微重力环境下Marangoni对流的有限元数值模拟

本文以悬浮区为背景研究液桥中气液交界面上由表面张力所驱动的流体对流。我们采用有限元方法对轴对称、定常运动方程,能量方程,自由面切向、法向应力平衡条件迭代求解,首次考虑了边界形状的影响,得到了自洽的流区位形和流场、温度场、表面压强分布。一般说来,流区自由面呈弯月形。结果表明,只要表面张力数 C_a<1,静态平衡的流区位形就是动态情况的良好近似。本文还分析了C_a数及G_r 数对流区位形的影响,得到了不同 M_a 数及散热条件下的温度场和流函数分布。     

A survey of experimental heat transfer data for nucleate pool boiling of liquid metals and a new correlation

The experimental data for heat transfer during nucleate pool boiling of saturated liquid metals on plain surfaces are surveyed and a new correlation is presented. The correlation is h = Cq^0.7p_r^m, where C and m are, respectively, 13.7 and 0.22 p_r < 0.001 and 6.9 and 0.12 for p_r > 0.001 (h is in W/m² K and q in W/m²). This correlation has been verified with data for K, Na, Cs, Li, and Hg from 17 sources over the reduced pressure (p_r) range of 4.3 × 10⁻⁶ to 1.8 × 10⁻². The correlation of Subbotin et al. was found unsatisfactory, but a modified correlation was developed that also gives good agreement with most of the data.     

Silicon transport under rotating and combined magnetic fields in liquid phase diffusion growth of SiGe

The effect of applied rotating and combined (rotating and static) magnetic fields on silicon transport during the liquid phase diffusion growth of SiGe was experimentally studied. 72‐hour growth periods produced some single crystal sections. Single and polycrystalline sections of the processed samples were examined for silicon composition. Results show that the application of a rotating magnetic field enhances silicon transport in the melt. It also has a slight positive effect on flattening the initial growth interface. For comparison, growth experiments were also conducted under combined (rotating and static) magnetic fields. The processed samples revealed that the addition of static field altered the thermal characteristics of the system significantly and led to a complete melt back of the germanium seed. Silicon transport in the melt was also enhanced under combined fields compared with experiments with no magnetic field. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

高速气流中激光加热平板数值模拟与分析

 采用流固耦合方法,数值模拟了高速流场中激光作用下来流速度对平板温度分布的影响。结果表明:无激光辐照时,高速气流中平板有较高的气动生热平衡温度,且平板-气流之间的换热系数随来流速度增大而增大;在平板前沿换热系数增长最快,沿平板长度方向增速趋于平缓。分析了激光辐照时高速气流中激光加热平板的温度分布情况,考察了来流速度不同时,气动生热、散热和激光辐照对平板温度的影响,给出了激光辐照后的温升情况和温度分布,分析了在不同速度来流下,对流散热、摩擦生热和激光加热之间的竞争关系,结果表明,平板温度具体分布主要是加热过程竞争的结果。     

无沸腾喷雾冷却技术的研究进展

文中简述了无沸腾喷雾冷却技术近年来国内外的研究进展。着重介绍了关于影响无沸腾区换热各参数的实验研究,如壁面温度、介质体积通量、喷雾流量、喷雾倾角和喷雾高度等,为寻求最佳换热提供了指导。并对无沸腾区的理论研究内容进行了归纳,主要是模拟不同喷雾条件下的换热过程及特性参数(如液膜厚度)的大小和分布,并将理论值与实验数据进行比较分析;总结了影响无沸腾区换热的喷雾特性参数和外部特性。     

随机对流扩散方程的数值仿真

本文针对对流一扩散随机过程在随机输入（即随机输运和源项）,作用下进行数值仿真。我们先将对流扩散随机微分方程中的随机函数采用有限项截断的多项式浑沌展开（Polynomial Chaos Expansion）展开,再由Galerkin映射法得到求解浑沌展开系数的确定性方程组。这是一个在物理空间包含多尺度解的大方程组。为此我...     

烧结金属纤维板大空间自然对流实验研究

实验研究了烧结金属纤维板在大空间下的自然对流换热,分析了倾角、孔隙率、纤维丝经、Ra数和金属纤维导热系数对换热性能的影响.实验结果表明:存在最优的角度(60°左右)使烧结金属纤维板的自然对流换热性能最好,但倾斜角度对烧结金属纤维板的换热影响没有光板显著;加热面的平均Nu数随着纤维直径和孔隙率的增加均先增加后减小;在实验...     

A 3D numerical simulation of mixed convection of a magnetic nanofluid in the presence of non-uniform magnetic field in a vertical tube using two phase mixture model

In this paper, results of applying a non-uniform magnetic field on a ferrofluid (kerosene and 4 vol% Fe₃O₄ ) flow in a vertical tube have been reported. The hydrodynamics and thermal behavior of the flow are investigated numerically using the two phase mixture model and the control volume technique. Two positive and negative magnetic field gradients have been examined. Based on the obtained results the Nusselt number can be controlled externally using the magnetic field with different intensity and gradients. It is concluded that the magnetic field with negative gradient acts similar to Buoyancy force and augments the Nusselt number, while the magnetic field with positive gradient decreases it. Also with the negative gradient of the magnetic field, pumping power increases and vice versa for the positive gradient case.     

Numerical simulations of thermal convection under the influence of an inclined magnetic field by using solenoidal bases

The effect of an inclined homogeneous magnetic field on thermal convection between rigid plates heated from below under the influence of gravity is numerically simulated in a computational domain with periodic horizontal extent. The numerical technique is based on solenoidal (divergence‐free) basis functions satisfying the boundary conditions for both the velocity and the induced magnetic field. Thus, the divergence‐free conditions for both velocity and magnetic field are satisfied exactly. The expansion bases for the thermal field are also constructed to satisfy the boundary conditions. The governing partial differential equations are reduced to a system of ordinary differential equations under Galerkin projection and subsequently integrated in time numerically. The projection is performed by using a dual solenoidal bases set such that the pressure term is eliminated in the process. The quasi‐steady relationship between the velocity and the induced magnetic field corresponding to the liquid metals or melts is used to generate the solenoidal bases for the magnetic field from those for the velocity field. The technique is validated in the linear case for both oblique and vertical case by reproducing the marginal stability curves for varying Chandrasekhar number. Some numerical simulations are performed for either case in the nonlinear regime for Prandtl numbers Pr = 0.05 and Pr = 0.1. Copyright © 2014 John Wiley & Sons, Ltd.     

对流占优的Sobolev方程的投影稳定化有限元方法

对于对流占优的Sobolev方程,提出了一种新的投影稳定化有限元方法,建立了半离散和全离散的投影稳定化格式,给出了解的稳定性和收敛性分析.该方法能够有效克服对流占优,与内罚方法相比,投影格式更简单,计算量更小,且得到的C—N格式是无条件稳定的,时间精度达到了二阶.最后,通过实验证明,数值结果与理论结果完全一致.