化学气相沉积制备碳纳米管的数值模拟

发布时间：2018-04-05 05:44

本文选题：碳纳米管　切入点：计算流体动力学　出处：《南昌航空大学》2015年硕士论文

【摘要】：碳纳米管因其具备的独特电子、气体吸附以及机械性能,因此被应用到许多领域。目前,大规模生产碳纳米管主要采用化学气相沉积法(CVD法)。然而气相沉积过程复杂,对沉积速率影响的因素较多,利用传统实验方法优化价格昂贵且费时。通过计算机对CVD法制备碳纳米管过程进行模拟,既可以缩短优化工艺参数的周期、而且还能降低成本,并且对沉积过程有更深层次的了解,用实验研究沉积过程有很大的帮助。本文通过耦合流体流动、传热传质、化学反应等物理模型,建立了化学气相沉积法制备碳纳米管过程的二维模型。采用计算流体力学(CFD)方法对生产碳纳米管初期碳源的获取过程进行分析。探讨了不同反应条件下对碳沉积率的影响以及喷嘴式CVD反应器内部结构组成对反应过程的影响。研究内容及结果主要如下:(1)针对CVD反应器内部进口气体速率的改变对反应过程中碳沉积率影响进行分析,结果表明:随着进口速率的增大,各个阶段的碳沉积率增长速率各不相同,速度范围在0.5m/s-5.0m/s上的碳沉积率增长速率是最高的,而当速度大于5.0m/s,碳沉积率增长速率则趋于平缓;(2)针对CVD反应器内部反应温度的改变对反应过程中碳沉积率影响进行分析,结果表明:根据不同温度下碳沉积率变化规律并结合碳纳米管在不同温度下的转化率,推断出最佳反应温度是由该温度下碳沉积量与该温度下碳纳米管转化率两者的乘积所决定的;(3)针对CVD反应器内部气源供给量以及进口气体温度的改变对反应过程中碳沉积率影响进行分析,结果表明:随着气源供给量以及进气温度的增大,碳沉积率均随之而升高,并发现各个阶段的碳沉积率增长速率近似相同,通过曲线拟合获得了气源供给量—碳沉积率以及进口气体温度—碳沉积率两者之间的函数关系式。(4)针对喷嘴式CVD反应器结构的内部组成对碳沉积率的影响进行分析,将内部结构拆分为四种结构,观察各结构之间的有无对反应过程的影响。结果表明:当反应结构没有喷嘴时,增加芯片与否,对于物种分布的影响不大;当反应结构有喷嘴时,芯片对物种质量分布会产生一定的影响,无芯片将会降低碳沉积效率;通过比较四种不同结构反应器的碳沉积速率分布曲线图得知,在相同的外界条件下,比较四种结构的沉积率曲线图,证实了喷嘴式CVD反应器内部结构的组成有利于促进碳沉积率的增加。并且探讨了芯片的高度对碳沉积率变化的影响,发现当芯片高度与进口直径比值小于1/2时,碳沉积率随着芯片高度的增大呈现出明显的递增趋势;而当芯片高度与进口直径比值大于1/2时,碳沉积率随着芯片高度的增大递增趋势不明显。
[Abstract]:Carbon nanotubes (CNTs) have been applied in many fields because of their unique electronic, gas adsorption and mechanical properties.At present, carbon nanotubes are produced by chemical vapor deposition (CVD).However, the process of Vapor deposition is complicated and the factors affecting the deposition rate are many. It is expensive and time-consuming to optimize by traditional experimental methods.The process of preparing carbon nanotubes by CVD method is simulated by computer, which can not only shorten the period of optimizing process parameters, but also reduce the cost, and has a deeper understanding of the deposition process. It is helpful to study the deposition process by experiment.Based on coupled fluid flow, heat and mass transfer, chemical reaction and other physical models, a two-dimensional model for the preparation of carbon nanotubes by chemical vapor deposition has been established in this paper.Computational fluid dynamics (CFD) method was used to analyze the acquisition process of carbon source in the initial production of carbon nanotubes.The influence of different reaction conditions on the carbon deposition rate and the influence of the internal structure of the nozzle type CVD reactor on the reaction process were discussed.The main contents and results are as follows: (1) the influence of the inlet gas rate on the carbon deposition rate in the CVD reactor is analyzed. The results show that: with the increase of the inlet rate,The growth rate of carbon deposition rate varies from stage to stage, and the growth rate of carbon deposition rate in the range of 0.5m/s-5.0m/s is the highest.When the velocity is greater than 5.0 m / s, the increasing rate of carbon deposition rate tends to be flat.) the effect of reaction temperature on carbon deposition rate in CVD reactor is analyzed.The results show that according to the change of carbon deposition rate at different temperatures and the conversion of carbon nanotubes at different temperatures,It is inferred that the optimum reaction temperature is determined by the product of carbon deposition amount and carbon nanotube conversion at that temperature.The effect of carbon deposition rate was analyzed,The results show that the carbon deposition rate increases with the increase of gas supply and inlet air temperature, and it is found that the growth rate of carbon deposition rate is approximately the same at each stage.By curve fitting, the functional relationship between the feed ratio of gas source and the ratio of carbon deposition and the temperature of inlet gas and the rate of carbon deposition are obtained. The influence of the internal composition of nozzle type CVD reactor on the carbon deposition rate is analyzed.The internal structure was divided into four structures and the effect of each structure on the reaction process was observed.The results show that when there is no nozzle in the reaction structure, the increase of the chip has little effect on the species distribution, and when there is a nozzle in the reaction structure, the chip will have a certain effect on the species quality distribution, and the carbon deposition efficiency will be reduced without the chip.By comparing the carbon deposition rate distribution curves of four kinds of reactors with different structures, it is found that under the same external conditions, the deposition rate curves of the four structures are compared.It is proved that the composition of the internal structure of the nozzle CVD reactor is beneficial to the increase of carbon deposition rate.The influence of chip height on carbon deposition rate is discussed. It is found that when the ratio of chip height to inlet diameter is less than 1 / 2, the carbon deposition rate increases obviously with the increase of chip height.However, when the ratio of chip height to inlet diameter is greater than 1 / 2, the increasing trend of carbon deposition rate is not obvious with the increase of chip height.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11;TB383.1

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