泡沫铝制备中析液过程的微观－宏观数值研究

通过微元管内流动模型研究液态金属熔体泡沫体内单条Plateau边界内析液过程中的速度场.分析不同牛顿表面粘度,即不同的气液界面运动能力(无量纲参数M)条件下,Plateau边界内速度的分布.结果显示,在相同的气液界面运动能力和曲率半径条件下,泡沫体内固壁处Plateau边界内速度约是内部Plateau边界内速度的6～8倍,从而解释不同容器内泡沫体析液速率的差异现象;发现M存在一个临界值,在此值的两边,液膜厚度与曲率半径的比值对Plateau边界内速度的影响呈现出相反的趋势.进而利用微观计算结果建立了泡沫体的整体宏观析液模型,将模型计算结果和经典析液方程计算结果及实验值作了比较,结果表明,模型计算结果与实验值在泡沫层上部、中部吻合较好,M值和气泡大小对析液过程有显著影响.

Microscopical and Macroscopical Numerical Study on the Drainage Process in the Fabrication of Foamed Aluminum

Velocity field in a single plateau border of aluminum foam during drainage process is studied by a mathematic model for the flow inside a micro-channel. It is shown that the liquid/gas interface mobility, which is characterized by the Newtonian surface viscosity, has substantial effect on the velocity inside single plateau border. It is found that at the same liquid/gas interfacial mobility (M) and same radius of curvature, the max velocity inside an exterior plateau border is about 6~8 times as large as that inside an interior plateau border. A critical value of the interfacial mobility is found in the interior plateau border, and for values greater or less than which the effects of the film thickness on the velocity in plateau border show opposite tendencies. Based on the results from the microscopical model, a new macroscopical drainage model is presented for aluminum foams. Comparisons of computed results by this model with experimental data from the literature and with those from the classical drainage equation show a reasonable agreement. Furthermore, computational results reveal that the liquid holdup of foams is dependent strongly on the value of and bubble radius.