超声微泡发生方法及装置设计研究

发布时间：2018-10-09 10:26

【摘要】：湿法制备多晶硅太阳电池表面绒面结构，实际上是溶液中离子和多晶硅相互作用的过程，但是离子运动一般不可控，导致其腐蚀得到的微结构始终不理想。“离子泡”有可能改变这一现象。“离子泡”实际上是在湿法腐蚀过程中利用超声产生的微气泡表面带电特性吸附离子，形成“离子+泡”结构，从而可以实现离子的可控。但是对于这一模型研究依赖于对超声产生的微气泡带电特性机理的研究，目前这方面还缺乏定性研究。为此首先要展开对超声微泡装置研究，为日后超声微气泡特性研究打下基础。首先，，对超声气泡产生过程进行了分析，并根据超声在水中产生空穴的所需要的声压条件计算模型出发，分析了相关因素对超声气泡形成过程，以此为基础设计了超声微气泡的发生装置。其次，对超声系统机械部分进行了设计，分别用等效电路法设计和传统解析法确定了超声换能器和变幅杆的机械参数。为保证设计的可靠性，文中对设计的变幅杆进行了有限元模拟。运用模态分析得出其固有谐振频率和设计工作频率之间误差在允许范围之内，运用谐响应分析得出其端面输出位移和最大应力要求也均满足设计要求。然后利用FLUNENT软件建立了超声微泡发生器数学计算模型及赋予相应的初始边界条件，对各种可能影响气泡生成效果的因数进行数值模拟。文中重点模拟了超声功率、气孔孔径、气体种类、变幅杆结构等影响。通过流场的模拟得出，超声功率对气泡的影响最为显著，在无功率以及低功率的条件下，只会产生宏观的气泡；同时气孔孔径影响在于与超声功率协调性；从模拟的结果上看气体种类对微气泡产生的影响不显著；在模拟中更改了发生器的结构，将其由平面型结构改成凹球面结构，模拟结果说明这种结构对流场的压力有显著的加强过程，而这种压力对流场局部作用明显，对于气泡产生过程也有较大的影响。最后，开展了超声气泡发生器实际效果测试实验，测试实验中主要就功率对气泡产生情况进行分析，得出结果和实际模拟结果可以很好的符合。通过利用高速摄影机得到照片结果分析得到，可以产生微米级的气泡。通过论文研究，初步实现了超声微气泡装置的研究，并通过二相流的模拟得出气泡生成过程中影响关键因素。这为后期进一步研制可控大小、可控数目微气泡用于超声微气泡特性研究提供了依据。
[Abstract]:Wet fabrication of surface suede structure of polycrystalline silicon solar cells is actually a process of interaction between ions and polysilicon in solution, but the ion movement is generally uncontrollable, resulting in the microstructure obtained by corrosion is always not ideal. Ion bubbles may change this phenomenon. In fact, "ion bubble" is used to adsorb ions on the surface of micro-bubble produced by ultrasonic in the process of wet corrosion, forming "ion bubble" structure, so that the ion can be controlled. However, the study of this model depends on the study of the mechanism of charge characteristics of microbubbles produced by ultrasound, which is still lack of qualitative research. Therefore, the research of ultrasonic microbubble device should be carried out first, which will lay a foundation for the study of ultrasonic microbubble characteristics in the future. Firstly, the process of ultrasonic bubble formation is analyzed, and based on the model of sound pressure conditions needed to generate holes in water, the relevant factors are analyzed. Based on this, a device for generating ultrasonic microbubbles is designed. Secondly, the mechanical part of ultrasonic system is designed, and the mechanical parameters of ultrasonic transducer and amplitude bar are determined by the method of equivalent circuit and the traditional analytical method. In order to ensure the reliability of the design, finite element simulation of the designed horn is carried out in this paper. The error between the inherent resonance frequency and the design working frequency is found to be within the allowable range by modal analysis, and the output displacement and maximum stress requirements of the end face are also satisfied by the harmonic response analysis. Then the mathematical calculation model of ultrasonic microbubble generator and the corresponding initial boundary conditions are established by using FLUNENT software. The various factors that may affect the effect of bubble formation are simulated numerically. The effects of ultrasonic power, pore aperture, gas type and amplitude-varying bar structure are simulated. Through the simulation of flow field, it is concluded that ultrasonic power has the most significant effect on bubbles, and only macrobubbles can be produced under the condition of no power and low power, meanwhile, the influence of pore aperture is the coordination with ultrasonic power. From the result of simulation, the effect of gas type on microbubble is not significant. In the simulation, the structure of generator has been changed from plane structure to concave spherical structure. The simulation results show that the pressure of the flow field of this kind of structure has a significant strengthening process, and the local effect of this pressure flow field is obvious, which also has a great influence on the bubble production process. Finally, the practical effect test experiment of ultrasonic bubble generator is carried out. In the test experiment, the power of the bubble is analyzed, and the results are in good agreement with the actual simulation results. By using the high speed camera to get the result of the photo, the micrometer bubble can be produced. Through the research of this paper, the research of ultrasonic micro-bubble device is realized, and the key factors of bubble formation are obtained through the simulation of two-phase flow. This provides a basis for the further development of controllable size and number of microbubbles for the study of ultrasonic microbubbles.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM914.4;TB559

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