An Investigation into Forced Convection of a Nanofluid Flowing in a Rectangular Microchannel under the Influence of a Magnetic Field

In line with recent studies,where it has been shown that nanofluids containing graphene have a stronger capacity to boost the heat transfer coefficient with respect to ordinary nanofluids,experiments have been conducted using water with cobalt ferrite/graphene nanoparticles.In particular,a circular channel made of copper subjected to a constant heatflux has been considered.As nanoparticles are sensitive to the presence of a magneticfield,different conditions have been examined,allowing both the strength and the frequency of such afield to span relatively wide ranges and assuming different concentrations of nanoparticles.According to thefindings,the addition of nanoparticles to thefluid causes its rotation speed to increase by a factor of two,whereas ultraviolet radiation plays a negligible role.The amount of time required to attain the maximum rotation speed of the nanofluid and the Nusselt number have been measured under both constant and alternating magneticfields for a ferrofluid with a concentration of 0.5%and atflow Reynolds number of 550 and 1750.

Magnetic Field Effect and Heat Transfer of Nanofluids within Waveform Microchannel

In this research,a numerical study of mixed convection of non-Newtonian fluid and magnetic field effect along a vertical wavy surface was investigated.A simple coordinate transformation to transform wavy surface to a flat surface is employed.A cubic spline collocation numerical method is employed to analyze transformed equations.The effect of various parameters such as Reynolds number,volume fraction 0-,Hartmann number,and amplitude of wave length was evaluated in improving the performance of a wavy microchannel.According to the presented results,the sinusoidal shape of the microchannel has a direct impact on heat transfer.By increasing the microchannel wave amplitude,the Nusselt number has risen.On the other hand,increasing the heat transfer in the higher wavelength ratio corrugated channel is seen as an effective method of increasing the heat transfer,especially at higher Reynolds numbers.The results showed that with increasing Hartmann numbers,the flow line near thewall becomesmore regular and,according to the temperature gradient created,theNusselt number growth.

Preparation and characterization of PEG-PEI/Fe_3O_4 nano-magnetic fluid by co-precipitation method

PEG-PEI/Fe3O4 nano-magnetic fluids with different mass fractions of reactant were prepared by co-precipitation method. Besides particle size analyzer,the methods of XRD,IR,VSM and AFM were adopted to characterize the synthesized samples. Covalent bonding of PEG,PEI and Fe3O4 exhibits superparamagnetism.The TEM photograph shows that the particles are of stable dispersion and little aggregation,with smooth surface,spherical shape and a diameter of about 80 nm,which meets the requirements of nano-materials.When the mass fraction of PEI in reactant is 25%,the particle size,Zeta-potential and pEGFP-C1 DNA loading efficiency are all satisfactory.In this case,PEG-PEI/Fe3O4 nano-magnetic fluids can be used as gene vectors or targeted drug carriers.

Characteristics of Nanofluids over a Non-Linearly Stretched Sheet under the Influence of Thermal Radiation and Magnetic Field

Recent studies carried out in terms of viscous flow and heat transfer of nano-fluids on the non-linear sheets. In this paper, detailed studies to understand the characteristics such as viscous flow and heat transfer of nano-fluids under the influence of thermal radiation and magnetic fields are studied using Keller-Box method. Various governing parameters affecting the viscous flow and heat transfers are drawn based on quantitative results. The raise in temperature affected the velocity to a negative value;however, the same observation was made even for the increasing magnetic field. The impact of radiation parameter is proportional seems to be proportional to temperature and it is observed to be inversely proportional with concentration.

Analysis of Casson Fluid Flow over a Vertical Porous Surface with Chemical Reaction in the Presence of Magnetic Field

Casson fluid flow over a vertical porous surface with chemical reaction in the presence of magnetic field has been studied. A similarity analysis was used to transform the system of partial differential equations describing the problem into ordinary differential equations. The reduced system was solved using the Newton Raphson shooting method alongside the Forth-order Runge-Kutta algorithm. The results are presented graphically and in tabular form for various controlling parameters.

Process Modeling of Ferrofluids Flow for Magnetic Targeting Drug Delivery

Among the proposed techniques for delivering drugs to specific sites within the human body, magnetic targeting drug delivery surpasses due to its non-invasive character and its high targeting efficiency. Although there have been some analyses theoretically for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel of human body. This paper presents a mathematical model to describe the hydrodynamics of ferrofluids as drug carriers flowing in a blood vessel under the applied magnetic field. A 3D flow field of magnetic particles in a blood vessel model is numerically simulated in order to further understand clinical application of magnetic targeting drug delivery. Simulation results show that magnetic nanoparticles can be enriched in a target region depending on the applied magnetic field intensity. Magnetic resonance imaging confirms the enrichment of ferrofluids in a desired body tissue of Sprague-Dawley rats. The simulation results coincide with those animal experiments. Results of the analysis provide the important information and can suggest strategies for improving delivery in favor of the clinical application.

Anomalous reactivity of thermo-bioconvective nanofluid towards oxytactic microorganisms

The peristaltic flow of a non-Newtonian nanofluid with swimming oxytactic microorganisms through a space between two infinite coaxial conduits is investigated. A variable magnetic field is applied on the flow. The bioconvection flow and heat transfer in the porous annulus are formulated, and appropriate transformations are used, leading to the non-dimensionalized ruling partial differential equation model. The model is then solved by using the homotopy perturbation scheme. The effects of the germane parameters on the velocity profile, temperature distribution, concentration distribution, motile microorganism profile, oxytactic profile, pressure rise, and outer and inner tube friction forces for the blood clot and endoscopic effects are analyzed and presented graphically.It is noticed that the pressure rise and friction forces attain smaller values for the endoscopic model than for the blood clot model. The present analysis is believed to aid applications constituting hemodynamic structures playing indispensable roles inside the human body since some blood clotting disorders, e.g., haemophilia, occur when some blood constituents on the artery wall get confined away from the wall joining the circulation system.

Lubrication Property of Magnetorheological Fluid With Nano-Silica Additives Under Magnetic Field

Magnetorheological(MR)fluid is colloidal suspension and stiffens into semi-solid when subjected to a magnetic field.In order to investigate the effect of magnetic field on lubrication property of MR fluid with nano-silica additives,a pin-on-disc tribometer is used to carry out friction and wear experiment of steel under the magnetic field.The MR fluids with different additive concentrations are prepared and their theological properties are examined via a rotational rheometer.Different lubrication performance of the MR fluid with nano-silica additives with and without magnetic field is presented.In addition,through observing the morphology and analyzing the elemental composition of the worn surfaces,the effects of additives on the lubrication property are investigated.

纳米磁流体在驱油应用中的研究进展

综述了基于磁性纳米材料所构建的纳米磁流体在提高原油采收率中的应用;总结了纳米磁流体的驱油机理,重点论述了基于氧化铁、钴铁氧体和镍铁氧体等磁性纳米材料所构建的纳米磁流体在提高原油采收率中的应用进展;最后对纳米磁流体在驱油应用中所面临的挑战和机遇进行了总结和展望。

磁场对纳米铁酸镍(NiFe_(2)O_(4))磁流体金属腐蚀行为研究

为探究磁场条件下金属在纳米磁流体中的腐蚀问题,通过两步法制备了纳米NiFe_(2)O_(4)磁流体,采用重量法探究了磁场条件下铜片在纳米磁流体介质中的腐蚀速率,并分析了不同分散剂及其质量分数、pH值、纳米NiFe_(2)O_(4)颗粒质量分数和磁场强度对铜片腐蚀速率的影响。实验结果表明,油酸以及十二烷基硫酸钠都抑制了铜片的腐蚀。并且十二烷基硫酸钠的抑制效果更好;碱性条件下铜片腐蚀速率低于酸性条件下;纳米磁性颗粒的加入一定程度上促进铜片的腐蚀;磁场强度可以提高铜片在纳米磁流体介质中的耐腐蚀性,随着磁场强度的增加,铜片的腐蚀速率逐渐减小。

Analysis of the factors affecting the magnetic characteristics of nano-Fe_3O_4 particles

We prepared Fe3O4 nanoparticles using chemical coprecipitation and studied the factors affecting the magnetic characteristics of nano-Fe3O4 particles.We identified four factors and three levels of an orthogonal experiment and investigated these four factors that affect the magnetic characteristics of the Fe3O4 particles.We obtained important information from this investigation.The Fe3+ to Fe2+ molar ratio,the iron precursor salt,the amount of surfactant and the amount of alkali were found to be important.We also studied the influence of the order of alkali and surfactant addition,the aging time and the stirring speed on the magnetic characteristics of the nano-Fe3O4 particles.The Fe3O4 preparation process was also analyzed.

PAO3基磁性流体的摩擦学性能研究

制备了以Fe_(3)O_(4)为磁性纳米粒子的航空基础油(PAO3)基磁性液体,通过X射线透射仪(XRD)、场透射电镜(TEM)、震动磁强计(VSM)和静置试验对其进行表征,并将其作为润滑油进行研究.与基础油PAO3进行对比,共同考察了在不同摩擦对偶上的摩擦学性能.通过扫描电子显微镜(SEM)、能谱仪(EDS)、轮廓仪和光学显微镜,测试了其在12CrNi4A钢/304钢、12CrNi4A钢/GCr15钢和12CrNi4A钢/Si3N4陶瓷摩擦副上的摩擦学性能,探究了其润滑机理.结果表明:所制备的磁性液体能够稳定分散,满足磁性液体标准.相比于基础油,磁性液体的摩擦学性能受到多因素的影响,在一定条件下具有优异的减摩和抗磨性能.这主要归因于纳米Fe_(3)O_(4)粒子对摩擦副表面氧化膜的去除与修复以及浓度和磁场对其分散性与团聚性的影响.

纳米磁性流体与表面织构对钛合金的协同减摩作用机制

目的 提高钛合金表面的摩擦学性能。方法 采用纳秒激光器在钛合金表面构造沟槽型微织构图案,并以水基纳米磁流体和去离子水为润滑剂,利用UMT-3摩擦磨损试验机探究了织构与纳米磁流体的协同减摩作用机制。结果 分析了不同润滑条件下,沟槽型织构的分布间距对钛合金表面摩擦磨损性能的影响,在织构与纳米磁流体的协同作用下,钛合金表面的摩擦学性能得到改善,织构间距为250μm时的摩擦学性能最好,摩擦因数最大降低约51.5%,磨损率最大降低77.6%。当织构间距过小,织构化表面承载区减少,导致织构磨损较快,而织构间距过大会弱化织构效果。其次,以最优织构间距为基础,进一步探究了不同表面织构形貌和深度对钛合金表面摩擦学性能的影响。最后,研究了最优织构参数下,滑动速度和加载载荷对钛合金减摩性能的影响。结论 在润滑条件下,织构的表面形貌和深度影响钛合金表面的摩擦学性能,织构深度太浅或太深时,其流体动压效应都会减弱,从而导致摩擦因数和磨损量增大;当产生足够大的动压效应时,织构边缘的凸起结构能够对织构起到保护作用,延缓织构磨损。

机械工程领域中的纳米技术及其应用

纳米材料在机械工程领域被广泛使用,它的应用将改变传统的机械操作模式,对机械工程具有重要的影响。为进一步推动纳米技术在机械工程领域的发展与应用,首先阐述了纳米技术的概念,然后从微型纳米轴承、纳米技术马达、纳米燃油装置、纳米刀具以及纳米磁性液体在旋转轴中的应用等方面,对纳米技术在机械工程中的应用进行了探讨,最后分析了纳米技术在机械工程领域中的发展前景。

油酸包覆Fe_3O_4纳米粒子的红外光谱研究

液相共沉积法制备正庚烷基磁性液体,为了研究油酸对纳米粒子的包覆作用,采用红外光谱分别测试Fe3O4纳米粒子、油酸及正庚烷基铁氧体磁性液体。比较其结果得出,油酸通过端羧基与Fe3O4纳米粒子之间的化学反应来实现对其表面包覆,包覆过程没有破坏油酸的非极性链,确保包覆后的油酸具有与非极性载液相容性,此为磁性液体表面活性剂的本质作用。

金属磁性液体的制备

探讨了 Ｆｅ（ＣＯ）５热分解条件和表面活性剂对制备金属磁性液体的影响。结果表明，在Ｆｅ（ＣＯ）５热分解温度为１８０～２２５℃、Ｆｅ（ＣＯ）５蒸发温度为 ３０～５０℃、稀释比为 ３０： １～５０：１的条件下，采用亚胺或复合型表面活性可以制备性能较好的金属磁性液体。

诸因素对制备氮化铁磁性液体的影响

探讨了Fe（CO）5热分解温度（Fe的氮化温度）、NHa流量及表面活性剂对制备氢化铁磁性液体的影响结果表明，将Fe（CO）5热分解温度控制在180—210℃，并通入过量的NH3及采用与纳米级氮化铁磁性颗粒和载液相匹配的表面活性剂可以制备出性能较好的氮化铁磁性液体.

纳米Fe_3O_4/聚苯乙烯均匀分散体系的制备及结构

用化学共沉淀法制备了Fe_3O_4纳米颗粒,以油酸为表面活性剂,苯乙烯为载液,制备了稳定的纳米Fe_3O_4可聚合磁流体,将可聚合磁流体经自由基引发聚合制成纳米Fe_3O_4/聚苯乙烯均匀分散体系,用WAXRD研究了Fe_3O_4纳米粒子的结晶情况;用FTIR研究了油酸表面改性前后Fe_3O_4粒子表面官能团的变化;用TEM研究了Fe_3O_4颗粒的粒径大小及其在苯乙烯单体和聚苯乙烯中的分散情况;用DSC和TGA研究了纳米Fe_3O_4/聚苯乙烯均匀分散体系的玻璃化转变温度(T_g)和热稳定性,结果表明,合成的纳米Fe_3O_4为立方晶型,平均粒径在10nm左右,油酸分子在Fe_3O_4表面是化学吸附,经表面处理的Fe_3O_4超细颗粒在苯乙烯和聚苯乙烯基体中分散较均匀。界面粘结较好,含1.8％Fe_3O_4纳米颗粒的聚苯乙烯的最大热失重温度比聚苯乙烯提高了13 K,Fe_3O_4/聚苯乙烯复合体系的饱和磁化强度σ_s为17.43 emu/g。

磁性液体的研究进展

本文综述了国内外磁性液体的研究现状与进展 ,系统地介绍了磁性液体的理论、现有种类、制备方法 ,并在此基础上对磁性液体的性能特点和应用进行了论述 。