Hydromagnetic Natural Convection from a Horizontal Porous Annulus with Heat Generation or Absorption

Journal of Engineering Physics and Thermophysics - This paper deals with a numerical study of free convection in a horizontal cylindrical annulus filled with a fluidsaturated porous medium in the...     

Formation of Structures of Multieddy Natural Convection in a Horizontal Layer Heated from Below

The Galerkin finite-element method is used to investigate the structures of supercritical thermogravitational convection in an elongated plane horizontal layer of a liquid with the Prandtl number Pr = 10. The solution of the problem with a constant heat-flux density preassigned at the lower boundary is compared to the solution of the problem for the case of boundaries at constant temperature. The results of comparative analysis of convective modes arising under different conditions at the boundaries of the layer and under different initial thermal conditions are given. The mathematical model is provided by two-dimensional unsteady-state equations for natural thermal convection in the Boussinesq approximation that are written in terms of the variables of speed eddy, stream function, and temperature.     

Numerical Study on Natural Convection of Water Near Its Density Maximum in Horizontal Annulus

In this paper, numerical simulations for natural convection of water near its maximum-density in horizontal annulus with isothermal walls are performed with the finite volume method. The results show that there are different steady-state flow patterns for different control parameters in the range of calculation for concentric horizontal annulus. Furthermore, the effects of the non-dimensional parameters, which include the radius ratio and density inversion parameter, on the temperature and flow fields are discussed, and the variation of the average Nusselt number is analyzed at different conditions. It is found that density inversion of water has a great effect on natural convective heat transfer in horizontal annulus.     

单侧受限管排自然对流的数值模拟

给出了具有 5,10,15,20 根管的管排在 103相似文献   

Marangoni and Natural Convection in a Horizontal Layer of Viscoplastic Fluid with Concentration Dependent Yield Stress. Exact Analytical Solutions

A variety of exact analytical solutions describing natural and thermocapillary convection in a horizontal single and double layer system consisting of Newtonian and viscoplastic fluids subjected to a longitudinal temperature gradient is constructed. Transport and rheological parameters of the media depend on the local concentration. A non-homogeneous concentration field is induced by mass transfer in vertical direction and by the Soret effect. The lower boundary of the system is a solid wall with no-slip, while the upper one is a free boundary. It was demonstrated that, depending on the governing parameters of the system, a viscoplastic layer may be entirely or partially yielded or completely unyielded. If the yield stress is the function of concentration, the latter determines positions of yielded and unyielded regions. The dependence of the flow patterns (appearance and position of unyielded regions), velocity profile and mass and heat transfer rate on the governing parameters have been studied. Special attention was paid to the effect of concentration dependence of the yield stress and to the Soret effect.     

Heat Transfer at Mixed Convection in Horizontal Flat Channels of the Vacuum Vessel of the International Thermonuclear Experimental Reactor (ITER)

The results are given of the experimental investigation of the intensity of heat transfer from the flat horizontal surfaces of a model of the vacuum vessel channel of the international thermonuclear experimental reactor (ITER). The channel height is varied from 12 to 50 mm, as well as its heated length (1.02 and 2.48 m). The water flow velocities of 0.0066 to 0.15 m/s correspond to the values of Re $equals; 560 to 16 600. The specific heat flux on the heat-transfer surfaces is 1.3–24.4 kW/m². The examined range of parameters is characterized by a significant temperature stratification of water over the channel height. Generalizing relationships are suggested based on the experimental results.     

封闭腔内纳米流体自然对流换热的数值模拟

采用数值模拟方式研究充满了纳米流体的封闭腔内的稳态自然对流。重点分析了纳米颗粒的体积分数,Ra数以及不同类型纳米颗粒对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;对于给定的Ra数下,随着纳米流体的体积分数增大,纳米流体换热效果显著增强;对于给定的体积分数下,随着Ra数增大,纳米流体的换热强度也随之增大,并且换热机理由热传导为主变为热对流为主;通过Ag,Cu,CuO和Al2O3四种纳米颗粒的对流换热效果比较分析得出,金属Ag和Cu纳米颗粒比金属氧化物CuO和Al2O3的纳米颗粒制备的纳米流体的对流换热效果更好。     

倾斜方腔内纳米流体自然对流的数值研究

对充满Cu-水纳米流体的二维倾斜方腔内的自然对流换热进行了数值研究,研究了纳米颗粒体积份额φ、Ra数和腔体倾角对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;在一定的腔体倾角φ下,增大Ra均可以强化腔体内的自然对流换热,而且随Ra数的增大,强化效果越强;当Ra=104时,对不同的腔体倾角,纳米流体对换热强度提高的比例大致相当。     

Plasma Electron Source with a Beam of Large Cross Section

We present the design and characteristics of a plasma electron source based on a discharge in crossed E × H fields, which provides the formation of technological highenergy beams with a large cross section in steadystate and pulsed regimes, and consider conditions for excitation of a highcurrent anomalous glow discharge forming an emitting plasma in a pulsed regime.     

聚苯胺纳米矩形管的制备与表征

以樟脑磺酸(CSA)为掺杂剂、过硫酸铵为氧化剂.在水溶液体系中通过苯胺原位聚合制得直径为300～600nm的聚苯胺纳米矩形管,其导电率为0.1～1S/cm.通过扫描电镜(SEM)和透射电镜(TEM)对产物的形貌进行表征.发现n(CSA)/n(ANi)将影响产物的形貌.利用傅立叶红外光谱(FT-IR)和紫外一可见光谱(Uv_vis)对聚苯胺分子结构进行表征,发现产物是质子化掺杂的聚苯胺.通过X射线衍射(XRD)分析发现,聚苯胺纳米矩形管比纤维结构具有更好的分子链排列规整性.     

倾斜角度对封闭方腔内液体自然对流的影响

在多种倾斜角度下,对封闭腔内液体进行了数值模拟。重点分析了Ra数变化和倾斜角度对对流传热的影响。研究表明：随着Ra数的增大,换热由热传导为主转化为对流换热为主;倾斜角度对Nu数的变化影响很大,并且当倾斜角度处于90o～135o时,Nu数可以达到最大值。     

Statistical Modeling of Thermal‐Radiation Transfer in Natural‐Convection Turbulent Diffusion Flames. 1. Model Construction

Methods of calculation of radiation transfer, which are used in modeling turbulent diffusion flames, are analyzed. Realization of the statistical method (Monte Carlo method) in combination with the equations of turbulent flow and combustion of a multicomponent mixture which is formed in combustion of hydrocarbons in air is presented. A method of calculation of the effective coefficient of absorption for a mixture of absorbing gases and soot is described. The effect of turbulent temperature fluctuations on the emission of thermal radiation is taken into account.     

Analysis of Nonstationary Incompressible Flows in Differently Shaped Channels on the Basis of Symmetries

Nonstationary flows in laminar and turbulent regimes in differently shaped channels have been investigated theoretically. An approach has been used which is based on the properties of the symmetry of differential equations (Lie groups) that describe the process of an accelerated channel flow. A way in which the self-similar forms of one-dimensional and two-dimensional flow can be obtained on the basis of symmetries is shown. The self-similar equations of the process and their analytical and numerical solutions are given.     

Natural Convection of Water in an Inclined Three-Dimensional Rectangular Cavity in the Vicinity of the Density Inversion Point

The Navier–Stokes equations in the Boussinesq approximation in view of the temperature dependence of thermal parameters are used to perform a numerical investigation of the stationary process of natural convection of water in an inclined closed three-dimensional rectangular cavity in the vicinity of 4°C. The forms of stationary convective flows are determined; the effect of the Grashof number, of the geometric dimensions of the cavity, of the slope angle, and of the inversion of liquid density on the process of heat transfer is investigated. A comparison is made with the results of calculations performed on the basis of two-dimensional flow equations.     

钢筋混凝土方形烟囱的控爆拆除

本文根据方形烟囱的受力特点,结合实例,分析了烟囱的爆破特点与方法。     

铸件凝固过程的宏观及微观模拟仿真研究进展

面向市场经济,迎接全球化竞争的挑战,为国民经济的发展作贡献,就要十分重视制造业特别是铸造行业的发展。但是,我国铸造行业与国外相比有很大差距,它制约着国民经济的发展。世界各国在铸造成形加工技术的发展趋势方面,认识是一致的,即：一是大型工程中特大型铸件的关键铸造技术;二是向精确成形技术方向发展;三是用计算机模拟仿真逐步代替传统的经验性研究方法。铸造过程计算机模拟仿真是改造传统铸造产业的必由之路,是当今世界各国专家学关注的热点。铸造充型凝固过程的数值模拟可以帮助工程技术人员优化工艺设计,缩短试制周期、降低生产成本、确保铸件质量,已成为铸造领域最热门的研究课题之一。目前,凝固过程的流场、温度场数值模拟及缩孔缩松预测已应用于实际生产,应力分析、微观组织模拟等方面的基础研究及实用化进程都取得了很大进展。     

The Weight Loss Effect of Heated Inner Cylinder by Free Convection in Horizontal Cylindrical Enclosure

The work presents results of numerical simulations of natural convection in cavity formed by the surfaces of two horizontal coaxial cylinders. The temperature of the outer cylinder is constant. The area between the cylinders is filled with an ideal incompressible fluid. The inner cylinder is set as the heater. The solution of the equations of thermal convection in a two-dimensional approximation performed by the software package ANSYS Fluent with finite volume method. The study compares the results of numerical simulation with several well-known theoretical and experimental results. The nature of interaction of the inner cylinder with a convection current created in the gap was observed. It was shown that the flux appeared around a heated cylinder affects the weight of the heat source and causes an additional lift force from the surrounding fluid. The various Rayleigh numbers (from 1.0 ? 10³ to 1.5 ? 10⁶) and fluid with different Prandtl number (from 0.5 to 1.0 ? 10⁵) are considered.     

Validation of the Thermal Equilibrium Assumption in Periodic Natural Convection in Porous Domains

The validity of the local thermal equilibrium assumption in the periodic free convection channel flow is investigated analytically. Two cases are considered where in the first case transverse conduction in the solid domain is included while in the second case transverse conduction in the fluid domain is included. The periodic disturbance in the free convection flow is due to a periodic thermal disturbance imposed on the channel walls. The Darcy–Brinkman model is used to model the flow inside the porous domain. It is found that four dimensionless parameters control the local thermal equilibrium assumption in the first case and five parameters control the local equilibrium assumption in the second case. The criteria that secure the validity of the local thermal equilibrium assumption are derived.     

带有横向调度的易变质商品两级库存系统分析与优化

在对库存控制策略研究的基础上,针对一对多的易变质商品两级库存系统,在需求率、变质率随时间变化和二级库存之间存在横向调度的情况下,建立了一对多的易变质商品两级库存优化数学模型,提出了基于牛顿法的求解算法,得出了在一定时间水平上的两级库存系统的最优控制策略。通过算例仿真验证了模型的正确性和求解算法的有效性。分析了两级库存控制参数与补货周期、系统总成本的关系,结果表明:在二级库存之间的横向调度不仅可以缩短补货周期,还可以有效降低库存系统的总成本;变质率的增加使得极大库存水平的波动加剧。