In this thesis, three-dimensional lattice Boltzmann multi-phase fluid model is applied to simulate binary fluid systems with large density ratio (1000) and partial wetting surface. It is based on the model of Zheng et...
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In this thesis, three-dimensional lattice Boltzmann multi-phase fluid model is applied to simulate binary fluid systems with large density ratio (1000) and partial wetting surface. It is based on the model of Zheng et al. [26] combined with partial wetting boundary condition of Briant et al. [12]. In the present work, a liquid droplet on a partial wetting surface with given contact angle is simulated for checking the reliability of model. The simulated results are in good agreement with theoretical solutions. In addition, two types of micro-structured surfaces which enhance surface hydrophobicity are also considered in the study. By applying appropriate implementation on micro-structures, the obtained apparent contact angles are also verified by experimental measurement and theoretical prediction with good agreement. Also, the parallel performance is discussed. The parallel efficiency can reach 80% when using 256 cores with a 2D domain decomposition.
润湿性是固体表面的重要性质之一,固体表面的润湿性可以通过改变表面化学性质或者表面形貌来控制。不同表面润湿特性的材料在日常生活、工业生产中有着广泛的应用。探索不同微结构表面形貌对润湿性的影响规律,进而实现通过改变表面形貌控制表面润湿性的研究,具有重要的学术意义和工程应用价值。本文运用等离子体浸没离子注入(Plasma Immersion Ion Implantation,简称PIII)技术在抛光的单晶硅表面制备了山峰状微结构表面形貌,系统研究了 PIII制备工艺中不同刻蚀气体和钝化气体混合比对硅表面形貌和润湿特性的影响,借助扫描电子显微镜(Scanning Electron Microscope,简称SEM)和原子力显微镜(Atomic ForceMicroscope,简称AFM)对表面形貌进行了表征,测量了微结构表面的静态和动态宏观接触角。依据实验获得的表面微结构的形貌表征,建立了参数化微结构表面几何模型,采用VOF方法数值模拟研究了不同类型微结构表面上液滴的铺展过程以及表面微结构参数对润湿性的影响规律。实验研究结果表明:PIII工艺能够在抛光的单晶硅表面制备出明显的“山峰状”微结构,随着气体混合比的增加,凸起结构的高度先增加后轻微减小,而凹凸投影面积比则持续增加。接触角测量结果显示样品表面的宏观接触角受表面化学性质和表面形貌两个因素共同影响,表面粗糙度和面积比的增大都会促进宏观静态接触角的增大。随着PIII工艺中气体混合比增加,动态的前进接触角和后退接触角逐渐增大,接触角滞后随气体流量比的变化则无明显规律。数值模拟研究表明:VOF模型可以较好地实现复杂结构表面上宏观接触角特性的数值模拟;表面微结构的存在阻碍了液滴在表面的铺展,从而改变了液滴在微结构表面上的宏观浸润特性;对于“山峰状”表面微结构三维形貌,采用等效的三角形波形建立的二维轴对称CFD模型,可以准确地预测微结构表面的接触角特性,并与实验结果高度吻合;在体积力作用下光滑表面和复杂微结构表面上液滴的运动过程都包含变形和运动两个过程,光滑表面上液滴呈现整体运动,保持固定的前进角和后退角;在微结构表面上液滴仅部分能发生滑动,液滴保持固定的前进角,而后退角随着液滴滑动铺展逐渐接近于零。
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