共查询到19条相似文献,搜索用时 906 毫秒
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本文在VOSET界面捕捉方法的基础上对控制方程进行修正,使其能够计算带相变的两相流问题,然后用这种方法计算水平壁面上的膜态沸腾。模拟得到的平均Nu数与Klimenko的关联式的计算结果基本一致。计算结果表明,在较低的壁面过热度下,膜态沸腾呈现气泡状流动;在较高的壁面过热度下,膜态沸腾呈现气带状流动。 相似文献
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采用耦合电场模型的相变格子Boltzmann模型,数值研究了电场作用下锥翅结构表面的饱和池沸腾换热.为了定量分析电场对锥翅结构表面沸腾换热影响的机理,首先在无电场作用下对比调查了平滑表面和锥翅表面的沸腾换热现象.发现锥翅结构在核态沸腾阶段有更多的成核点,沸腾换热性能增强,临界热流密度(critical heat flux,CHF)提高.而在过渡沸腾阶段以及膜态沸腾阶段,由于锥翅结构增加了锥翅表面流体的流动阻力,阻碍了气液交换,换热性能低于平滑表面.基于以上发现,通过对锥翅表面池沸腾过程施加电场,进一步强化了锥翅表面沸腾换热.结果表明,在起始核态沸腾阶段,电场的存在稍微延后了气泡开始成核时间,气泡尺寸减小,沸腾轻微被抑制;充分核态沸腾阶段,由于电场力的作用以及电场与锥翅结构协同表现出的尖端效应,阻止了加热表面干斑的扩散和蔓延,促进沸腾换热;过渡沸腾以及膜态沸腾阶段,尖端效应更加明显,逐渐增大的电场强度使沸腾在更高过热度下处于核态沸腾状态,沸腾换热性能大幅度提高,且CHF逐渐提高. 相似文献
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用Gong-Cheng格子Boltzmann方法汽液相变模型数值研究了具有单个和多个微孔的粗糙表面上的池沸腾传热,通过数值模拟得到了含有多个微孔的粗糙加热面上从自然对流区直至膜态沸腾区的池沸腾曲线。模拟结果表明亲水微孔和疏水微孔中存在不同的汽泡成核和生长形态。存在一个临界微孔深度,使得汽泡脱离频率在该处跃升,从而提高沸腾传热量。在粗糙表面上,汽-液-固三相接触线处具有最低的局部温度和最高的局部热流密度。 相似文献
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本文对气流床煤气化炉内高温合成气和壁面渣层的流动与传热传质过程进行了分析,建立了渣层流动、传热传质和相变数理模型,采用VOF方法对渣层和气体之间自由界面进行追踪,采用射线追踪方法(DTRM)计算辐射换热,采用焓法计算渣层相变,熔融态渣滴在渣层表面的沉积通过源项引入.应用所建立的数学模型对实验室规模的Texaco煤气化炉进行了模拟.结果表明:气化炉壁面换热系数从上到下先增加再减少最后再增加;炉膛温度升高,固态渣层厚度减少;壁面温度升高,固态渣层厚度减少. 相似文献
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《工程热物理学报》2010,(6)
通过分析浮法玻璃生产工艺,建立了玻璃液流动的数学模型,引入连续表面力模型(CSF)计算玻璃液运动界面上的表面张力,并使用连续变化处理模型(CTT)对界面物性间断进行连续性处理,提高了数值计算的鲁棒性。在此基础上,采用分段线性方法(PLIC)重构玻璃液、锡液、保护气体之间的自由界面,追踪玻璃液的运动。对不同唇砖坡度的皮尔金顿锡槽入口端进行了模拟,结果表明:PLIC方法能获得具有较高精细性的自由界面,玻璃液进入锡槽后,存在部分玻璃液向后流动的情况,形成滞流,这部分玻璃液由于在高温区停留时间较长,容易造成玻璃质量缺陷,为了避免玻璃液与耐火砖接触,需提供足够滞流区。 相似文献
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本文使用分子动力学方法对金属钨的熔化过程进行了数值模拟,分析了钨在熔化过程中的结构、系统内能变化以及表面熔化过程固-液界面变化情况,初步分析了表面熔化现象的机理。模拟过程采用嵌入原子模型(EAM)描述原子间相互作用,模拟结果表明,嵌入原子模型适合于计算固-液相变过程,表面熔化过程是由表面处最外层原子的不稳定性触发的。对于均匀熔化过程,晶体在4700 K下发生固-液相变;对于表面熔化过程,计算获得了不同温度(3800~4800 K)下的熔化速度,拟合出熔化速度公式,得到的表面熔化热力学熔点与已有实验结果基本符合。 相似文献
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格子Boltzmann方法具有微介观的特性,能够自动捕捉和追踪界面,在多相流领域有广阔的应用前景。对于伴有气液相变的传热问题,格子Boltzmann方法已有模型较少,其中有一部分是通过质量变化间接反映相变过程,不能真实反映温度场的演化和影响。本文采用了模拟多相流动和分离的自由能模型,结合基于Stefan边界的相变传热模型,考虑壁面自由能对流体与壁面间润湿性的影响,模拟了静态接触角、过热壁面的气泡生长和脱离,并进行了更接近真实沸腾过程的随机生成气泡的模拟,以及流动沸腾的气泡生长和脱离的模拟。 相似文献
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《Revue Generale de Thermique》1998,37(2):83-88
This paper describes the influence of an electric field on the heat transfer rate during film boiling of stagnant fluids (pool boiling) on a horizontal surface. Modelling the influence of an electric field on the heat transfer during film boiling requires the knowledge of the equilibrium shape of the liquid-vapour interface. This equilibrium shape is calculated using an iterative solution technique. In each iteration step a fourth order Runge-Kutta technique is used to calculate the shape of the interface and a boundary element method is used to calculate the electric field. It is shown that the vapour bubbles formed on this interface become elongated in the presence of an electric field. This effect is accounted for in the existing heat transfer models in order to describe the influence of the electric field on the heat transfer coefficient during film boiling. 相似文献
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This paper presents a numerical method directed towards the simulation of flows with mass transfer due to changes of phase. We use a volume of fluid (VOF) based interface tracking method in conjunction with a mass transfer model and a model for surface tension. The bulk fluids are viscous, conducting, and incompressible. A one-dimensional test problem is developed with the feature that a thin thermal layer propagates with the moving phase interface. This test problem isolates the ability of a method to accurately calculate the thermal layers responsible for driving the mass transfer in boiling flows. The numerical method is tested on this problem and then is used in simulations of horizontal film boiling. 相似文献
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Modeling Three-Dimensional Multiphase Flow Using a Level Contour Reconstruction Method for Front Tracking without Connectivity 总被引:3,自引:0,他引:3
Three-dimensional multiphase flow and flow with phase change are simulated using a simplified method of tracking and reconstructing the phase interface. The new level contour reconstruction technique presented here enables front tracking methods to naturally, automatically, and robustly model the merging and breakup of interfaces in three-dimensional flows. The method is designed so that the phase surface is treated as a collection of physically linked but not logically connected surface elements. Eliminating the need to bookkeep logical connections between neighboring surface elements greatly simplifies the Lagrangian tracking of interfaces, particularly for 3D flows exhibiting topology change. The motivation for this new method is the modeling of complex three-dimensional boiling flows where repeated merging and breakup are inherent features of the interface dynamics. Results of 3D film boiling simulations with multiple interacting bubbles are presented. The capabilities of the new interface reconstruction method are also tested in a variety of two-phase flows without phase change. Three-dimensional simulations of bubble merging and droplet collision, coalescence, and breakup demonstrate the new method's ability to easily handle topology change by film rupture or filamentary breakup. Validation tests are conducted for drop oscillation and bubble rise. The susceptibility of the numerical method to parasitic currents is also thoroughly assessed. 相似文献
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A second-order hybrid level set-volume constraint method (HLSVC) for numerically simulating deforming boundaries is presented. We combine the HLSVC interface advection algorithm with a two phase flow solver in order to numerically capture deforming bubbles and drops whose actual volume (s) fluctuate about fixed “target” volume (s). Three novel developments are described: (1) a new method for enforcing a volume constraint in which the number of bubbles and drops can change due to merging or splitting, (2) a new, second order, semi-lagrangian narrow band level set reinitialization algorithm, and (3) validation of a two-phase flow numerical method by comparison with linear stability analysis results for a co-flowing liquid jet in gas. The new interface capturing method is tested on benchmark problems in which the velocity is prescribed (passive advection of interfaces) and in which the velocity is determined by the incompressible Navier–Stokes equations for two-phase flow. The error in interface position when using the hybrid level set-volume constraint method is reported for many benchmark problems in polar coordinates, cylindrical coordinates, and on an adaptive grid in which one criteria of adaptivity is the magnitude of the interface curvature. 相似文献
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介绍了过冷沸腾换热的数值模拟方法以及在EAST第一壁组件冷却系统中的应用.采用双流体模型,系统分析了过冷沸腾壁面换热过程中存在的各种换热模式,给出了Fluent软件封闭关系式中所需的质量、动量以及能量的交换项的形式.采用用户自定义函数(UDF)模拟壁面沸腾气化过程,对提出的模拟方法与已发表的实验数据对比进行了校核,得出合理的结论.最后分析了过冷沸腾两相流在EAST第一壁中的工程应用,模拟了热沉冷却结构的沸腾换热现象.为EAST PFCs的冷却结构优化提供了依据. 相似文献
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TeSeIn是一种可逆光存贮介质.分别用单源热蒸发和磁控溅射制备TeSeIn膜.利用透射电镜(TEM)研究了膜的结构和微观形貌.利用俄歇剖面技术(AES-PRO)给出了膜的组分深度剖面,分析了TeSeIn记录介质膜与ZnS保护膜界面间的互扩散大小.利用X光电子能谱(XPS)分析了组元深能级结合能的化学位移.最后根据上面实验结果简要讨论了制备稳定的多元记录介质膜的方法. 相似文献
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Experimental results concerning pool film boiling on a wire under the action of an externally imposed electric field are reported. The working fluid was saturated R113 at atmospheric pressure, the heaters were platinum wires of 0.2, 0.3, and 0.6 mm diameter. An electrostatic field of cylindrical geometry was created around the wire by means of a 60-mm-diameter cylindrical cage in order to assess electrohydrodynamic (EHD) effects on boiling. Voltages up to 15 kV d.c. were applied. The results showed that two different film boiling regimes, separated by an additional boiling crisis, can exist in the presence of an electric field. The first regime, at low wire superheat, is strongly influenced by the electric field, showing a remarkable heat transfer enhancement with increasing voltage. The second one, at higher superheat, is weakly dependent on the field strength and almost coincident with the zero field one. The two film boiling regimes are separated by a transition characterized by a hysteresis cycle, similar to the one between nucleate boiling and first film boiling regime. 相似文献
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