脉动流化床内球柱形颗粒流动行为研究

本文结合离散单元模型和计算流体力学方法对脉动流化床内气固流动特性进行数值模拟.结果表明,脉动气流的波形和振幅对球柱形颗粒的流动行为有明显的影响.方波脉动气流作用下的时均颗粒总平动和旋转动能最大,其次是正弦波脉动和三角波脉动,恒定气流下的最小.功率谱分析结果可以发现方波气流下主频幅度最大,其次是正弦波、三角波和恒定气流....     

The Flow Patterns and Wall Stresses in a Louvered‐Wall Moving Granular Filter Bed of Quartz Sand

The flow patterns and wall stresses in a two‐dimensional louvered moving granular filter bed of quartz sand were investigated. The flow pattern histories of granular solids in the filter bed were recorded using a digital camcorder and a pressure gauge for simultaneously measuring the normal stresses as well as shear stresses of the granular solids. The static wall stress distributions produced by the granular solids were measured, and agreed with a theoretical prediction formed using the differential slice and Runge‐Kutta (order four) methods. The variations in the dynamic wall stresses with time in a moving granular filter bed were obtained and the effect of the louver angle upon the flow patterns and wall stresses was also investigated. Employing the results obtained by stress measurements and image processing, the wall pressure pulsation phenomena in a moving granular filter bed may be further understood. The results reported here provide fundamental information for the design of moving granular filter beds to act as high‐temperature flue gas cleanup filters.     

Structural and Thermodynamic Peculiarities of Core-Shell Particles at Fluid Interfaces from Triangular Lattice Models

A triangular lattice model for pattern formation by core-shell particles at fluid interfaces is introduced and studied for the particle to core diameter ratio equal to 3. Repulsion for overlapping shells and attraction at larger distances due to capillary forces are assumed. Ground states and thermodynamic properties are determined analytically and by Monte Carlo simulations for soft outer- and stiffer inner shells, with different decay rates of the interparticle repulsion. We find that thermodynamic properties are qualitatively the same for slow and for fast decay of the repulsive potential, but the ordered phases are stable for temperature ranges, depending strongly on the shape of the repulsive potential. More importantly, there are two types of patterns formed for fixed chemical potential—one for a slow and another one for a fast decay of the repulsion at small distances. In the first case, two different patterns—for example clusters or stripes—occur with the same probability for some range of the chemical potential. For a fixed concentration, an interface is formed between two ordered phases with the closest concentration, and the surface tension takes the same value for all stable interfaces. In the case of degeneracy, a stable interface cannot be formed for one out of four combinations of the coexisting phases, because of a larger surface tension. Our results show that by tuning the architecture of a thick polymeric shell, many different patterns can be obtained for a sufficiently low temperature.     

正冲击波后固壁表面颗粒的上升运动

为揭示固壁表面颗粒的冲击波夹卷本质,模拟垂直于固壁表面的正冲击波后单个颗粒的上升运动.假定颗粒初始时刻处于气载状态(因波的反射或碰撞离开壁面),受Saffman升力、气动阻力和重力作用.模型方程为波后定常气流边界层方程和颗粒运动常微分方程,分别用单参数法和四阶龙格库塔法求解.计算颗粒速度与轨迹表明:颗粒的冲击波卷扬动力...     

周期性波纹通道内换热与流动的数值研究

采用曲线坐标系下压力与速度耦合的SIMPLER算法,数值研究了一种紧凑换热器中波纹通道内周期性充分发展的层流流动与换热情况,流动Re数的范围为100~1100,Pr数为0.7.计算考察了不同波纹高度、波纹间距对流动与换热的影响,并对模型参数进行了性能评价.计算结果表明,整体Nu数及fRe数随着流动Re数的增加而增加.随着波纹高度的增加或波纹间距的减小,换热增强,特别是在高Re数下波纹高度的增加更加强化换热.最佳波纹高度和间距分别为1.15 mm和13 mm.     

Flow of Newtonian Fluid in Non-Uniform Tubes with Application to Renal Flow: A Numerical Study

In this paper, a numerical method employing a finite difference technique is used for an investigation of viscous, incompressible fluid flow in a tube with absorbing wall and slowly varying cross-section. The effect of fluid absorption through permeable wall is accounted by prescribing flux as a function of axial distance. The method is not restricted by the parameters in the problem such as wave number, permeability parameter, amplitude ratio and Reynolds number. The effects of these parameters on the radial velocity and mean pressure drop are studied and the results are presented graphically. Comparison is also made between the results obtained by perturbation method of solution and present approach.     

全尺度方法对颗粒与流体之间相交换量研究

本文采用了内嵌边界多重直接力算法全尺度计算研究了三维空间中颗粒群在重力作用下沉降时,颗粒群与流体之间的相互作用过程。结合多相流的欧拉-欧拉双流体模型方法中对颗粒群与流体之间相互作用力的处理方式,分析了颗粒与流体之间的相交换量。并把全尺度计算得到的颗粒群与流体之间的相交换量与本文中提到的单颗粒受力模型(SPM)和颗粒群受力模型(GPM)对相互作用力进行了比较分析。     

On the Theory of Electric-Current Flow through a Mixture of Charged Particles

Current conduction through a mixture made of two species of positively charged particles is considered where one of the latter species participates in the exchange with the surrounding medium. A solution to the electrodiffusion equations together with Poisson's equation is obtained in the first approximation in terms of the small parameter. A condition is determined where the distribution of charged particles involved in the exchange with the surrounding medium is derived using the diffusion equation for neutral particles. It is shown that the solution to the electrodiffusion equations contains a component decaying with time.     

Fluid adsorption at the base of a cylinder

We consider the adsorption of fluid at a cylinder protruding from a flat substrate. For small contact angles θ, a liquid drop condenses at the base, the size of which is determined by macroscopic arguments. The adsorption exhibits scaling behavior related to a number of phase transitions and, for systems with short-ranged forces, shows a remarkable property: for small θ, the height and width of the drop are near identical to expressions for the thickness and parallel correlation length for microscopic wetting films. The only difference is that the bulk correlation length is replaced by the cylinder radius. This geometrical amplification of the microscopic lengths occurs for second-order, first-order, and complete wetting transitions, and is specific to three dimensions. Similar phenomena occurs for long-ranged forces, and shows crossover scaling behavior.     

Influence of a Kerr-Like Medium and the Detuning Parameter on the Statistical Aspects of the Intensity-Dependent-Coupling Hamiltonian

We study the interaction between a one-mode electromagnetic field and a two-level atom in the presence of a Kerr-like medium when the atom is prepared initially in the momentum eigenstate. The wave function is calculated by using the Schrodinger equation for a coherent electromagnetic field and an atom in the excited state. The effects of the Kerr-like medium and the detuning parameters on the statistical aspects of the intensity-dependent-coupling Hamiltonian such as, atomic momentum increment, momentum diffusion, the radiation force, and the field entropy are calculated. We investigate the effect of the detuning, Kerr-like medium and photon number operator on the field entropy.     

堆积床内非驻定过滤燃烧的一维研究

多孔介质内气体过滤燃烧不同于自由流中燃烧,燃气与多孔介质强烈换热.热波波速和燃烧波波速是燃烧过程的特征参数.以惰性堆积床内的甲烷/空气的低速过滤燃烧为例,提出一维解析模型,用摄动理论推导出燃烧波波速,用直接求解方法和格林函数方法给出充分发展后的和瞬态的燃烧温度分布,并进行计算验证.     

A Fractal Model for the Effective Thermal Conductivity of Granular Flow with Non—uniform Particles

The equipartition of energy applied in binary mixture of granular flow is extended to granular flow with non-uniform particles.Based on the fractal characteristic of granular flow with non-uniform particles as well as energy equipartition,a fractal velocity distribution function and a fractal model of effective thermal conductivity are derived.Thermal conduction resulted from motions of particles in the granular flow,as well as the effect of fractal dimension on effective thermal conductivity,is discussed.     

Advanced Study of Unsteady Heat and Chemical Reaction with Ramped Wall and Slip Effect on a Viscous Fluid

This paper investigate the effect of slip boundary condition, thermal radiation, heat source, Dufour number,chemical reaction and viscous dissipation on heat and mass transfer of unsteady free convective MHD flow of a viscous fluid past through a vertical plate embedded in a porous media. Numerical results are obtained for solving the nonlinear governing momentum, energy and concentration equations with slip boundary condition, ramped wall temperature and ramped wall concentration on the surface of the vertical plate. The influence of emerging parameters on velocity,temperature and concentration fields are shown graphically.     

An Ideal-Fluid Flow through a Stationary Granular Layer in the Presence of a Flat Wall

Doklady Physics - The problem of the flow of an ideal incompressible fluid is considered along a flat surface, perpendicular to which a stationary granular layer is located. The granular-layer...     

The Transmission of a Sampling Orifice for Charged and Excited Particles in the Molecular Flow Range

The transmission of a circular orifice in the molecular flow range is calculated for the case that the particular state of particles flowing through the orifice is affected by wall collisions. The deactivation of metastable atoms and the neutralisation of charged particles at the orifice tube wall is taken into account. The results give a detailed illustration of the fate of particles passing an extraction orifice, namely the fraction of particles passing without wall collision, the fraction passing after one and after multiple wall reflections as a function of the characteristic dimensions of the orifice and the reflection coefficient.