-field optical microscopy (SNOM) system.     

The tribology properties of alumina/silica composite nanoparticles as lubricant additives

The as-prepared alumina/silica (Al₂O₃/SiO₂) composite nanoparticles were synthesized with a hydrothermal method and modified by silane coupling agent. The tribological properties of the modified Al₂O₃/SiO₂ composite nanoparticles as lubricating oil additives were investigated by four-ball and thrust-ring tests in terms of wear scar diameter, friction coefficient, and the morphology of thrust-ring. It is found that their anti-wear and anti-friction performances are better than those of pure Al₂O₃ or SiO₂ nanoparticles. When the optimized concentration of nanoparticle additive is 0.5 wt.%, the diameters of wear scar and friction coefficients are both smallest. Such modified composite nanoparticles can adsorb onto the friction surfaces, which results in rolling friction. Therefore, the friction coefficient is reduced.     

Influence of metallic nanoparticles in water driven along a wavy circular cylinder

In the present study, simultaneous effects of metallic nanoparticles and magnetohydrodynamic due to stagnation point flow of nanofluid along a wave circular cylinder is presented. The effect of induced magnetic field is incorporated to deal the boundary and thermal boundary layer domain. Mathematical modelling for momentum and energy equation is constructed that is based upon three different kinds of nanoparticles namely: copper (Cu), Titanium di oxide (TiO₂), and alumina (Al₂O₃) within the working fluid water. Each mixture is analysed at the individual level and made comparison amongst all the mixture to examine the resistance and thermal conductivity of nanofluid within the boundary layer region. The solutions are exposed via boundary value problem using shooting method along with the Runge-Kutta-Fehlberg method. The characteristics of emerging parameters for the fluid flow and heat transfer are discussed through graphs and tables. The effects of ϕ (nanoparticle volume fraction) on heat transfer and shear stress at the wall are analysed in detail. It is finally concluded that by increasing the ratio of nanoparticles there is a significant increase in the temperature but slight decrease in the velocity profile.     

亚纳米厚的氧化铝包裹层可以显著提高负载型金纳米颗粒催化剂的热稳定性

负载型金纳米颗粒催化剂在许多催化反应中展现出非常好的催化活性,但是金纳米颗粒在高温等反应条件下容易烧结团聚,极大地限制了金催化剂的应用。利用原子层沉积技术在Au/TiO₂催化剂表面分别精确沉积了一层超薄的二氧化钛和氧化铝包裹层,并对比研究了包裹层对金纳米颗粒的热稳定性影响。原位红外漫反射CO吸附和x-射线光电子能谱数据证实了氧化物包裹层的存在。发现亚纳米厚的氧化铝包裹层能够在600 C完全避免金纳米颗粒的团聚;相反,二氧化钛包裹层对金纳米颗粒稳定性的提高没有明显效果。通过CO氧化探针反应的活性测试,发现随着煅烧温度的升高氧化铝包裹的Au/TiO₂ 催化剂的活性逐渐提高,表明高温处理可以促进被包裹金原子的暴露并表现出催化活性。提供了提高金纳米颗粒稳定性的有效方法,为拓展金催化剂在条件苛刻的反应中的应用奠定了技术基础.     

Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows

We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al₂O₃, ZnO, TiO₂, and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al₂O₃, and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants.     

The influence of Fe,Cu, SiO<Subscript>2</Subscript>, TiO<Subscript>2</Subscript>, and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in aqueous solution on proton relaxation times

Measurements of proton nuclear spin-spin and spin-lattice relaxation times are applied for determining the concentration of solid-phase nanoparticles in nanofluids. This approach is tested for metal oxides SiO₂, TiO₂, Al₂O₃ and metal-carbon nanoparticles of 3d-metals Fe and Cu. It is shown that the sensitivity of the method for determining concentrations of 3d-metals is much higher than for oxides (by 2–4 orders of magnitude). It is revealed that measurement of the proton spin-spin relaxation time allows one to determine the concentration of Cu nanoparticles to 0.0001 mg/ml and that of Fe nanoparticles to 0.00001 mg/ml.     

Hall effect on MHD flow and heat transfer of nanofluids over a stretching wedge in the presence of velocity slip and Joule heating

This paper deals with the boundary layer flow and heat transfer of nanofluids over a stretching wedge with velocity-slip boundary conditions. In this analysis, Hall effect and Joule heating are taken into consideration. Four different types of water-base nanofluids containing copper (Cu), silver (Ag), alumina (Al₂O₃), and titania (TiO₂) nanoparticles are analyzed. The partial differential equations governing the flow and temperature fields are converted into a system of nonlinear ordinary differential equations using a similarity transformation. The resulting similarity equations are then solved by using the shooting technique along with the fourth order Runge-Kutta method. The effects of types of nanoparticles, the volume fraction of nanoparticles, the magnetic parameter, the Hall parameter, the wedge angle parameter, and the velocityslip parameter on the velocity and temperature fields are discussed and presented graphically, respectively.     

Preparation and electrochemical properties of nano Al<Subscript>0.2</Subscript>V<Subscript>2</Subscript>O<Subscript>5.3−<Emphasis Type="BoldItalic">δ</Emphasis></Subscript> cathode materials for rechargeable lithium batteries

Nano-sized Al³⁺-doped V₂O₅ cathode materials, Al_0.2V₂O_5.3−δ , were prepared by an oxalic acid assisted sol–gel method at 350 °C (sample A) and 400 °C (sample B). X-ray diffraction confirmed that samples A and B were pure phase Al_0.2V₂O_5.3−δ with an orthorhombic structure close to that of V₂O₅. Scanning electron microscopy showed that sample A was in nanoscale with a mean particle size about 50 nm. Cyclic voltammetry showed the good electrochemical and structural reversibility of the Al_0.2V₂O_5.3−δ nanoparticles during the Li⁺ insertion/extraction process. The Al_0.2V₂O_5.3−δ nanoparticles exhibited excellent charge–discharge cycling performance and rate capability compared to that of bulky V₂O₅ electrodes. For instance, the materials delivered a reversible specific capacity about 180 mAh g⁻¹ (sample A) and 150 mAh g⁻¹ (sample B), in the potential window of 4.0–2.0 V at the current density of 150 mA g⁻¹. The Al_0.2V₂O_5.3−δ nanoparticles in particular showed almost no capacity fading for at least 50 cycles.     

Experimental investigation and simulation of flow boiling of nanofluids in different flow directions

In this work, the flow boiling of TiO₂/water and Al₂O₃/water nanofluids was investigated experimentally and simulated with two phases. Experimental results were obtained in two directions and compared together. The volume fraction and heat transfer coefficient obtained from the vertical tube were compared with those obtained from the horizontal tube. The results showed that the contours of vapor volume fraction in horizontal tube are completely different from the vertical tube, which is due to the buoyancy effect. Moreover, the effect of nanoparticles on both flow directions was almost the same, while heat transfer coefficient was not the same in these flow directions. Based on the experimental result, presence of nanoparticles in the base fluid cannot increase the heat transfer coefficient.     

Band alignment and interfacial properties of atomic layer deposited (TiO2)x(Al2O3)1?x gate dielectrics on Ge

(TiO₂) _x (Al₂O₃)_1−x (x=0.7,0.8,0.9) gate dielectrics were deposited on Ge by atomic layer deposition using trimethylaluminium and Ti isopropoxide. The interfacial properties and band alignment were investigated by means of transmission electron microscopy (TEM) and X-ray photoemission spectroscopy. High-resolution TEM results show that the (TiO₂)_0.8(Al₂O₃)_0.2 film annealed at 500°C is amorphous with sharp interface between (TiO₂)_0.8(Al₂O₃)_0.2 and Ge. The conduction-band offsets are enhanced from 1.04 to 1.40 eV with increasing Al content. Capacitance equivalent thickness of 15.8 ? for (TiO₂)_0.9(Al₂O₃)_0.1 gate dielectrics is achieved with a gate leakage current of 2.70×10⁻⁵ A/cm² at V _g=+1 V.     

Minimum Polynomial for Single-Mode Parabose Parasupercharge and Hamiltonian

We calculate the minimum polynomial φ(x,y) of parasupercharge Q and Hamiltonian H for single-mode parabose parasupersymmetry (P-PSUSY). Suppose that φ(x,y) satisfies the homogeneity ∀ λ∈ℝ,φ(λ x,λ ² y)=λ ⁿ φ(x,y), then the parafermionic order p _f is restricted to either 1, 2, or 4. Under the P-PSUSY, the homogeneity of the φ(x,y) is equivalent to the parasuperconformality of Q and H. The physical meaning of the parasuperconformality is discussed, in connection with the spin of the elementary particle.     

TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles synthesized using He/Ar thermal plasma and their effectiveness on low-concentration mercury vapor removal

Oxygen-vacant titanium dioxide (TiO_2−x ) nanoparticles were synthesized using thermal plasma as a heating source at various applied plasma currents and He/Ar ratios. Samples with diverse characteristics were developed and the mercury removal effectiveness was subsequently evaluated. TiO₂ nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O₂ as precursors and Ar as plasma gas. TiO_2−x in anatase phase with a particle size at 5–10 nm was formed at the He/Ar volume ratio of 25/75. Further increasing the He/Ar ratio elevated the plasma temperature, causing the tungsten to melt, vaporize from the cathode, and then dope into the formed TiO₂ nanoparticles. The doped W appeared to inhibit the growth of nanoparticles and decrease the crystallinity of formed anatase. The effectiveness of oxygen-vacant sites on Hg⁰ removal under the visible light circumstance was confirmed. Hg⁰ removal by the TiO_2−x nanoparticles was enhanced by increasing the O₂ concentration. However, moisture reduced Hg⁰ capture, especially when light irradiation was applied. The reduction in Hg⁰ capture may be resulted from the competitive adsorption of H₂O on the active sites of TiO_2−x with Hg⁰ and transformed Hg²⁺.     

Numerical study of heat transfer enhancement of counter nanofluids flow in rectangular microchannel heat exchanger

This paper reports a numerical analysis of the performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids as the working fluids. Finite volume method was used to solve the three-dimensional steady, laminar developing flow and conjugate heat transfer in aluminum MCHE. The nanofluids used were Ag, Al₂O₃, CuO, SiO₂, and TiO₂ and the performance was compared with water. The thermal, flow fields and performance of the MCHE were analyzed using different nanofluids, different Reynolds numbers and different nanoparticle concentrations. Temperature profile, heat transfer coefficient, pressure profile, and wall shear stress were obtained from the simulations and the performance was discussed in terms of heat transfer rate, pumping power, effectiveness, and performance index. Results indicated enhanced performance with the usage of nanofluids, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The increase in nanoparticle concentration also yielded better performance at the expense of increased pressure drop.     

Biocorrosion studies of TiO<Subscript>2</Subscript> nanoparticle-coated Ti–6Al–4V implant in simulated biofluids

The corrosion behaviors of the TiO₂ nanoparticles coated bioimplant Ti–6Al–4V exposed to three different simulated biofluids (SBF), namely, (1) NaCl solution, (2) Hank’s solution, and (3) Cigada solution, were studied by using micro-Raman spectroscopy, electrochemical techniques, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The different electrochemical impedance spectroscopy models were applied to fit the data obtained from the implants before and after the coating of TiO₂ nanoparticles (50–100 nm). It was found that the TiO₂ nanoparticle coatings increased the thickness of the pre-existing oxide layer on the Ti–6Al–4V surface, serving to improve the bioimplant corrosion resistance.