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微纳尺度下溶解流动的物理力学研究
Alternative TitleA physical mechanics study of dissolutive flow at micro-/nano-scale
苗青
Thesis Advisor袁泉子
2021-05-23
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline固体力学
Keyword溶解流动、动边界、受限流体、结构演化、标度律
Abstract

溶解流动在自然环境和工业生产中广泛存在,其研究对于解决能源开发、地貌演化、生物医药以及微纳制造等领域中的瓶颈问题发挥着重要作用,同时为解决三相接触线处的关键力学难题 Huh-Scriven 佯谬提供新的思路。与复杂的宏观应用相关联的是溶解流动在微观层面上的关键机制和起源,从微纳尺度出发研究溶解流动的物理本质至关重要。但是由于溶解流动考虑了固体溶解对于体系特征的影响,之前惰性表面的流体力学与受限流体研究框架已经不能完全解释溶解流动动态行为,极大地增加了问题的研究难度。

本文针对溶解流动中的三个关键科学问题:动边界问题、流体物化性质的演化、输运特性的变化。采用物理力学方法,通过机器学习将密度泛函理论、分子动力学模拟和实验观测等多尺度研究方法耦合,从微观出发揭示了溶解流动的物理机理。定量地研究了流体内部的对流和扩散、固体表面溶解、界面演化、尺寸效应与分子间相互作用等因素对于溶解流动的影响。厘清了溶解流动中的标度律、流体流动模式以及固体结构演化,自下而上地分析了溶解流动过程。为实现溶解度流动的预测、控制和优化奠定了理论基础。

液滴在固体表面溶解流动的标度律:选取了高透明度的材料进行实验,结合粒子图像测速技术 (Particle Image Velocity, PIV) 和显微观察,从实验上得到了液体溶解流动的动态过程。开展了大规模的分子动力学模拟,揭示了接触线运动与溶解耦合条件下溶解流动的标度律,阐明了液滴溶解流动不同阶段驱动力的变化。在溶解流动前期,标度律与惰性表面的 Tanner一致,但后期溶解对标度律的影响不可忽略。针对物质溶解造成的表面张力梯度与浓度梯度改变了液体内部流场的问题,我们从理论上重现了液体内部有无对流对液滴铺展标度关系的影响。将微观参数传递到连续介质尺度,结合相场模拟,探索了多尺度下的溶解流动规律。

纳尺度通道内的溶解流动模式:通过调控固体的溶解性,首次实现了纳尺度通道内流动模式从类塞状 (plug-like) 流到类泊肃叶 (Poiseuille-like) 流的转变。不同于纳尺度惰性通道内受限流动呈现出的类塞状流模式,在溶解影响下,尺寸效应与溶解之间的竞争改变了近壁面处的流动特性,边界处产生了新的能量耗散形式。对于受限液体密度而言,惰性表面间受限液体的分层振荡分布被破坏,溶解使流体密度趋向于均匀分布,通过计算得到了密度转变的临界状态。通过总结溶解速度、来流速度与扩散系数之间的标度关系,厘清了通道内的溶解流动模式。

溶解流动中的固体结构演化:通过改变流体流动速度,实现了可溶固体最终结构的优化。引入了一个新的无量纲数,阐明了溶解和对流主导下固体收敛的圆形及近似三角形结构,通过计算得到了固体收敛构形发生变化的临界参数。揭示了可溶固体在流体中的自相似结构演化规律。结合统计平均的流场和溶解速度分布,厘清了溶解结构对初始状态不敏感的原因。探索了流场和浓度场耦合变化条件下,固体面积随时间变化的标度律,定量化地描述了溶解过程,得到了优化的固体结构。

Other Abstract

Fluid flow induced solid evolution widely exists in the environmental applications and industrial processes, its research not only plays an important role in solving the bottleneck problems in the fields of energy, geomorphology, biomedicine and micro-/nano-manufacturing, but also provides a new method for solving the key mechanical problem Huh-Scriven paradox at three-phase contact lines. Hinged to these complicated macroscopic observations on dissolutive flow are key underlying mechanisms and origins on the microscopic level. Thus, it is important to study the physical mechanisms of dissolutive flow from the micro-/nano-scale. However, compared to the fluid flow on the inert solid surface, the dissolutive flow takes into account the effect of solid dissolution on the system characteristics, this means previous conclusions of hydrodynamics and confined fluids cannot fully explain the dynamic behavior of dissolutive flow, which makes it a complicated problem to study.

Focusing on three key scientific problems: moving solid boundary, evolution of physicochemical properties of fluid, changes of transfer properties. By using physical mechanics, multi-scale research method including density functional theory (DFT), molecular dynamics (MD) simulations and experiments was combined through artificial intelligence, and the physical mechanisms of dissolutive flow was revealed. The influences of convection and diffusion inside fluid, solid surface dissolution, interface evolution, size effect and molecular interaction on the dissolutive flow have been explored quantitatively. The scaling law, fluid flow patterns and solid evolution in dissolutive flows have been clarified. A systematic, in-depth and bottom to up study has been carried out to reveal the process of dissolutive flow and provide theoretical guidance for the forecast, control and optimization of dissolutive flow.

Scaling laws of droplet spreading on the soluble solid surface: materials with high transparency have been selected for the experiments, the dynamic process of droplet dissolutive flow has been obtained by combining Particle Image Velocity and microscopic observation. Large-scale MD simulations have also been carried out, the scaling laws of dissolutive flow under the coupling of moving contact line and dissolution is revealed, and the change of driving force in different stages of droplet dissolutive flow is clarified. In the early stage of dissolutive flow, the scaling law satisfies the Tanner law, whereas the influence of dissolution should not be neglected after a period of solid dissolution. For the internal flow field caused by the surface tension gradient and concentration gradient due to solid dissolution, we theoretically reproduce the effects of convection in the liquid on the scaling laws. The microcosmic parameters were transferred to continuum scale, and combined with phase field simulation, the multi-scale dynamics of dissolution flow was explored.

The dissolutive flow patterns in nanochannels: By regulating the solubility of solids, the flow patterns in nanochannels have been firstly transformed from plug-like flow to Poiseuille-like flow. Different from the plug-like mode in inert nanochannels, during dissolutive flow, the competition between size effect and dissolution changes the characteristics of fluid molecules near the walls, and new energy dissipation forms are generated at the boundary. For the confined liquid density, the stratified oscillation distribution of the density of confined liquid between inert surfaces is destroyed, and solid dissolution makes the fluid density distribution tend to be uniform, the critical state of density transition is obtained. By summarizing the scaling relation among the dissolving rate, convection velocity, and diffusion coefficient, the dissolutive flow pattern in channels has been clarified.

The evolution of solid structure in dissolutive flow: The final configuration of the soluble solid is optimized by changing the fluid velocity. A new dimensionless number is introduced to illuminate the circular and quasi-triangular convergent structures of solid, the critical parameter that control the change of solid configuration is calculated. The self-similar evolution structure of soluble solid has been revealed. And by the statistical mean flow field and the quantitative distribution of dissolution velocity, the reason why the solution configuration is insensitive to the initial state is clarified. The scaling law of the solid area with time under the coupling of flow and concentration field is explored. The process of dissolutive flow is quantitatively described, and the optimized solid configuration is obtained.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/86557
Collection非线性力学国家重点实验室
Recommended Citation
GB/T 7714
苗青. 微纳尺度下溶解流动的物理力学研究[D]. 北京. 中国科学院大学,2021.
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