微通道内电渗压力混合驱动幂律流体流动模拟

为了研究微通道内电渗压力混合驱动幂律流体的流动特性,建立了微通道内电渗压力混合驱动幂律流体的计算模型,其双电层电势、流体的流场分布分别由Poisson-Boltzmann(P-B)方程和Navier-Stokes(N-S)方程描述.讨论了无量纲Debye(德拜)参数K、壁面ζ*电势和幂律指数n对流体流动特性和Poiseuille数的影响.结果表明,当压力梯度与外加电场方向一致(Γ0)时,剪切变稀流体的速度大于剪切变稠流体;压力梯度与外加电场方向相反(Γ0)时,结果相反.Poiseuille数是无量纲Debye常数K、壁面ζ*电势和幂律指数n的增函数.     

Numerical Method for Solving a Premixed Laminar Flame

A splitting-up method, which splits the chemical kinetic terms from the flow terms, is presented to solve time-dependent, one-dimensional, laminar, premixed flame problems. An example for studying the development of an ozone decomposition flame is calculated. A movable boundary technique is adopted, so that the number of grid points can be significantly reduced. Special care is taken to maintain the accuracy of the solution. The results are checked in many ways. All checks show that the present method is satisfactory.     

矩形微通道热沉内单相稳态层流流体的流动与传热分析

采用解析方法分析了矩形微通道热沉内单相稳态层流流体的流动与传热．基于y方向流速和导热不变的假设,建立流体在矩形微通道内流动的流速方程和传热的温度方程,进而推导出Nusselt数和Poiseuille数的理论表达式．通过计算结果可以看出,推导的Nusselt数和Poiseuille数的解析解与其他文献的结果吻合较好,而且当宽高比趋于无穷大时,Nusselt数和Poiseuille数分别趋近于8.235和96,这与其他文献结果完全相同．在Reynolds数相同时,摩擦因数随着宽高比的增加而增加,而在相同宽高比时,摩擦因数随Reynolds数的增加而减小．     

两种互不相溶流体在竖直的波状壁面和平行的平面壁面间作不稳定的混合对流传热

分析粘性、不可压缩、互不相溶流体,在竖直的波状壁面和光滑的平面壁间,传热传质混合对流的组合效应.得到无量纲控制方程的摄动解:0阶的均值部分和1阶的摄动部分.将所得到的1阶量,用小波长摄动级数展开,出现按指数阶分类的方程组.得到了0阶和1阶的解析表达式及其整体解,通过数值计算,用图形表明流体流动的显著特征以及传热特性.界面上应用适当的匹配条件,使分离的解相匹配.还针对控制参数的不同变化,分析了剪应力和Nusselt数的变化.发现Grashof数、粘性比、宽度比和导电率,对平行于流动方向的速度是有利的,对垂直于流动方向速度的影响正相反.     

粘性流体间夹有多孔介质时的非定常流动及其热传导

粘性流体间夹有多孔介质,流经壁面温度等温的水平管道时,研究其非定常振荡流动及其热传导问题.多孔介质中的流动采用Brinkman方程模型.通过集中非周期项和周期项,将偏微分的控制方程转化为常微分方程,并利用边界和界面条件,找到了每个区间的闭式解.数值计算了各种物理参数,如多孔性参数、频率参数、周期频率参数、粘度比、热传导系数比和Prandtl数,对速度和温度场的影响,并给出相应的图形.此外,导出了壁顶和壁底处的热传递率并用表格列出.     

Numerical Analysis of Heat Transfer for Cooling of Photovoltaic Cells

Photovoltaic cells are devices which convert solar radiation directly into electricity. However, solar radiation increases the photovoltaic cells temperature [1] [2]. The temperature has an influence on the degradation of the cell efficiency and the lifetime of a PV cell. This work reports on a cooling water technique for cells, whereby the cooling system was placed at the front surface of the cells to dissipate away excess heat and to block unwanted radiation. Using water as a cooling medium for the cells, the overheating of closed panel is greatly reduced without prejudicing luminosity and water acts as a filter to remove a portion of solar spectrum in the infrared band but allows transmission of the visible spectrum most useful for the PV operation. The aims of this study are to develop a 3D thermal model to simulate the cooling and heat transfer in Photovoltaic panel and recommend a cooling technique for the PV panel. In order to have a good estimation for the temperature distribution, the three-dimensional flow and heat transfer across the cooling block is investigated numerically by solving the continuity, momentum and energy equations using FLUENT. The second objective of this work is to study the influence of the geometrical dimensions of the panel, water mass flow rate and water inlet temperature on the flow distribution and the solar panel temperature. The results obtained by the model are compared with experimental results from testing the prototype of the cooling device. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

T型微通道内液滴在幂律流体中运动机理的格子Boltzmann方法研究北大核心CSCD

采用非Newton不可压两相流格子Boltzmann模型研究了T型微通道内Newton液滴在非Newton幂律流体中的运动过程.研究了非Newton流体幂律指数n、主管道毛细数Ca、两相流量比Q、两相黏度比M以及主管道壁面润湿性θ对液滴在T型微通道内的形成尺寸、形成时间和变形参数(DI)的影响.研究结果表明:首先,主管道流体幂律指数n从0.4增加到1.6时,液滴的形成尺寸近似呈线性减小,而液滴的形成时间和变形参数先快速减小,然后缓慢减小;其次,黏度比对液滴形成尺寸、液滴形成以及变形参数的影响与幂律指数的影响基本一致;再者,随着Ca和主管道壁面润湿性的增加,形成液滴的尺寸近似呈线性减小,形成液滴的时间和变形参数先快速减小然后缓慢减小,且减小趋势随幂律指数的增加而减缓;最后,研究结果还表明主管道和子管道的流量比Q越大,液滴形成时间越长,液滴形成尺寸和变形参数越小.     

A Numerical Method for Solving Matrix Coefficient Heat Equations with Interfaces

In this paper, we propose a numerical method for solving the heat equations with interfaces. This method uses the non-traditional finite element method together with finite difference method to get solutions with second-order accuracy. It is capable of dealing with matrix coefficient involving time, and the interfaces under consideration are sharp-edged interfaces instead of smooth interfaces. Modified Euler Method is employed to ensure the accuracy in time. More than 1.5th order accuracy is observed for solution with singularity (second derivative blows up) on the sharp-edged interface corner. Extensive numerical experiments illustrate the feasibility of the method.     

精确计算Bingham流体圆管层流压降及速度分布规律的新方法

Bingham(宾汉)模型情况下,多采用通用公式进行圆管层流压降的解析计算,即将Bingham模型本构方程代入粘性流体圆管层流流动通用公式进行计算,仅能得到压降的解析解.新方法结合Bingham流体本构方程与运动方程,建立有关力学平衡方程,并运用代数方程的根式解理论对圆管层流流动时的非线性方程进行求解,可直接求得Bingham流体圆管层流压降及速度流核区半径的解析解,进一步可求得圆管层流速度解析解;Bingham流体圆管层流速度的直接影响因素为流量、塑性粘度和屈服值,研究发现速度流核宽度与屈服值成正比,与流量及塑性粘度成反比,且流核的宽度越大,流核区的速度越小.     

纳米流体强化传热问题的高效算法设计及其高精度数值模拟

对周期性温度边界条件下方腔内Copper-水纳米流体的对流传热问题建立了完全四阶高精度紧致差分格式,并探讨了该格式高效算法设计,同时引入伪时间导数项采用Von Neumann方法证明了格式的绝对稳定性.研究了不同Ri数下纳米颗粒体积分数、左右边界温度的正弦振幅比和相位偏差对纳米流体传热效率的影响.数值结果表明,对于给定的Ri数,随着纳米颗粒体积分数的增大和边界温度的正弦振幅比的增加,纳米流体的传热效果会显著增强,而相位偏差只影响方腔右侧的温度分布.     

层射流的格子Boltzmann方法的数值模拟

通过引入一种格子Boltzmann方法的特殊边界处理,对对称和非对称的层射流进行有效的数值研究,模拟结果与已有的数值结果非常吻合.表明了格子Boltnnann方法解层射流问题的高效与稳定.     

On Analytical Results for the Optimal Control of the quasi-stationary Radiative Heat Transfer System

We state an optimal control problem of the coupled quasi-stationary radiative heat equations consisting of the radiative transfer equation and the instationary heat transfer equation that model radiative-conductive heat transfer. We give an existence and uniqueness result for the state equations and the adjoint equations of the quasi-stationary radiative heat transfer system. For the optimal control problem the existence of a minimizer is proven. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

热传导率对不同传导参数下幂律非Newton流体流经连续伸展表面时热传导的影响

在一个具有吸入/吹出功能、幂律变化的伸展表面上,分析了二维稳定非Newton流体的流动.假定热传导率按温度的线性函数变化.将控制方程无量纲化后,用Runge-Kutta法进行数值求解.将该问题的一个特例所得到的一些结果,与以前发表的结果相比较,发现两者有着很好的一致性.考虑两种情况,一种对应着致冷的表面温度,另一种对应着均匀的表面温度.数值结果显示,对上述两种情况,可变热传导参数β,传质参数d和幂律指数n,对温度分布和Nusselt数有着重大的影响.     

Heat Transfer in Rotor/Rotor and Rotor/Stator Cavity: Physics,Correlations and Numerical Modeling

The transitional and turbulent flow in the near wall sublayer is now mostly modeled based on the existing knowledge of simple 2D flows. To determine the effect of three dimensionality on the turbulent flow structures and turbulent heat transfer in the near wall areas the authors investigate numerically (SVV) turbulent flow in rotor/stator and rotor/rotor flows (with and without axial throughflow). These simple model flows contain most of the phenomena that are needed to understand more complex, 3D transitional and turbulent flows. Attention is focused on the turbulent characteristics which should have more universal character. To stabilize calculations for high Reynolds numbers (up to Re=800 000) the SVV operator is introduced into the Navier-Stokes and energy equations solver for cylindrical coordinate system without using complex numbers. Code optimization and parallelization have speeded up computations 20 times. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Stable and Accurate Numerical Method to Calculate the Motion of a Sharp Interface Between Fluids

Present address: Department of Applied Mathematics, University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001. A spectrally accurate numerical method, which is also simpleto implement, is derived to calculate the motion of a fluidinterface. A numerical instability, typical of algorithms forthis problem, is investigated via a linearizing approximationwhich shows that a trivial adjustment of the algorithm rendersit numerically stable while retaining high accuracy. To testfor the correct implementation of the algorithm, non-linearsimultaneous equations are formulated using time derivativeinformation only from the coded procedure, whose solutions describeprogressive interfacial waves of permanent form. The behaviourof this type of algorithm when variations in the point spacingoccurs along the interface is investigated and found to cause"scattering" of travelling wave modes.     

A Numerical Treatment of One-dimensional Models of Radiative Heat Transfer in Co-current Tube Furnaces

A model of a top-fired furnace, such as is used in chemicalindustrial plants, is described. The model gives rise to a systemof first-order differential equations, with boundary conditionsat both the top and bottom of the furnace. This also involvesa non-linear coupling of the radiation field to the energy ofthe gases flowing. Published accounts of this problem make useof shooting methods which converge extremely slowly. An alternativemethod will be described in which the radiative field equationsare solved by an algorithm of Grant and, to deal with the non-linearitiesof the system, a generalized Newton-Raphson method is employed.     

非线性多层渗流系统的数值方法及其应用

对多层非线性渗流系统提出适合并行计算的迎风分数步差分格式，利用变分形式、能量方法、差分算子乘积交换性、高阶差分算子的分解、先验估计的理论和技巧，得到收敛性的最佳阶的误差估计．该方法已成功的应用到油资源渗流力学运移聚集数值模拟的生产实际中．     

A Simple Analytical and Numerical Approach for Pricing Compound Options

A compound option is simply an option on an option. In this short paper, by using a martingale technique, we obtain an analytical formula for pricing compound European call options. Numerical results are given to explain some economic phenomenon.     

一种用于幂律流体流动分析的加权罚有限元法*

本文采用罚-杂交/混合有限元列式,并引用由粘度加权的连续方程的另一种摄动,建议了一种新的粘性不可压幂律流体流动分析的有限元法.提出了一个数值算例,以显示方法的有效性.     

三维非线性对流扩散问题的数值方法在渗流力学的应用

对三维非线性对流扩散问题提出一类适合并行计算的二阶迎风分数步差分格式,采用分数步技术,将三维问题化为连续解3个一维问题计算．利用变分形式、能量方法、差分算子乘积交换性、高阶差分算子的分解、微分方程先验估计的理论和技巧,得到收敛性的最佳阶的误差估计．该方法已成功的应用油资源运移聚集渗流力学数值模拟计算、海水入侵预测和防治的工程实践中．