Wavenumber Selection by Bénard-Marangoni Convection at High Supercritical Number

Marangoni Benard convection, which is mainly driven by the thermocapillary （Marangoni） effect, occurs in a thin liquid layer heated uniformly from the bottom. The wavenumber of supercritical convection is studied experimentally in a 160×160-mm^2 cavity that ＆ heated from the bottom block. The convection pattern ＆ visualized by an infrared thermography camera. It is shown that the onset of the Benard cell is consistent with theoretical analysis. The wavenumber decreases obviously with increasing temperature, except for a slight increase near the onset. The wavenumber gradually approaches the minimum when the supercritical number e is larger than 10. Finally, a formula is devised to describe the wavenumber selection in supercritical convection.

Penetrative Bénard-Marangoni Convection in a Micropolar Ferrofluid Layer via Internal Heating and Submitted to a Robin Thermal Boundary Conditions

Penetrative Bénard-Maranagoni convection in micropolar ferromagnetic fluid layer in the presence of a uniform vertical magnetic field has been investigated via internal heating model. The lower boundary is considered to be rigid at constant temperature, while the upper boundary free open to the atmosphere is flat and subject to a convective surface boundary condition. The resulting eigenvalue problem is solved numerically by Galerkin method. The stability of the system is found to be dependent on the dimensionless internal heat source strength Ns, magnetic parameter M1, the non-linearity of magnetization parameter M3, coupling parameter N1, spin diffusion parameter N3 and micropolar heat conduction parameter N5. The results show that the onset of ferroconvection is delayed with an increase in N1 and N5 but hastens the onset of ferroconvection with an increase in M1, M3, N3 and Ns. The dimension of ferroconvection cells increases when there is an increase in M3, N1, N5 and Ns and decrease in M1 and N3.

Exponential B-Spline Solution of Convection-Diffusion Equations

We present an exponential B-spline collocation method for solving convection-diffusion equation with Dirichlet’s type boundary conditions. The method is based on the Crank-Nicolson formulation for time integration and exponential B-spline functions for space integration. Using the Von Neumann method, the proposed method is shown to be unconditionally stable. Numerical experiments have been conducted to demonstrate the accuracy of the current algorithm with relatively minimal computational effort. The results showed that use of the present approach in the simulation is very applicable for the solution of convection-diffusion equation. The current results are also seen to be more accurate than some results given in the literature. The proposed algorithm is seen to be very good alternatives to existing approaches for such physical applications.

Nonlinear three-dimensional stretched flow of an Oldroyd-B fluid with convective condition, thermal radiation, and mixed convection

The effect of non-linear convection in a laminar three-dimensional Oldroyd-B fluid flow is addressed. The heat transfer phenomenon is explored by considering the non-linear thermal radiation and heat generation/absorption. The boundary layer as- sumptions are taken into account to govern the mathematical model of the flow analy- sis. Some suitable similarity variables are introduced to transform the partial differen- tial equations into ordinary differential systems. fifth-order techniques with the shooting method The Runge-Kutta-Fehlberg fourth- and are used to obtain the solutions of the dimensionless velocities and temperature. The effects of various physical parameters on the fluid velocities and temperature are plotted and examined. A comparison with the exact and homotopy perturbation solutions is made for the viscous fluid case, and an excellent match is noted. The numerical values of the wall shear stresses and the heat transfer rate at the wall are tabulated and investigated. The enhancement in the values of the Deborah number shows a reverse behavior on the liquid velocities. The results show that the temperature and the thermal boundary layer are reduced when the non- linear convection parameter increases. The values of the Nusselt number are higher in the non-linear radiation situation than those in the linear radiation situation.

CONVECTION AND MASS TRANSFER IN LASER CLADDING ON FeCrSiB ALLOY

The convection patterns were observed in laser cladding layer of FeCrSiB alloy.Laser beam symmetry, dilution of cladding layer from substrate,etc.With relation to con- vection patterns have been investigated.Macro-segregation and macroalloying in the cladding layer were found to be resulted from convection.The dilution rates of substrate materials into cladding layer are directly influential in microstructure and performace of the cladding.Ideal laser cladding conditions require that there is a minimum of dilution.

Stability of buoyancy-driven convection in an Oldroyd-B fluid-saturated anisotropic porous layer

The nonlinear stability of thermal convection in a layer of an Oldroyd-B fluid-saturated Darcy porous medium with anisotropic permeability and thermal diffu- sivity is investigated with the perturbation method. A modified Darcy-Oldroyd model is used to describe the flow in a layer of an anisotropic porous medium. The results of the linear instability theory are delineated. The thresholds for the stationary and oscillatory convection boundaries are established, and the crossover boundary between them is de- marcated by identifying a codimension-two point in the viscoelastic parameter plane. The stability of the stationary and oscillatory bifurcating solutions is analyzed by deriving the cubic Landau equations. It shows that these solutions always bifurcate supercritically. The heat transfer is estimated in terms of the Nusselt number for the stationary and oscillatory modes. The result shows that, when the ratio of the thermal to mechanical anisotropy parameters increases, the heat transfer decreases.

Bnard-Marangoni对流温度振荡转捩实验研究

主要通过实验观测Benard-Marangoni对流中存在的温度振荡现象,研究了温度振荡的起振临界Ma数,以及初步探讨了温度振荡随Ma数增加的转捩过程.实验结果表明不同物性参数的硅油温度振荡临界Ma数满足同一临界条件.不同的物性参数的介质表现出不同的温度振荡转捩过程,但同一物性参数不同厚度的介质表现相同的振荡规律.此外,还用粒子迹线法观察了流场结构及转捩过程.

两层液体Bénard-Marangoni对流的实验研究

采用粒子图像测速技术(PIV)对两层流体Bénard-Marangoni对流进行了实验研究.研究了各种不同厚度比下的临界对流模式,同时研究了在温差变大时向超临界对流模式转化过程.实验结果表明,界面张力对各种对流模式的形成和转变具有重要的作用.

两层液体Bénard-Marangoni对流的界面张力效应

采用PIV技术对两层流体Bénard-Marangoni对流进行了实验研究,得到了不同厚度比下的速度场,分析了界面张力在各种对流模式中的作用。和Rayleig-Bénard对流的三种临界对流模式相比,由于界面张力对上下层浮力对流的不同作用效果,使得更复杂的临界对流模式在Bénard-Marangoni对流体系中出现;在实验中首次观测到三层涡胞结构等现象。

三维模型液滴蒸发的Bénard-Marangoni对流模拟

现有液滴的数值模拟多为二维模型,难以与实验观察到的Bénard-Marangoni对流现象进行比较说明。因此考虑液滴蒸发的冷却效应,通过建立三维的液滴蒸发模型,模拟恒接触角模式液滴在加热基板上的蒸发过程,研究Bénard-Marangoni涡胞的变化,Ma数对Bénard-Marangoni涡胞产生的影响。当Ma数大于临界Ma数时,液滴出现Bénard-Marangoni涡胞,并处于不稳定状态,涡胞不断出现、消失,液滴的滞止点在蒸发过程中不维持在液滴中心位置,直至液滴趋于稳定。在低接触角时,液滴出现Bénard-Marangoni涡胞所需的临界Ma值较小,随着接触角增大,液滴出现Bénard-Marangoni涡胞所需临界Ma呈线性增加。当接触半径一致时,液滴蒸发趋于稳定时的Bénard-Marangoni涡胞随Ma数的增加而增加;当基板温度与液滴温差一定时,液滴蒸发趋于稳定时的Bénard-Marangoni涡胞随液滴接触半径的增加而增加。

Heat transfer analysis in the flow of Walters' B fluid with a convective boundary condition

Radiative heat transfer in the steady two-dimensional flow of Walters＇ B fluid with a non-uniform heat source/sink is investigated. An incompressible fluid is bounded by a stretching porous surface. The convective boundary condition is used for the thermal boundary layer problem. The relevant equations are first simplified under usual boundary layer assumptions and then transformed into a similar form by suitable transformations. Explicit series solutions of velocity and temperature are derived by the homotopy analysis method （HAM）. The dimensionless velocity and temperature gradients at the wall are calculated and discussed.

Three-dimensional flow of Oldroyd-B fluid over surface with convective boundary conditions

The present study addresses the three-dimensional flow of an Oldroyd-B fluid over a stretching surface with convective boundary conditions. The problem formulation is presented using the conservation laws of mass, momentum, and energy. The solutions to the dimensionless problems are computed. The convergence of series solutions by the homotopy analysis method （HAM） is discussed graphically and numerically. The graphs are plotted for various parameters of the temperature profile. The series solutions are verified by providing a comparison in a limiting case. The numerical values of the local Nusselt number are analyzed.

求解对流扩散方程的混合三次B-样条配点法

通过对三次B-样条和三次三角B-样条基函数引入权因子ω,给出了对流扩散方程的混合三次B-样条配点法。对对流扩散方程空间离散采用混合三次B-样条配点法和时间离散采用向前有限差分,引入参数θ,建立差分格式。对差分格式的稳定性进行分析,得到稳定性条件。数值实验表明所构造方法的有效性,并且适当调整权因子ω和参数θ的值,可提高计算的精度。

基于B样条函数的对流扩散方程数值模拟

利用三次B样条函数,构造了一个求解对流扩散问题的隐式格式,并分析了算法误差及稳定性,给出了数值例子.数值结果表明,构造的格式能处理文献[2]中格式不能处理的问题,且精度更高。

纳米多孔CuO对硼基铝热剂药线燃烧性能的影响

为研究多孔Cu O对B/Cu O药线燃烧性能的影响,选用多孔、立方和针状Cu O分别与无定型硼进行微观复合,借助微笔直写技术制得相应配方的药线。使用流变仪对油墨的动态粘度进行测试,通过高速摄影技术测试药线的线性燃速,并采用扫描电镜、X射线衍射装置对固体反应物、产物进行测试。结果表明:借助微笔直写技术制得的B/Cu O药线中各组分分布均匀、燃烧性能稳定;多孔Cu O的加入最高可将B/Cu O药线的燃烧速度提升300%,氧化物形貌的改变并不会改变B/Cu O的反应进程,多孔Cu O的加入提高了药线反应过程中的热对流,从而提升了药线的燃烧性能。

基于五次B样条的对流-扩散方程数值解法

基于五次B样条函数,提出一种求解对流-扩散方程的五次B样条方法。先利用光滑余因子协调法,给出有界闭区间上的具有均匀节点的五次B样条基函数表达式。接着计算在有界闭区间两端点处具有重节点的B样条基函数表达式。最后,将五次B样条基函数应用于求解一类对流扩散方程,在此过程中,按时间步长τ对对流-扩散方程进行离散,建立五次B样条逼近格式,由此提升数值方法的精度。

新型独立B型液化天然气船围护系统及蒸发率计算

以一艘17万立方米新型独立B型液化天然气(LNG)船为研究对象,将该型围护系统与传统薄膜型和MOSS独立球型围护系统进行详细对比,突出该型围护系统的特点;分析船体和舱室结构后,通过合理和必要的简化,提供了一种计算独立B型液货舱传热的方法,通过数值模拟计算不同工况条件下液货舱的蒸发率,研究了聚氨酯泡沫绝热材料的热导率变化对液货舱蒸发率的影响。得到以下结论:(1)新型独立B型围护系统与传统围护系统相比有突出优势,在将来有很好的应用前景;(2)绝热层厚度为450 mm时,为了满足日蒸发率不能超过0.1%的限定要求,所选用的绝热材料的热导率应当小于或等于0.03 W·m-1·K-1。

对流-扩散方程数值解的四次B样条方法

基于四次B样条函数,提出一种求解一类对流-扩散方程的四次B样条方法。首先利用光滑余因子协调法,得到有界闭区间上具有均匀节点的一元四次B样条基函数表达式。接着计算在有界闭区间两端点处具有重节点的几种不同情况下的B样条基函数表达式,这些样条基函数具有非负性、单位分解性等良好的性质。然后将一元四次B样条函数应用于求解一类一维对流-扩散方程,其中对于对流-扩散方程的离散过程,对于时间变量的离散采用向前有限差分,而对于空间变量的离散,引入参数δ,建立四次样条逼近格式。之后利用四次B样条函数去求解该对流-扩散方程。最后通过具体算例,将四次样条逼近方法与有限差分方法进行比较,且给出直观的数值误差对比,由此说明样条逼近方法更加简便实用。

独立B型液化天然气运输船绝热层局部失效对结构安全的影响

根据独立B(SPB)型液化天然气(LNG)运输船绝热层失效后船体的传热特点,提出通过温度影响因子和面积影响因子分析船体结构温度场和内层对流空间空气温度场的耦合关系.选取液舱绝热层典型的局部失效模式,采用计算流体动力学(CFD)数值模拟和有限元分析求解失效前后船体温度场和温度应力,分析了绝热层局部失效对船体结构安全性的影响.对事故工况下SPB型LNG船的安全性评估具有一定的参考意义.

B型独立液货舱LNG船的温度场分布

以170 000m^3 B型独立液货舱LNG船为研究对象,基于热力学方法,通过液货舱传热模型的合理简化及流换热系数的数值迭代计算,针对该B型独立液货舱LNG船进行稳态温度场分析。依据温度场分布进行货舱区船体结构钢级选择,并进一步研究外界环境温度和装载工况对整个货舱区船体温度场分布的影响,从而为B型独立液货舱以及类似LNG船液货舱结构设计提供指导。