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JitKang Lim David X. Tan Robert D. Tilton Sara A. Majetich 《Journal of magnetism and magnetic materials》2009,321(10):1557-1562
Peclet number analysis is performed to probe the convective motion of nanospheres and nanorods under the influence of magnetophoresis and diffusion. Under most circumstances, magnetophoretic behaviour dominates diffusion for nanorods, as the magnetic field lines tend to align the magnetic moment along the rod axis. The synthesis and dispersion of fluorophore-tagged nanorods are described. Fluorescence microscopy is employed to image the nanorod motion in a magnetic field gradient. The preliminary experimental data are consistent with the Peclet number analysis. 相似文献
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The design of a pressurized capillary rheometer operating at prescribed temperature is described to measure the viscosity of magnetic fluids (MFs) containing Fe3O4 magnetic nanoparticles (MNPs). The equipment constant of the rheometer was obtained using liquids with predetermined viscosities. Experimentally measured viscosities were used to evaluate different equations for suspension viscosities. Deviation of measured suspension viscosities from the Einstein equation was found to be basically due to the influence of spatial distribution and aggregation of Fe3O4 MNPs. By taking account of the coating layer on MNPs and the aggregation of MNPs in MFs, a modified Einstein equation was proposed to fit the experimental data. Moreover, the influence of external magnetic field on viscosity was also taken into account. Viscosities thus predicted are in good agreement with experimental data. Temperature effect on suspension viscosity was shown experimentally to be due to the shear-thinning behavior of the MFs. 相似文献
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M. M. Alimov 《Journal of Applied Mechanics and Technical Physics》2003,44(3):385-394
For low Peclet numbers, analytic expressions are obtained for three highest terms of the asymptotic expansion of the solution of the convective heat-transfer problem for a system consisting of two parallel plates with identical lengths identical and constant surface temperatures and an infinite uniform fluid flow with a low Prandtl number. 相似文献
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The channels formed between individual particles in porous media have variable dimensions and orientations. The porosity, permeability and its anisotropy exhibit random spatial distributions. The probabilistic approach can effectively describe the transport of contaminants through porous media and is analysed in this paper. Numerical results are obtained by considering (I) random dispersion coefficients without and with spatial structure, (II) random time distribution of concentration at the inlet boundary, (III) random velocity distribution in the flow field without and (IV) with variable dispersion coefficient, (V) non-linearity of the governing equation and (VI) anisotropy of the dispersion coefficient. Two methods are used for probabilistic predictions: (1) Gaussian field approach in conjunction with Monte Carlo method and (2) random walk method. The input random parameters are assumed to have normal and log-normal distributions according to available experimental data. The probability distribution functions of the contaminant concentration at different locations within the flow domain are calculated and compared with the input distributions as a function of the mean and fluctuation Peclet numbers. The one-dimensional case is analysed in detail and the illustrative numerical predictions are compared with analytical and experimental results. The extension to a two-dimensional domain is discussed in the last part of this paper. 相似文献
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Debapriya Chakraborty Nilanjana Bose Sukanya Sasmal Swagata Dasgupta Tapas K. Maiti Suman Chakraborty Sunando DasGupta 《Analytica chimica acta》2012
Aim of the present work is to investigate the reaction–diffusion process of a two species system under laminar flow in a T-shaped microchannel. A zone formed at the interface between the aqueous solutions of these two species is affected by advection and diffusion. Through theoretical analyses and experimental results, the effect of dispersion has been shown to influence this diffusion zone. We have defined a parameter called effective diffusivity, to account for the dispersion effects and observed it to be a function of the channel Peclet number. In the limiting case of low Peclet number, this parameter is constant and turns out to be equal to the molecular diffusivity. We have also related effective diffusivity and the dispersion coefficient through scaling estimates. 相似文献
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边界条件对对流扩散方程数值稳定性的影响 总被引:2,自引:0,他引:2
本文利用数值计算方法对采用均分网格的一维线性无源的对流-扩散方程在各种边界条件下的稳定性进行了分析,燕求出了不同边界条件下一维问题的中心差分和QUICK格式的临界网格Peclet数。指出按现有方法得出的临界网格Peclet数是判别差分格式对流数值稳定性的最苛刻的要求。对中心差分和QUICK格式,除两点边值问题以外的其它边界条件下的稳定性范围均不小于或远远大于两点边值问题的稳定性范围。通过计算还得出了格式的数值稳定性主要取决于计算区域下游侧的边界条件类型而与计算区域上游侧的边界条件类型无关的结论。 相似文献
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本从研究重力场中碰并面外无势力纳米气溶胶粒子之间的碰并出发.重力场中,纳米气溶胶粒子之间的碰并属于低peclet数高Knudsen数情况.求解纳米气溶胶间的对分布方程,得到了该条件下对分布函数的解析解.将结果和含有实力作用的匹配渐进展开法得到的三阶展式的情况做了比较,确定了该条件下Hamaker势力对对分布函数的贡献. 相似文献
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The design of a pressurized capillary rheometer operating at prescribed temperature is described to measure the viscosity of magnetic fluids (MFs) containing Fe3O4 magnetic nanoparticles (MNPs). The equipment constant of the rheometer was obtained using liquids with predetermined viscosities. Experimentally measured viscosities were used to evaluate different equations for suspension viscosities. Deviation of measured suspension viscosities from the Einstein equation was found to be basically due to the influence of spatial distribution and aggregation of Fe3O4 MNPs. By taking account of the coating layer on MNPs and the aggregation of MNPs in MFs, a modified Einstein equation was proposed to fit the experimental data. Moreover, the influence of external magnetic field on viscosity was also taken into account. Viscosities thus predicted are in good agreement with experimental data. Temperature effect on suspension viscosity was shown experimentally to be due to the shear-thinning behavior of the MFs. 相似文献
10.
In this paper we present a rigorous derivation of the effective model for enhanced diffusion through a narrow and long 2D
pore. The analysis uses the anisotropic singular perturbation technique. Starting point is a local pore scale model describing
the transport by convection and diffusion of a reactive solute. The solute particles undergo an adsorption process at the
lateral tube boundary, with high adsorption rate. The transport and reaction parameters are such that we have large, dominant
Peclet number with respect to the ratio of characteristic transversal and longitudinal lengths (the small parameter ). We give a formal derivation of the model using the anisotropic multiscale expansion with respect to . Error estimates for the approximation of the physical solution, by the upscaled one, are presented in the energy norm as
well as in L
∞ and L
1 norms with respect to the space variable. They give the approximation error as a power of and guarantee the validity of the upscaled model through the rigorous mathematical justification of the effective behavior
for small .
The research of A. Mikelić and C. Rosier was partially supported by the GDR MOMAS (Modélisation Mathématique et Simulations
numériques liées aux problèmes de gestion des déchets nucléaires) (PACEN/CNRS, ANDRA, BRGM, CEA, EDF, IRSN) as a part of the
project “Changements d’échelle dans la modélisation du transport multiphasique et réactif en milieux poreux : application aux milieux
fracturés et aux argiles”. 相似文献