Radiative transfer in a two-dimensional rectangular annulus medium

The radiative transfer equation in a two-dimensional rectangular annulus medium is solved numerically. The numerical method is based on a finite difference scheme and a product quadrature discrete-ordinate scheme. The discretized equation of transfer is solved iteratively to give the radiation intensity. The medium is assumed to absorb, emit, and anisotropically scatter radiation. It is exposed to diffusely emitting and diffusely reflecting boundaries. The results of the total intensity for various radiative parameters are presented. The method can be modified easily to solve the rectangular medium without the annulus. Our results in this case compare very well with those of Crosbie et al. [1], Thynell et al. [2], and Wu [3].     

A Unified Study on the Cyclicity of Period Annulus of the Reversible Quadratic Hamiltonian Systems

The cyclicity of the period annulus of reversible quadratic Hamiltonian systems under quadratic perturbations was studied by several authors for different cases by using different methods. In this paper, we study this problem in a unified way.     

PERTURBATION SOLUTION OF NON-NEWTONIAN FLUID AXIAL LAMINAR FLOW THROUGH ECCENTRIC ANNULI

Using the perturbation method, the axial laminar flow of Non-Newtonian fluid through an eccentric annulus is studied in the present paper. The relative eccentricity ε is taken as a perturbation parameter, and the first order perturbation solutions of the problem, such as velocity field, limit velocity and pressure gradient, are all obtained.     

最大偏心圆环空间自然对流传热的数值分析

采用正切圆坐标变换 ,对不同直径比以及上、下、侧面三种偏心位置 ,偏心率达到最大值± 1的变壁温水平圆柱环形封闭空间内空气的自然对流传热进行了数学模拟 ,求出的二维空间温度分布与实验拍摄相应的温度干涉条纹图片吻合良好。计算结果同时给出流线分布及内、外壁面的局部传热系数、热流量。并与现有的偏心率小于 1的有关资料作对比分析。数值计算的范围是 :2 .0× 1 0 2 ≤ Ra≤ 3 .0× 1 0 5,1 .3≤ Do/Di≤ 3 .8,Pr=0 .70 6,|ε|=1 .     

Numerical investigation of fully developed laminar flow in irregular annuli: Square‐circular ducts

Numerical study is carried out on fully developed laminar axial flow of incompressible Newtonian fluid in irregular annuli of different cross‐sectional geometry. Accurate prediction of the friction factor of this flow was obtained using high‐order finite element method. Investigations are performed for the annular flow between rectangular and circular ducts under all possible arrangements. The governing equations are solved by an efficient finite element technique. It was found that a higher annular area‐ratio will lead to a monotonic increase in (f Re) value in the case of regular annuli, and will lead to an increase followed by a decrease in (f Re) value in the case of irregular annuli. Furthermore, this study illustrates that irregular annuli have lower (f Re) value than regular annuli, and that the square‐in‐circle case (SC‐case) has the lowest (f Re) value whereas the circle‐in‐circle case (CC‐case) has the highest (f Re) value. The finite element technique developed in this study was validated against the already reported numerical results in the literature, and the results presented in this work show excellent agreement. Copyright © 2009 John Wiley & Sons, Ltd.     

偏心环形腔内冷水稳态自然对流的数值模拟

为了了解偏心环形腔内非Boussinesq流体自然对流换热的特有现象和规律,本文利用有限容积法对垂直偏心环形腔内的冷水自然对流进行了二维数值模拟,得到了半径比为1.5时不同密度倒置参数、偏心率和Rayleigh数下的流场和温度场,并对不同条件下的平均Nusselt数进行了比较和分析。结果表明:密度倒置参数对流型结构起着决定性的作用,偏心率和Rayleigh数对流场影响较小;相同条件下,当密度倒置参数在0.5附近时,平均Nusselt数最小。     

疏水表面减阻环带实验研究

针对疏水功能材料在流动减阻方面的应用, 选取典型不同粗糙度、不同疏水性的功能涂层表面, 通过新型环带实验研究了其阻力特性, 并获得了相应的扭矩和减阻率曲线. 实验采用测量圆盘带动环带旋转时的扭矩的方法间接计算环带表面所受的摩阻, 突破了传统微管道实验在尺度上的限制, 避免了水洞实验中影响因素过多的弊端, 对疏水材料的宏观应用有着重要意义. 实验证实了在宏观尺度下疏水涂层在低雷诺数时的减阻作用; 但在高雷诺数时, 减阻作用减弱, 甚至部分涂层有增阻作用, 而压差阻力的迅速增大是造成增阻的主要原因. 通过对比分析认为: 低雷诺数时, 疏水特性对于减阻效果影响更大; 而高雷诺数时, 粗糙度起更大作用, 甚至可能起到增阻的反效果. 关键词： 疏水表面 环带实验 粗糙度 减阻     

Images of an incoherent annulus in the presence of transverse sinusoidal vibrations

The diffraction image of an incoherent bright annular test object is obtained by using Fourier transform method. The effect of transverse sinusoidal vibrations has been studied and results are given in graphical form for various sizes of the object. It is observed that in certain cases the presence of vibrations completely distorts the object. Hence a detailed analysis of image intensity distribution should prove useful in aerial reconnaissance work and performance evaluation tests.     

Dehn surgery on knots in solid tori creating essential annuli

Let be a -manifold obtained by performing a Dehn surgery on a knot in a solid torus. In the present paper we study when contains a separating essential annulus. It is shown that does not contain such an annulus in the majority of cases. As a corollary, we prove that symmetric knots in the -sphere which are not periodic knots of period satisfy the cabling conjecture. This is an improvement of a result of Luft and Zhang. We have one more application to a problem on Dehn surgeries on knots producing a Seifert fibred manifold over the -sphere with exactly three exceptional fibres.

     

Energy and Entropy Production of Nanofluid within an Annulus Partly Saturated by a Porous Region

The flow and heat transfer fields from a nanofluid within a horizontal annulus partly saturated with a porous region are examined by the Galerkin weighted residual finite element technique scheme. The inner and the outer circular boundaries have hot and cold temperatures, respectively. Impacts of the wide ranges of the Darcy number, porosity, dimensionless length of the porous layer, and nanoparticle volume fractions on the streamlines, isotherms, and isentropic distributions are investigated. The primary outcomes revealed that the stream function value is powered by increasing the Darcy parameter and porosity and reduced by growing the porous region’s area. The Bejan number and the average temperature are reduced by the increase in Da, porosity ε, and nanoparticles volume fractions ϕ. The heat transfer through the nanofluid-porous layer was determined to be the best toward high rates of Darcy number, porosity, and volume fraction of nanofluid. Further, the local velocity and local temperature in the interface surface between nanofluid-porous layers obtain high values at the smallest area from the porous region (D=0.4), and in contrast, the local heat transfer takes the lower value.