多孔饱和矩形管中粘性随温度变化对熵产、热和流体流动的影响

研究了充填流体-饱和多孔介质的矩形管中,随温度变化的粘性对充分发展强迫对流的影响.采用Darcy流动模型并假设粘性-温度为倒线性关系.管壁视为均匀热通量,即Kays和Craw-ford称为的H边界条件.当流体粘性随温度升高而降低时,管壁的Nusselt数增大.求解速度和温度分布时,利用热力学第二定律求解了局部平均熵产率.根据Brinkman数、Péclet数、粘性变化数、无量纲管壁热通量和管道截面宽高比,给出了熵产率、Bejan数、传热不可逆性和流体流动不可逆性的表达式.这些表达式是该类问题参数研究的基础.可以看出,当管道截面宽高比的增大使熵产率减小时,方形管中流动产生的熵大于矩形管,这类似于Ratts和Raut研究的明流(clear flow)情况.     

微极流体向受热面的MHD驻点流动

分析了有均匀横向磁场作用时,导电微极流体垂直冲击受热面时形成的二维驻点流动问题．应用适当的相似转换,将连续、动量、角动量及热量的控制方程,及其相应的边界条件,简化为无量纲形式．然后,利用以有限差分离散化为基础的算法,求解简化了的自相似非线性方程．用Richardson外推法,进一步求精其结果．以图表形式表示磁场参数、微极性参数、Prandtl数对流动和温度场的影响,说明了其解的重要特性．研究表明,随着磁场参数的增大,速度和热边界层厚度变小了．与Newton流体相比较,微极流体的剪应力和传热率出现明显的减少,这对聚合物生产过程中流体的流动和热量控制是有益的．     

流体饱和多孔介质中热发展强迫对流的熵产分析

利用Darcy流动模型,同时考虑粘性耗散效应,分析研究了以两等温平板为边界的多孔介质中,热发展强迫对流的熵产.参数研究表明,组参数和Péclet数减小,而Brinkman数增大时,熵产增大.形象化的热线表示方法着重应用于Br＜0的情况,在这种情况下,在顺流的某些位置上,存在热传递方向的改变,即从原来的壁面向外传热变为向壁面传热.     

电渗流中传热传质过程与熵的分析

在壁面存在恒定热通量条件下,分析微通道内电渗流中传热传质过程与熵的生成.建立数值计算模型,分别采用Poisson-Boltzmann方程、Navier-Stokes方程、Nernst-Planck方程和能量方程来描述微通道内双电层电势、流场、离子浓度和温度的分布情况.引入熵产生,进一步研究不同流动参数对流体传热过程的作用,讨论不同流动参数下各热效应的变化规律,并具体分析热效应参数对流体总熵增加及各部分热效应对总熵比重的影响.结果表明,动电参数与Joule(焦耳)热系数的增大会使得传热性能减弱,动电参数对传热性能影响更为明显;流体的总熵为动电参数、传质系数和质量弥散系数的增函数.     

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．     

可渗透收缩薄膜引起的三维不稳定边界层流动

研究可渗透收缩薄膜上的不稳定粘性流动．通过相似变换得到相似方程．在不同的不稳定参数、质量吸入参数、收缩参数、Prandtl数下,数值地求解相似方程,得到速度和温度的分布,以及表面摩擦因数和Nusselt数等．结果发现,与不稳定的伸展薄膜不同,在质量吸入参数和不稳定参数的某一范围内,可渗透收缩薄膜上的不稳定流动存在双重解．     

柱黑洞的熵

采用由广义测不准关系得到的新的态密度方程,研究了具有柱对称时空背景下黑柱的 熵．利用新的态密度方程后,不通过截断可以消除brick-wall模型中无法克服的发散项,并且 同样可得到黑柱的熵与视界面积成正比的结论．计算结果表明,黑柱熵是视界面上量子态的 熵,是一种量子效应,是黑洞的内禀性质．在计算中我们直接应用量子统计的方法,求柱黑洞 背景下玻色场与费米场的配分函数,避开了求解各种粒子波动方程的困难,为研究各种时空黑 洞熵提供了一条简捷的新途经．     

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.     

三维泊松方程基于Richardson外推法的高阶紧致差分方法

基于Richardson外推法提出了数值求解三维泊松方程的高阶紧致差分方法.方法通过利用四阶和六阶紧致差分格式,分别在细网格和粗网格上求解,然后利用Richardson外推技术和算子插值方法,得到三维泊松方程在细网格上的六阶和八阶精度的数值解.数值实验结果验证了该方法的精确性和有效性.     

非Newton流体在多孔介质中沿竖直面作自由对流时应力屈服和Soret效应对其传热/传质的影响

对饱和的非Newton幂律流体,流经多孔介质中竖直平板时的自由对流,在出现应力屈服和Soret效应时,研究化学反映对传热/传质的影响.用相似变换,将边界层控制方程及其边界条件转换为无量纲的形式,然后通过有限差分法求解该方程.给出并讨论了浓度曲线,以及本问题各种参数值时的Nusselt数和Sherwood数.发现化学反应参数γ、化学反应级m、Soret数Sr、浮力比N、Lewis数Le及无量纲流变参数Ω对流场有着显著的影响.     

Entropy generation under the effect of suction/injection

This work investigates entropy generation in a steady flow of viscous incompressible fluids between two infinite parallel porous plates. The fluid temperature variation is due to asymmetric heating of the porous plates as well as viscous dissipation. Two different physical situations are discussed with their entropy generation profiles: (i) Couette flow with suction/injection and (ii) pressure-driven Poiseuille flow with suction/injection. In each case, closed form expressions for entropy generation number and Bejan number are derived in dimensionless form by using the expressions for velocity and temperature which are derived by solving the resulting momentum and energy equations by the method of undetermined coefficient. The effect of the governing parameters on velocity, temperature, entropy generation and Bejan number are extensively discussed with the help of graphs. It is interesting to remark that entropy generation number increases with suction on one porous plate while it decreases on the other porous plate with injection.     

Entropy generation in nanofluid flow of Walters-B fluid with homogeneous-heterogeneous reactions

Research on optimization of entropy generation in nanofluid flow gained much interest. In this study, the Walter's-B nanofluid flow is considered to analyze the irreversibility in cubic autocatalysis. Fluid motion is considered in presence of viscous dissipation, magnetohydrodynamics (MHD), radiation, and heat generation absorption. Homotopy analysis method (HAM) is employed to solve nonlinear ordinary differential system. Results show that fluid flow reduces for larger Weissenberg and Hartman numbers. Temperature gradually enhances for larger Weissenberg number and radiation parameter. For higher estimation of thermophoresis parameter, the temperature and concentration are enhanced. Opposite impact of Hartman and Weissenberg numbers is noticed for entropy generation and Bejan number. Disorderedness and Bejan number are reduced near the sheet, while the opposite trend is seen away from the sheet.     

Effect of variable viscosity and viscous dissipation on the Hagen‐Poiseuille flow and entropy generation

In this article, the steady‐state flow of a Hagen‐Poiseuille modelin a circular pipe is considered and entropy generation due tofluid friction and heat transfer is examined. Because of variationin fluid viscosity, the entropy generation in the flow varies. Inhis model, Arrhenius law is applied for temperature equation‐dependent viscosity, and the influence of viscosity parameters on the entropy generation number and distribution of temperature and velocity is investigated. The governing momentum and energy equations, which are coupled due to the dissipative term in the energy equation, were solved by analytical techniques. The solutions of equations via perturbation method and homotopy perturbation method are obtained and then compared with those of numerical solutions. It is found that the fluid viscosity influences considerably the temperature distribution in the fluid close to the pipe wall, and increasing pipe wall temperature enhances the rate of entropy generation. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 27: 529–540, 2011     

Microorganisms swimming through radiative Sutterby nanofluid over stretchable cylinder: Hydrodynamic effect

In the present article, radiative Sutterby nanofluid flow over a stretchable cylinder is considered. The suspended swimming microorganisms have been deliberated in the fluid analysis. Different processes such as Brownian motion, thermophoresis, Joules heating, and viscous dissipation have been inspected in the presences of stratification parameters. The solutions for flow profiles have been obtained via optimal homotopy analysis method. Impacts of different physical involved variables on non-dimensional velocity, temperature, nanofluid concentration, and concentration of density of swimming microorganisms have been debated. Coefficient of skin friction, local Nusselt number, Sherwood number, and density of motile organisms have been calculated. The results reveal that Sutterby fluid parameter enhances the skin friction and has a reverse impact on the velocity, while an increase in stratification causes a declination in the flow boundary layers. The temperature of the flow is also seen to be boosted by the increment in Brownian motion parameter. Analysis of entropy generation shows that the concentration difference parameter maximizes the entropy and minimizes the dimensionless Bejan number.     

Effects of variable viscosity on non-Darcy MHD free convection along a non-isothermal vertical surface in a thermally stratified porous medium

An analysis is performed for non-Darcy free convection flow of an electrically conducting fluid over an impermeable vertical plate embedded in a thermally stratified, fluid saturated porous medium for the case of power-law surface temperature. The present work examines the effects of non-Darcian flow phenomena, variable viscosity, Hartmann–Darcy number and thermal stratification on free convective transport and demonstrates the variation in heat transfer prediction based on three different flow models. The wall effect on porosity variation is approximated by an exponential function. The effects of thermal dispersion and variable stagnant thermal conductivity are taken into consideration in the energy equation. The resulting non-similar system of equations is solved using a finite difference method. Results are presented for velocity, temperature profiles and local Nusselt number for representative values of different controlling parameters.     

Homotopy analysis method for the heat transfer in a asymmetric porous channel with an expanding or contracting wall

The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the porous upper plate is investigated and an analysis is made to determine the heat and mass transfer. The unsteady Navier–Stokes equations are reduced to a generalization of the Proudman–Johnson equation retaining the effect of wall motion using a suitable similarity transformation. The analytical solution for stream function and heat transfer characteristics are obtained by employing homotopy analysis method. The effects of various physical parameters like expansion ratio, Prandtl number, Reynolds number on various momentum and heat transfer characteristics are discussed in detail.     

Heat transfer in MHD viscoelastic boundary layer flow over a stretching sheet with non-uniform heat source/sink

This paper presents the study of momentum and heat transfer characteristics in a hydromagnetic flow of viscoelastic liquid over a stretching sheet with non-uniform heat source, where the flow is generated due to a linear stretching of the sheet and influenced by uniform magnetic field applied vertically. Here an analysis has been carried out to study the effect of magnetic field on the visco-elastic liquid flow and heat transfer over a stretching sheet with non-uniform heat source. The non-linear boundary layer equation for momentum is converted into ordinary differential equation by means of similarity transformation and is solved exactly. Heat transfer differential equation is also solved analytically. The effect of magnetic field on velocity, skin friction and temperature profiles are presented graphically and discussed.     

Al2O3-47 nm and Al2O3-36 nm characterizations of nonlinear differential equations for biomedical applications: Magnetized peristaltic transport

Current research models the Al₂O₃ 47nm and Al₂O₃ 36nm nanoparticles transportation through peristalsis with entropy optimization. Conservation laws for mass, momentum and energy are used to model the present flow situation. These equations elaborates the magnetohydrodynamics, Hall, thermal radiation, Joule heating, heat generation and absorption. Convective heat transfer impacts are studied at channel walls. Entropy is modeled in view of thermodynamics second law. Two different expressions for effective viscosity are accounted. Simplification of the modeled equations is done through lubrication assumptions. Solution for momentum equation is obtained analytically and for numerically for temperature equation. Built-in shooting procedure is utilized to obtain the desired numerical results. Later on these obtained results are used to sketch and discussed the flow quantities of interest for the influential parameters accounted in the problem.     

Heat transfer enhancement for boundary layer flow over a wedge by the use of electric fields

The effect of an electric field is investigated for heat transfer properties in a laminar, incompressible, non-isothermal boundary layer gas flow over a wedge. The governing boundary layer equations are reduced to an ordinary differential equation system using similarity transformations. The reduced equations are solved numerically for different values of electric and flow field parameters characterizing the ratio of electric force to fluid inertia force, Joule heating and ion kinetic work. For specific electric field function forms, leading to similarity solutions, velocity boundary layers are observed to become thinner and heat transfer properties are shown to be enhanced near the wall. The level of enhancement is controlled by the electric body force with additional effects of Joule heating and ion kinetic work on the bulk flow. The effects of low and high Prandtl numbers are also demonstrated. Heat transfer enhancement is observed to increase with increasing Prandtl number.