Electromagnetic control of electroplating of a cylinder in forced convection

Continuous electrodeposition on a cylindrical cathode, e.g. electrodeposition of gold on electrical connectors, is usually characterized by an undesirable non-homogeneity of the deposit thickness. This has been observed in industrial applications. Numerical simulations have shown very good agreement with observations. This paper deals with the possibility of improving the homogeneity of the deposit thickness by a magnetic field that is parallel to the axis of the cylinder. The electromagnetic volume force generated by such a magnetic field may set up a swirling motion around the cylinder. By controlling the force density it is possible to control the thickness of the diffusive layer and consequently the mass transfer. The magnetic field can be optimized with respect to strength, spatial extent and variation with time. It is shown that a strong alternating magnetic field of low frequency gives a nearly homogeneous deposit.     

内展翅片管换热器特点及在环己酮装置中应用分析

如何提高换热器的传热系数K、提高气液热交换气体走管程的给热系数α，是换热器技术进步的一大课题。介绍了内展翅片管的结构及管程流体给热系数的计算方法，并以60kt/a环己酮工程中烷三塔塔顶气体冷凝的换热流程为例，对比了选用管壳式换热器与内展翅片管换热器的计算结果。认为选用内展翅片管换热器在技术指标和经济上都是有利的。     

A direct-forcing immersed boundary method for the thermal lattice Boltzmann method

In this study, a direct-forcing immersed boundary method (IBM) for thermal lattice Boltzmann method (TLBM) is proposed to simulate the non-isothermal flows. The direct-forcing IBM formulas for thermal equations are derived based on two TLBM models: a double-population model with a simplified thermal lattice Boltzmann equation (Model 1) and a hybrid model with an advection–diffusion equation of temperature (Model 2). As an interface scheme, which is required due to a mismatch between boundary and computational grids in the IBM, the sharp interface scheme based on second-order bilinear and linear interpolations (instead of the diffuse interface scheme, which uses discrete delta functions) is adopted to obtain the more accurate results. The proposed methods are validated through convective heat transfer problems with not only stationary but also moving boundaries – the natural convection in a square cavity with an eccentrically located cylinder and a cold particle sedimentation in an infinite channel. In terms of accuracy, the results from the IBM based on both models are comparable and show a good agreement with those from other numerical methods. In contrast, the IBM based on Model 2 is more numerically efficient than the IBM based on Model 1.     

Double-diffusive and Soret-induced convection of a micropolar fluid in a vertical channel

This paper reports an investigation of the fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel. Asymmetric temperature and concentration boundary conditions are applied to the walls of the channel. The cases of double diffusion and Soret-induced convection are both considered. The governing parameters for the problem are the buoyancy ratio and the various material parameters of the micropolar fluid. The resulting non-dimensional boundary value problem is solved analytically in closed form using MAPLE software. A numerical solution of the time dependent governing equations is demonstrated to be in good agreement with the analytical model. The influence of the governing parameters on the fluid flow as well as heat and solute transfers is demonstrated to be significant.     

重力变调作用对Rayleigh-Benard对流的影响

Rayleigh-Benard对流是研究非平衡对流的斑图(pattern)及非线性动力学特性的典型模型之一.本文通过流体力学基本方程组的数值模拟研究了二维矩形腔体中重力变调作用对RB对流中的行进波的影响,进一步研究了对流斑图结构及其非线性特性.结果表明:对流参数的变化周期依赖于重力变调作用的周期.     

考虑水的密度反转特性的二维套管自然对流模拟分析

利用热和流体流动控制方程,以温差驱动的二维同心圆环套管自然对流换热为对象,分析讨论了水在4℃附近密度反转特性对流动和传热的影响,设置了三种等温差方案,分别给出了流场和温度场,并分析了各自的传热与流动原因。分析结果表明:在不包括4℃的温度方案中,各自研究区域内均能得到一个完整的循环流动,但流动方向有所不同,同时在套管的壁面附近均存在较大的温度梯度,主流区温度梯度较小;在相同温差条件下,水的密度反转特性对于传热性能影响较大,在工程应用中,应该充分考虑水的密度反转特性。     

The relative efficiency of cryogenic fluids used in the rapid quench cooling of biological samples

The heat transfer characteristics of various cryogenic fluids used in the rapid quench cooling of biological samples are examined. It is concluded that cryofixation should be achieved during the initial plunge stage of the cooling. Liquid nitrogen maintained near its melting point of 63·1 K at a pressure in excess of the critical value of 33·5 atm will produce the quickest cooling. Nitrogen could also provide the best ultrastructure at atmospheric pressure if the minimum plunge depth and velocity criteria are satisfied. Plunging bare thermocouples into cryogenic fluids will lead to erroneous conclusions about the relative cooling efficiencies of various liquids for cryofixation. A qualitative explanation for the results obtained by Silvester et al. (1982) during the rapid cooling of water drops in various fluids is proposed.     

The vibrational behaviour of three composite beam-slab bridges

This paper describes field measurements of the vibrational frequencies of three bridges with prestressed concrete beams and in situ concrete deck slabs. In each bridge, the beams are simply supported over each span while the composite deck is continous over three or four spans with short, full width, crumple slabs between the beam diaphragms over each pier. Analytical analyses were also carried out and compared with the field measurements. Values are also given for the damping determined from the tests.     

无阻尼单自由度简谐振动临近共振情况的振幅

简谐荷载作用下的无阻尼单自由度结构系统在接近共振时 ,由以往的知识可知 ,干扰频率θ接近于系统固有频率ω ,即θ→ω的情况 ,对于结构而言是危险的 ,这是对其中的纯强迫振动进行讨论后得出的结论 ,而结构的实际情况是 ,系统并不只受到纯强迫振动。本文讨论的是考虑伴生振动和纯强迫振动两者共同作用情况下 ,无阻尼单自由度简谐振动临近共振时的振幅情况     

多年冻土地区路基工程换热分析

通过路基工程的对流、辐射换热分析 ,从对流的角度得出沿迎风面、路面的换热通量与x- 1/2 成正比 ,从而说明了路肩冻胀、滑塌等不均匀变形的原因。在一定程度上 ,对在多年冻土区的路基设计、施工有所帮助