磁重力补偿下泡沫演化动力学基础研究
发布时间：2019-07-08 20:22
【摘要】：随着材料科学的快速发展和广泛应用,对于新型功能材料的研发需求越来越迫切。其中,多孔泡沫材料,作为一种“环保、轻质、高性能”的功能材料,在国内外受到了大量的关注。在泡沫材料的制备过程中,由最初液态泡沫形成到各种泡沫产品的成型及应用,贯穿始末的泡沫演化动力学都起着至关重要的作用。如何合理地控制泡沫演化动力学过程,以获得气泡分布均匀、性能稳定的泡沫材料,是一大研究难题。同时,在理论分析层面,对泡沫演化动力学机制的研究也可对拓扑学中的空间填充理论进行指导,并有助于解决其他物理体系中的结构演化问题。而在泡沫演化动力学过程中,由重力所引起的多尺度(空间、时间)现象一直是科学界所关注的热点和难点。如何消除重力,并长时间、低成本开展低微重力环境下的泡沫演化实验是另一研究难题。基于这一研究现状,本文以液态水泡沫和磁流体泡沫为研究对象,并针对其动力学过程中的泡沫性能、粗化机理、结构演化规律等几项关键科学问题进行实验研究分析。随后,采用本文所设计的“磁重力补偿”这一全新研究手段,以实现模拟的低微重力环境,从而进一步分析磁流体泡沫的演化动力学过程。本文的第一部分,设计了一种全新的磁重力补偿实施方法,该方法是结合磁性流体及亥姆霍兹-麦克斯韦双对线圈而实现的。本文通过数值模拟和实验测量方法分别对双对线圈内的磁场分布及磁流体的有效重力水平进行研究分析。首先,通过有限元模拟软件数值计算和精密特斯拉计对磁场大小及分布进行测量发现,双对线圈中心磁场分布呈线性分布特征,其分布较为均匀,且实验测量结果与数值模拟较为吻合。而后,由磁流体的有效重力水平计算结果可知,在双对线圈中心直径60mm、高60mm的圆柱形区域内实现了90%以上的均匀磁重力补偿,且通过调节麦克斯韦线圈内电流,可以达到磁力完全抵消重力,实现后续实验所需的低微重力条件。本文的第二部分,设计了一套泡沫制备及性能测试装置,并分别以活性剂浓度及重力水平为变量,定量分析水泡沫和磁流体泡沫的起泡性和稳定性。在一定浓度范围内,表面活性剂的添加可以增强水泡沫和磁流体泡沫的性能,其起泡性及稳定性均得到提升,当活性剂浓度增加到一定程度时,泡沫起泡性及稳定性均达到饱和;继续添加表面活性剂,则会造成液膜内活性剂过于富集,泡沫“脆性”增加,稳定性反而降低。同时,通过磁重力补偿下的磁流体泡沫性能实验发现:磁流体泡沫的液相分数增加,这是由于重力被补偿后,析液被抑制,泡沫发生吸液(Foam Imbibition)过程所引起的。而随着有效重力水平的降低,磁流体泡沫的稳定性得以显著提升,这是由于磁重力补偿下,液膜内液相增多,其演化衰减得以抑制。这一结论与国际空间站内的泡沫实验研究基本符合。本文的第三部分,通过实验记录了二维水泡沫及磁流体泡沫的粗化动力学过程,并分析泡沫粗化中的拓扑学演化机制及气泡面积定量演化规律。第一方面,泡沫粗化中可以观察到T1和T2两种拓扑学演化机制:T1过程为相邻边的交换重排,使原本隔开的气泡相连,此过程不会引起气泡个数及其边数的改变;T2过程为体积相对较小的三、四、五边形气泡在压力梯度下发生收缩,直至完全消失,此过程则会减少气泡的个数及其边数。同时,在T2过程中发现,四边形和五边形气泡并不会直接消失,而是随着气泡变小,首先经历一系列T1过程,待其转变为三边形后,再收缩直至完全消失。第二方面,常重力和磁重力补偿条件下,二维泡沫内的气泡面积随时间变化与其边数呈线性关系,均符合冯诺依曼定律。通过磁重力补偿下的磁流体泡沫粗化实验发现,气泡面积演化速率显著变慢,说明粗化过程受到了抑制。而这种抑制效应正是由于外加磁场改变了泡沫的液膜特性,使泡沫变得更加稳定。本文的第四部分,采用有限元商业软件进行了二维单分散泡沫结构演化的数值模拟研究,从而深入了解蜂窝六边形的形成机制。首先,采用水银和空气两相体系来模拟单分散二维泡沫结构演化,证实了蜂窝六边形可在液膜内流体完全流动的情况下形成,这是表面张力作用下的能量最小化过程。而后,通过分析不同时刻下的二维泡沫结构形态可知,气泡间气体会逐步收缩减少,这是由于液膜交界处的“缝合力”引起的,当气泡完全消失时,蜂窝六边形结构便形成。
[Abstract]:With the rapid development and wide application of material science, the research and development of new functional materials is becoming more and more urgent. The porous foam material, as a functional material of the "Environmental protection, light weight, high performance", has received a great deal of attention both at home and abroad. During the preparation of the foam material, the formation and application of the various foam products from the initial liquid foam play a critical role in the foam evolution dynamics through the beginning and the end. How to control the dynamic process of foam evolution reasonably to obtain the foam material with uniform bubble distribution and stable performance is a difficult problem. At the same time, at the theoretical analysis level, the research on the dynamic mechanism of the foam evolution can also guide the space-filling theory in the physics, and help to solve the structural evolution problem in other physical systems. In the process of foam evolution, the phenomenon of multi-scale (space, time) caused by gravity has been the hot and difficult problem of the scientific community. How to eliminate the gravity, and to carry out the foam evolution experiment under the low-micro-gravity environment for a long time and at low cost is another difficult problem. Based on this research, this paper studies the key scientific problems such as foam performance, coarsening mechanism and structural evolution law in the dynamic process of liquid water foam and magnetic fluid foam. Then, the new research method of the "magnetic gravity compensation" designed in this paper is adopted to realize the simulated low-micro-gravity environment, so as to further analyze the process of the evolution of the magnetic fluid foam. In the first part of this paper, a new method of magnetic gravity compensation is designed, which is realized by combining the magnetic fluid and the Helmholtz-Maxwell pair of coils. In this paper, the distribution of the magnetic field and the effective gravity of the magnetic fluid in the two pairs of coils are studied by means of numerical simulation and experimental measurement. First, the magnetic field size and distribution are measured by the finite element simulation software and the precision tesla. The distribution of the magnetic field in the center of the two pairs of coils is a linear distribution. The distribution of the magnetic field is more uniform, and the experimental results are in good agreement with the numerical simulation. According to the calculation result of the effective gravity level of the magnetic fluid, the uniform magnetic force compensation of more than 90% is realized in the cylindrical region with the center diameter of 60 mm and the height of 60 mm of the double-pair coil, and by adjusting the current in the Maxwell coil, the gravity can be completely canceled by the magnetic force, And the low micro-gravity condition required by the follow-up experiment is realized. In the second part of this paper, a set of foam preparation and performance testing device was designed, and the foaming and stability of the water foam and the magnetic fluid foam were quantitatively analyzed with the concentration of the active agent and the gravity level. the addition of the surfactant can enhance the performance of the water foam and the magnetic fluid foam in a certain concentration range, and the foaming property and the stability are improved; when the concentration of the active agent is increased to a certain degree, the foaming property and the stability of the foam reach saturation; and the surfactant is continuously added, Then the active agent in the liquid film is too rich, the foam "friability" is increased, and the stability is reduced. At the same time, the performance of the magnetic fluid foam under magnetic gravity compensation has found that the liquid phase fraction of the magnetic fluid foam is increased, which is caused by the process of the foam generation, after the gravity is compensated. With the decrease of the effective gravity level, the stability of the magnetic fluid foam is greatly improved, due to the increase of the liquid phase in the liquid film due to the magnetic gravity compensation, and the evolution attenuation of the liquid film is suppressed. This conclusion is basically in line with the research of the foam experiment in the International Space Station. In the third part of this paper, the process of coarsening of the two-dimensional water foam and the magnetic fluid foam was recorded by the experiment, and the evolution mechanism and the quantitative evolution of the bubble area were analyzed. in that first aspect, the two types of evolution mechanism of T1 and T2 can be observe in the foam coarsening: the T1 process is the exchange rearrangement of the adjacent side, so that the originally separated air bubbles are connected, the process does not cause the change of the number of bubbles and the number of edges thereof, and the T2 process is three or four smaller in volume, The pentagonal bubble shrinks under the pressure gradient until completely disappears, and this process reduces the number of bubbles and its number of edges. At the same time, in the course of T2, it is found that the quadrilateral and pentagonal bubbles do not disappear directly, but as the bubbles become smaller, a series of T1 processes are first experienced, to be converted into triplets, and then to completely disappear. In the second aspect, under the conditions of gravity and magnetic gravity compensation, the air bubble area in the two-dimensional foam has a linear relationship with the number of its sides over time, and it is in accordance with the von Neumann's law. The experimental results show that the evolution rate of the bubble area is slow, which indicates that the coarsening process is inhibited. This inhibitory effect is due to the fact that the applied magnetic field changes the liquid film properties of the foam, making the foam more stable. In the fourth part of this paper, the numerical simulation of the evolution of two-dimensional single-dispersed foam structure is carried out by using the finite element commercial software, and the formation mechanism of the honeycomb hexagon is well understood. First, a two-phase system of mercury and air is used to simulate the evolution of a single-dispersed two-dimensional foam structure, and it is proved that the honeycomb hexagon can be formed under the condition of complete flow of the fluid in the liquid film, which is the energy minimization process under the action of surface tension. Then, by analyzing the shape of the two-dimensional foam structure at different times, the gas between the air bubbles will shrink gradually, which is caused by the "suture force" at the boundary of the liquid film, and the honeycomb hexagonal structure is formed when the air bubbles completely disappear.
【学位授予单位】：上海大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.4
本文编号：2511850
[Abstract]:With the rapid development and wide application of material science, the research and development of new functional materials is becoming more and more urgent. The porous foam material, as a functional material of the "Environmental protection, light weight, high performance", has received a great deal of attention both at home and abroad. During the preparation of the foam material, the formation and application of the various foam products from the initial liquid foam play a critical role in the foam evolution dynamics through the beginning and the end. How to control the dynamic process of foam evolution reasonably to obtain the foam material with uniform bubble distribution and stable performance is a difficult problem. At the same time, at the theoretical analysis level, the research on the dynamic mechanism of the foam evolution can also guide the space-filling theory in the physics, and help to solve the structural evolution problem in other physical systems. In the process of foam evolution, the phenomenon of multi-scale (space, time) caused by gravity has been the hot and difficult problem of the scientific community. How to eliminate the gravity, and to carry out the foam evolution experiment under the low-micro-gravity environment for a long time and at low cost is another difficult problem. Based on this research, this paper studies the key scientific problems such as foam performance, coarsening mechanism and structural evolution law in the dynamic process of liquid water foam and magnetic fluid foam. Then, the new research method of the "magnetic gravity compensation" designed in this paper is adopted to realize the simulated low-micro-gravity environment, so as to further analyze the process of the evolution of the magnetic fluid foam. In the first part of this paper, a new method of magnetic gravity compensation is designed, which is realized by combining the magnetic fluid and the Helmholtz-Maxwell pair of coils. In this paper, the distribution of the magnetic field and the effective gravity of the magnetic fluid in the two pairs of coils are studied by means of numerical simulation and experimental measurement. First, the magnetic field size and distribution are measured by the finite element simulation software and the precision tesla. The distribution of the magnetic field in the center of the two pairs of coils is a linear distribution. The distribution of the magnetic field is more uniform, and the experimental results are in good agreement with the numerical simulation. According to the calculation result of the effective gravity level of the magnetic fluid, the uniform magnetic force compensation of more than 90% is realized in the cylindrical region with the center diameter of 60 mm and the height of 60 mm of the double-pair coil, and by adjusting the current in the Maxwell coil, the gravity can be completely canceled by the magnetic force, And the low micro-gravity condition required by the follow-up experiment is realized. In the second part of this paper, a set of foam preparation and performance testing device was designed, and the foaming and stability of the water foam and the magnetic fluid foam were quantitatively analyzed with the concentration of the active agent and the gravity level. the addition of the surfactant can enhance the performance of the water foam and the magnetic fluid foam in a certain concentration range, and the foaming property and the stability are improved; when the concentration of the active agent is increased to a certain degree, the foaming property and the stability of the foam reach saturation; and the surfactant is continuously added, Then the active agent in the liquid film is too rich, the foam "friability" is increased, and the stability is reduced. At the same time, the performance of the magnetic fluid foam under magnetic gravity compensation has found that the liquid phase fraction of the magnetic fluid foam is increased, which is caused by the process of the foam generation, after the gravity is compensated. With the decrease of the effective gravity level, the stability of the magnetic fluid foam is greatly improved, due to the increase of the liquid phase in the liquid film due to the magnetic gravity compensation, and the evolution attenuation of the liquid film is suppressed. This conclusion is basically in line with the research of the foam experiment in the International Space Station. In the third part of this paper, the process of coarsening of the two-dimensional water foam and the magnetic fluid foam was recorded by the experiment, and the evolution mechanism and the quantitative evolution of the bubble area were analyzed. in that first aspect, the two types of evolution mechanism of T1 and T2 can be observe in the foam coarsening: the T1 process is the exchange rearrangement of the adjacent side, so that the originally separated air bubbles are connected, the process does not cause the change of the number of bubbles and the number of edges thereof, and the T2 process is three or four smaller in volume, The pentagonal bubble shrinks under the pressure gradient until completely disappears, and this process reduces the number of bubbles and its number of edges. At the same time, in the course of T2, it is found that the quadrilateral and pentagonal bubbles do not disappear directly, but as the bubbles become smaller, a series of T1 processes are first experienced, to be converted into triplets, and then to completely disappear. In the second aspect, under the conditions of gravity and magnetic gravity compensation, the air bubble area in the two-dimensional foam has a linear relationship with the number of its sides over time, and it is in accordance with the von Neumann's law. The experimental results show that the evolution rate of the bubble area is slow, which indicates that the coarsening process is inhibited. This inhibitory effect is due to the fact that the applied magnetic field changes the liquid film properties of the foam, making the foam more stable. In the fourth part of this paper, the numerical simulation of the evolution of two-dimensional single-dispersed foam structure is carried out by using the finite element commercial software, and the formation mechanism of the honeycomb hexagon is well understood. First, a two-phase system of mercury and air is used to simulate the evolution of a single-dispersed two-dimensional foam structure, and it is proved that the honeycomb hexagon can be formed under the condition of complete flow of the fluid in the liquid film, which is the energy minimization process under the action of surface tension. Then, by analyzing the shape of the two-dimensional foam structure at different times, the gas between the air bubbles will shrink gradually, which is caused by the "suture force" at the boundary of the liquid film, and the honeycomb hexagonal structure is formed when the air bubbles completely disappear.
【学位授予单位】：上海大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.4
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